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Android Basics
Mobile Application Development
Selected Topics – CPIT 490
30-Apr-17
Overview
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Review
Android Activities
Android Intents
User Interface / Views
User Notifications
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Developing for Android
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Eclipse
Android SDK
Android Development Tools (ADT)
Android Virtual Devices (AVD) & SDK Manager
The Android Emulator
Dalvik Debug Monitor Services (DDMS)
The Android Debug Bridge (ADB)
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Android Software Stack
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Android Project Structure
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src/ - Java packages. Each package can have multiple .java files representing different
classes.
res/layout/ - XML files that specify the layout of each screen.
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main.xml defines the layout of the application. Default view is Layout view.
res/values/ - XML files used as references by other files.
res/drawable-hdpi/ , res/drawable-mdpi/ , and res/drawable-ldpi/ - high, medium,
and low dots-per-inch resolution pictures.
res/color, res/menu, res/anim
assets/ - additional non-media files. Assets used by application. Ex. HTML, database,
etc
AndroidManifest.xml specifies the project to the Android OS. Permissions and other
features are specified here.
Auto-generated files (do not modify):
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gen/ contains auto-generated code. Class R.java generated by Android Asset
Packaging Tool (aapt). ). If you delete R.java, it will auto-generated again.
R.java is based on AndroidManifest.xml file.
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default.properties contains project settings.
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Android Application Components
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i) Activity: Activity is a visual screen for interaction of user with the
application. Depends upon design, an application may consists of one or
more activities
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Fragments: "miniature" activities that could be grouped to form an activity
ii) Views: The User interface of an Activities is build with widgets.
iii) Service: Service do not have a visual interface, it runs in the back
ground, like play back music and fetching data from the network.
iv) Broadcast Receiver: Broadcast receiver receive broadcast
announcements and response to them according to the situation.
v) Content Provider: Content provider is a SQLite database, which
supports the sharing and accessing of data among applications.
vi) Intents: Asynchronous messages which allow the application to
request functionality from other services or activities.
vii) Others parts are Android widgets / Live Folders and Live Wallpapers.
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Android Activity
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http://developer.android.com/reference/android/app/Activity
An "activity" is an application component that provides a screen with which
users can interact
Activity is usually a single screen
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Implemented as a single class extending Activity
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Displays user interface controls (views)
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Reacts on user input / events
An application typically consists of several activities
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Each screen is typically implemented by one activity
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Each activity can then start another activity (new screen)
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An activity may return a result to the previous activity
"main" activity is presented to the user when launching the application for the
first time.
Each activity receives callbacks due to a change in its state during its lifecycle
— whether the system is creating it, stopping it, resuming it, or destroying it. 7
Activity Lifecycle
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Activity Lifecycle
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Foreground Lifetime is until
onPause()
Visible Lifetime is until
onStop()
Entire Lifetime is until
onDestroy()
Create an activity by
extending Activity base class
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Activity Example
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extends Activity base class
UI from res/layout folder
R.layout.main refers to main.xml
AndroidManifest.xml must
declare all activities in the
application
@string refers to strings.xml in
res/values folder
onCreate() is involved when the
activity is loaded
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Activity Callbacks
public class Activity extends ApplicationContext {
 protected void onCreate(Bundle savedInstanceState);
// Called when the activity is first created. Provides you with a
Bundle containing the activity's previously frozen state, if there was
one. Always followed by onStart().
 protected void onStart();
// Called when the activity is becoming visible to the user. Followed
by onResume() if the activity comes to the foreground, or onStop()
if it becomes hidden.
 protected void onRestart();
// Called after your activity has been stopped, prior to it being
started again. Always followed by onStart()
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Activity Callbacks
protected void onResume();
// Called when the activity will start interacting with the user. At this point your activity is
at the top of the activity stack, with user input going to it. Always followed by onPause().
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protected void onPause();
// Called when the system is about to start resuming a previous activity. Implementations
of this method must be very quick because the next activity will not be resumed until this
method returns. Followed by either onResume() or onStop().
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protected void onStop();
// Called when the activity is no longer visible to the user. Followed by either onRestart() if
this activity is coming back to interact with user, or onDestroy() if this activity is going
away.
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protected void onDestroy();
// The final call you receive before your activity is destroyed. This can happen either
because the activity is finishing or someone called finish() on it, or because the system is
temporarily destroying this instance of the activity to save space. You can distinguish
between these two scenarios with the isFinishing() method.
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}
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Activity Life cycle
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Activity is destroyed when the back button is pressed. So, if you want to
preserve the state, we need to store the information before the application is
destroyed
onPause() is called when the application is send to background or when the
application is killed
onCreate() is invoked when the activity is loaded for the first time
onStart() and onResume() are invoked when an activity is started, either from
background or newly started
Use the onCreate() method to create and instantiate the objects that you will be
using in your application
Use the onResume() method to start any services or code that needs to run
while your activity is in the foreground.
Use the onPause() method to stop any services or code that does not need to
run when your activity is not in the foreground.
Use the onDestroy() method to free up resources before your activity is
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destroyed.
Utilizing Activity Lifecycle Functions
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Simple exercise to see the activity lifecycle in
action
each overridden function is explicit and a Toast
command is added to show on screen when the
function is entered
Run it on an Android device and try various
cases:
Changing the screen orientation destroys and
recreates the activity from scratch.
Pressing the Home button pauses the activity,
but does not destroy it.
Pressing the Application icon might start a
new instance of the activity, even if the old
one was not destroyed.
Letting the screen sleep pauses the activity and
the screen awakening resumes it. (This is similar
to taking an incoming phone call.)
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Activity Lifecycle Samples
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Turn Display
 onCreate(null) -> onStart -> onResume() -> [Turn Display] >
onSaveInstanceState() -> onPause() -> onStop() ->
onDestroy() -> onCreate() -> onStart() ->
onRestoreInstanceState() -> onResume()
Home
 onCreate(null) -> onStart -> onResume() -> [Home Button]
> onSaveInstanceState() -> onPause() -> onStop() -> [Start
App] > onRestart() -> onStart() -> onResume()
Phone Call Interrupt
 onCreate(null) -> onStart -> onResume() -> [Phone Call] >
onSaveInstanceState() -> onPause() -> onStop() -> [Hang Up
or press Back] > onRestart() -> onStart() -> onResume()
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Notes on Activity
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Starting Activity:
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void startActivity (Intent intent)
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void startActivityForResult (Intent intent, int requestCode)
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void onActivityResult (int requestCode, int resultCode, Intent data)
Shutting Down Activity:
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void finish ()
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void finishActivity (int requestCode)
Saving Activity Status
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void onSaveInstanceState (Bundle outState)
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void onRestoreInstanceState (Bundle savedInstanceState)
Activity A starts Activity B:
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A's onPause()
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B's onCreate() , onStart() , and onResume() (Activity B now has user
focus.)
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A’s onStop() , if A is no longer visible
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Starting Activity
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Saving Activity’s State
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Back Stack
Tasks and Activities
Multiple Tasks
Multiple Activity Instances
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Activity and AndroidManifest.xml
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Any new activity must be defined in AndroidManifest.xml file
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AndroidManifest.xml and main.xml
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versionCode: used to indicate the version number of the application
versionNumber: Represented as <major>.<minor> version numbers. This is displayed
to the user
Minimum, target and maximum SDK versions are specified here
Icon of the application is provided via @drawable, which refers to the res/drawable
folder
The name of the main activity is provided. Also, the package name is provided
android.intent.action.MAIN means that the current activity is the first activity that will
be loaded when the application runs
Under intent-filter <action android:name="a.b.c.d" /> means this specific activity
could be invoked using a.b.c.d as the name
android:windowSoftInputMode="stateHidden" is used to disable soft keyboard from
appearing automatically for EditText
main.xml
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android:onClick="onClick" is used to say which method to call when the view is
clicked. The one in the quotes indicate the name of the method. This method is to
be implemented in the java program.
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Notes on Activity Contd…
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Killing an activity does not remove the application from memory, even if the
application has only one activity
Context class is used to provide references to your application. Activity class is
a subclass of Context class.
To draw progress dialogs, you could use progressDialog class.
Applying dialog themes to an activity (in AndroidManifest.xml) (BAAD Pg 41)
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android:theme="@android:style/Theme.Dialog">
Hides a feature (in *.java file) – Hide the title based on a state (BAAD Pg 42)
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import android.view.Window;
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//---hides the title bar--
requestWindowFeature(Window.FEATURE_NO_TITLE);
Dialog box (BAAD Pg 42)
Creating multiple activities and linking them using Intent (BAAD Pg 54)
Passing parameters through intents (BAAD Pg 63)
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Intents
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http://developer.android.com/reference/android/content/Intent.html
Intents are used as a message-passing mechanism within your application and between
applications. Intents are used to call built-in applications like Map, Browser, etc.
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Explicit start Activity/Service using its class name
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Start Activity/Service for an action with specific data
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Broadcast that an event has occurred
Consists of
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Component name (name of component/activity to handle the intent)
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Action to be performed (MAIN / VIEW / EDIT / PICK / DELETE)
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Data to act on (expressed as URI) or Bundle
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Categories
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Extras (primitives / Strings / Serializable)
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Flags
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Component Name Field
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Specifies the name of the component (name of the activity if the component is
activity) that should handle the intent
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Class name of the target component (for example "FirstActivity")
<activity android:name =".FirstActivity" android:labe l="@string/app_name">
<intent-filter >
<action android:name = "edu.odu.examples.IntentActivity" />
<category android:name = "android.intent.category.LAUNCHER" />
</intent-filter >
</activity >
Setting component name is optional
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Explicit Intent: If it is set, the Intent object is delivered to an instance of the
designated class.
Intent intent = new Intent (this, FirstActivity.class);
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Implicit Intent: If it is not set, Android uses other information (i.e., action field)
in the Intent object to locate a suitable target - this is called "intent resolution"
Intent intent = new Intent ("edu.odu.examples.IntentActivity");
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Launching Activity
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Intent Invocation
Launch new activity (without receiving a result)
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Launch new activity and expect result
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requestCode is simply an integer value that identifies an activity you are
calling. This is to used to identify the activity that returns
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For example, you may be calling multiple activities at the same time, and
some activities may not return immediately (for example, waiting for a
reply from a server)
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requestCode of -1 is like startActivity(intent)
When activity exits, onActivityResult() method is called with given
requestCode (int > 0)
onActivityResult(int requestCode, int resultCode, Intent result)
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Intents and Intent Filters
Intent Filters
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Description of what intents an activity can handle
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Activities publish their intent filters in a manifest file
<intent-filter >
<action android:name="android.intent.action.VIEW"/>
<category android:name="android.intent.category.DEFAULT"/>
<category android:name="android.intent.category.BROWSABLE"/>
<data android:scheme="geo"/>
</intent-filter>
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Upon invocation of startActivity(intent) the system looks at the intent filters of
all installed applications
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Candidate activity that owns the filter must pass matching tests for action,
category, and data fields
http://developer.android.com/guide/topics/intents/intents-filters.html
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.MAIN Action & .LAUNCHER Category
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Activities that can initiate applications have filters with
"android.intent.action.MAIN" specified as the action
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This is a way an application gets started fresh, without a reference to any
particular data.
If they are to be represented in the application launcher, they also specify the
"android.intent.category.LAUNCHER" category:
<intent-filter . . . >
<action android:name="code android.intent.action.MAIN" />
<category android:name="code android.intent.category.LAUNCHER" />
</intent-filter>
The Android system populates the application launcher by finding all the
activities with intent filters that specify the "android.intent.action.MAIN"
action and "android.intent.category.LAUNCHER" category. It then displays
the icons and labels of those activities in the launcher.
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Action Field
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In Android, intents usually come in pairs: action and data. The action describes what is
to be performed, such as editing an item, viewing the content of an item, and so on. The
data specifies what is affected, such as a person in the Contacts database. The data is
specified as an Uri object.
Intent Resolution: Android OS looks for the activities which could satisfy the given
request. For ex., when we specify Intent i = new Intent("android.intent.action.VIEW");
the appropriate activity should be used to view.
A string naming the action to be performed
The Intent class defines a number of predefined action constants, including
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ACTION_CALL, ACTION_EDIT, ACTION_MAIN, ACTION_SYNC,
ACTION_BATTERY_LOW, etc.
You can also define your own action strings for activating the components in your
application
The action largely determines how the rest of the intent is structured - particularly the
data and extras fields - much as a method name determines a set of arguments and a
return value.
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Intent Actions
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Note that Actions’ "Constant" could be replaced with an equivalent String
constant.
e.g.,: ACTION_CALL = "android.intent.action.CALL"
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Data Field
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The URI of the data to be acted on and the MIME type of that data. Use Uri.parse to convert
string to an uri object
Different actions are paired with different kinds of data specifications.
If the action field is ACTION_EDIT, the data field would contain the URI of the document to be
displayed for editing.
If the action is ACTION_CALL, the data field would be a tel: URI with the number to call.
If the action is ACTION_VIEW and the data field is an http: URI, the receiving activity would
be called upon to download and display whatever data the URI refers to.
Examples of Action/Data Pairs
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ACTION_VIEW content://contacts/people/ -- Display a list of people to browse through.
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ACTION_VIEW content://contacts/people/1 – Display information about person whose id is
"1".
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ACTION_DIAL content://contacts/people/1 – Display the phone dialer with the person filled
in.
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ACTION_VIEW tel:123 -- Display the phone dialer with the given number filled in.
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ACTION_DIAL tel:123 -- Dial the phone dialer with the given number filled in.
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Example of Actions
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Starting Activity:
void startActivity (Intent intent)
Intent i = new Intent (this, OtherActivity.class);
startActivity(i);
void startActivityForResult (Intent intent, int requestCode)
 void onActivityResult (int requestCode, int resultCode,
Intent data)
Shutting Down Activity:
void finish()
Intent intent = new Intent (this, FirstActivity.class);
startActivity (intent);
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Notes on Activity and Intents
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use the putExtra() method of an Intent object to add a name/value pair
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Two parameters in putExtra(): one of type string and one of type integer
you can also create a Bundle object and then attach it using the putExtras() method
getIntent() method is used to get Intent object
When a fragment is being created, it goes through the following states: onAttach(),
onCreate(), onCreateView(), onActivityCreated()
When the fragment becomes visible, it goes through these states: onStart(), onResume()
When the fragment goes into the background mode, it goes through these states:
onPause(), onStop()
When the fragment is destroyed (when the activity it is currently hosted in is
destroyed), it goes through the following states: onPause(), onStop(), onDestroyView(),
onDestroy(), onDetach()
Like activities, you can restore an instance of a fragment using a Bundle object, in the
following states: onCreate(), onCreateView(), onActivityCreated()
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Notes on Activity and Intents
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onAttached() — Called when the fragment has been associated with the activity
onCreateView() — Called to create the view for the fragment
onActivityCreated() — Called when the activity’s onCreate() method has been returned
onDestroyView() — Called when the fragment’s view is being removed
onDetach() — Called when the fragment is detached from the activity
<category android:name="android.intent.category.DEFAULT" /> should be used if you
want an activity to be invoked by others
Intents can be specified with categories in AndrodManifest.xml file. You could specify
the category in the code using addCategory(). If no category is specified in the java
code, the DEFAULT category is invoked. If the category specified in the java code is
not matched, then a runtime exception is generated and the activity will not be started
Creating multiple activities and linking them using Intent (BAAD Pg 54)
Passing parameters through intents (BAAD Pg 63)
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Notes on Activity and Intents
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Using intents to start a second activity
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Remember to add new Activity(s) to AndroidManifest.xml !
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Intent intent = new Intent(Context packageContext, Class<?> class);
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packageContext = the activity we’re coming from
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Class: the Activity in our app we’re going to
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Intent intent = new Intent(this, AnotherActivity.class);
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startActivity(i);
Requesting and starting another application’s activity
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Intent intent = new Intent(<action>, <data>);
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ACTION_VIEW, ACTION_EDIT, ACTION_DIAL
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scheme://host/data/segments
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Intent intent = new Intent(Intent.ACTION_DIAL,
Uri.parse(“tel:1234567890”));
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Notes on Activity and Intents
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Activity Results
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startActivityForResult(intent) allows us to “return” data to the calling
Activity
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onActivityResult(int requestCode, int resultCode, Intent data);
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requestCode: unique integer to determine what Activity returned
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resultCode: RESULT_OK, RESULT_CANCELED
 data: Intent to receive additional data
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setResult(int resultCode, Intent data);
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resultCode: RESULT_OK, RESULT_CANCELED
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data: Intent to pass additional data
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finish() pops from stack and sends control back to previous Activity
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Notes on Activity and Intents
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Bundle objects store key and value pairs via the put<type>
methods and get<type> methods
 Basic data types: boolean, byte, char, double, float, int, long,
etc.
 Non-primitives: String, Serializable, Arrays
Can get size() and keySet()
intent.putExtras(Bundle bundle);
 Associate a bundle with an intent
getIntent().getExtras();
 Get bundle associated with an intent
intent.putExtra(String key, value);
 intent.getExtra(String key);
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Fragments
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Fragments are mini-activities
Fragments contain views as like Activities
Fragments are contained within an activity. Fragments could be dynamically
added or removed from the activity
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the FragmentManager class is used to add fragments to an activity.
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the FragmentTransaction class is used to perform fragment transactions in
your activity (such as add, remove or replace)
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the WindowManager to determine whether the device is currently in
portrait mode or landscape mode
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android.R.id.content refers to the content view of the activity
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commit() method is to make changes to effect
Add frames at run-time (BAAD Pg 74)
When an activity goes background, it is moved to back state automatically. For
fragments, moving to back state has to be done using addToBackStack().
Call inbuilt applications using Intent (BAAD Pg 85)
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Fragments
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Three subclasses of fragments: ListFragment, DialogFragment, and
PreferenceFragment
A list fragment is a fragment that contains a ListView, displaying a list of items
from a data source such as an array or a Cursor
In the onCreate() event, you use the setListAdapter() method to
programmatically fill the ListView with the content of the array
The ArrayAdapter object manages the array of strings that will be displayed by
the ListView
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User Interfaces and Views
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Views are loaded from res/layout/main.xml file in the onCreate() method
handler in your Activity class, using the setContentView() method of the
Activity class
Sometimes, you need to code the views in the java code itself because you
need to generate the views at runtime. Ex. Games
http://developer.android.com/guide/topics/ui/index.html
Views and View Groups
Views (Widgets)
Layouts
Events
Menus
Dialogs
Styles and themes
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Fundamental UI Design
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Views
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Visual interface element (controls or widgets)
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A view derives from the base class android.view.View
ViewGroup
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Contains multiple widgets. Layouts inherit the ViewGroup class. Ex
LinearLayout, AbsoluteLayout (deprecated), TableLayout, FrameLayout,
etc
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A ViewGroup derives from the base class android.view.ViewGroup
Activities
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Screen being displayed to the user.
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Assign a View or layout to an Activity
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Layouts
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http://developer.android.com/guide/topics/ui/declaring-layout.html
Layout contains Views
FrameLayout
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Each child view is in reference to the top left corner. Use if only one View
in screen at a time.
LinearLayout
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Views in line, either vertically or horizontally. Single column or single
row. Elements appear in order they are specified in the file
RelativeLayout
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Define positions of each other child view relative to each other and screen
boundaries
TableLayout
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Rows and Columns
Web View
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Display web pages
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Layout Examples
Linear Layout Relative Layout
Grid Layout
Tab Layout
dp or dip — Density-independent pixel. 1 dp is equivalent to one pixel on a 160
dpi screen. Recommended for layout dimensions.
sp — Scale-independent pixel. This is similar to dp and is recommended for
specifying font sizes.
pt — Point. A point is defined to be 1/72 of an inch, based on the physical screen
size.
px — Pixel. Corresponds to actual pixels on the screen. Not recommended.
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Android Specifications
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Nexus S has a 4-inch screen (diagonally), with a
screen width of 2.04 inches. Its resolution is 480
(width) 800 (height) pixels. With 480 pixels
spread across a width of 2.04 inches, the result is
a pixel density of about 235 dots per inch (dpi).
The pixel density of a screen varies according to
screen size and resolution.
Android defines and recognizes four screen
densities:
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Low density (ldpi) — 120 dpi
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Medium density (mdpi) — 160 dpi
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High density (hdpi) — 240 dpi
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Extra High density (xhdpi) — 320 dpi
Nexus S is in hdpi as its dpi is close to 240 dpi.
Actual pixels = dp * (dpi / 160), where dpi is
either 120, 160, 240, or 320.
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Defining Layout
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Using the dp unit ensures that your views are always displayed in
the right proportion regardless of the screen density
Portrait mode:
 res/layout/main.xml
Landscape mode:
 res/layout-land/main.xml
The default orientation layout is horizontal
Each Activity can have it's own layout
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Handling Orientation Changes
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Anchoring
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Anchor your views to the corners (edges of the screen)
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Achieved using RelativeLayout using options like
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android:layout_alignParentTop="true"
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android:layout_alignParentRight="true"
Resizing and repositioning
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Resizing every view according to the orientation
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Write two main.xml files. One in res/layout folder and the other in res/layout-land
folder
Changing orientation kills an activity and recreates it. Only views that are named with
android:id will persist orientation changes
When an activity is killed, onPause() and onSaveInstanceState() methods are invoked
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Unlike the onPause() method, the onSaveInstanceState() method is not fired when
an activity is being unloaded from the stack (such as when the user pressed the
back button), because there is no need to restore its state later
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Preserve the state of your activity, such as using a database, internal or external
file storage, and so on
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Handling Orientation Changes
Easier way to save state: onSaveInstanceState() method provides a Bundle
object as an argument so that you can use it to save your activity’s state
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Information can only be saved in Bundle object and thus complex data
structures cannot be stored
@Override
public void onSaveInstanceState(Bundle outState) {
//---save whatever you need to persist--outState.putString(“ID”, “1234567890”);
super.onSaveInstanceState(outState);
}
@ Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
//---retrieve the information persisted earlier--String ID = savedInstanceState.getString(“ID”);
}

46
Handling Orientation Changes
onRetainNonConfigurationInstance() method is fired when an activity is about
to be destroyed due to a configuration change (such as a change in screen
orientation, keyboard availability, etc.)
@Override
public Object onRetainNonConfigurationInstance() {
//---save whatever you want here; it takes in an Object type--return(“Some text to preserve”);
}

To extract the saved data, you can extract it in the onCreate() method, using
the getLastNonConfigurationInstance() method:
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Log.d(“StateInfo”, “onCreate”);
String str = (String) getLastNonConfigurationInstance();
}

47
Detecting Orientation Changes
Use WindowManager class
//---get the current display info--WindowManager wm = getWindowManager();
Display d = wm.getDefaultDisplay();
if (d.getWidth() > d.getHeight()) {
//---landscape mode--Log.d(“Orientation”, “Landscape mode”);
}
else {
//---portrait mode--Log.d(“Orientation”, “Portrait mode”);
}

Also, you could add android:screenOrientation=”landscape” to activity in
AndroidManifest.xml

If you wish to keep your application displayed in certain orientation, specify the below
in onCreate()
//---change to landscape mode--setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
For Portrait: ActivityInfo.SCREEN_ORIENTATION_PORTRAIT
48

Example of Layout


fill_parent fills the entire width or height of the parent
wrap_content make the width or height to the content
49
Common Attributes

Refresh your Java programming
The layout_gravity attribute indicates the positions the views should gravitate
towards, while the layout_weight attribute specifies the distribution of
available space
50
Example of Linear Layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:stretchcolumns="*"
>
<Button android:layout_width="100px"
android:layout_height="wrap_content"
android:text="Button A" android:layout_weight="0.1" />
<Button android:layout_width="100px"
android:layout_height="wrap_content"
android:text="Button B" android:layout_gravity="right"
android:layout_weight="0.3" />
<EditText android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textSize="18sp" android:layout_weight="0.6" />
</LinearLayout>
51
Example of Table Layout
<?xml version="1.0" encoding="utf-8"?>
<TableLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_height="fill_parent" android:layout_width="fill_parent"
android:background="#646464">
<TableRow>
<TextView android:text="E-mail:" android:width="120px" />
<EditText android:id="@+id/email" android:width="200px" />
</TableRow>
<TableRow>
<TextView android:text="Password:" />
<EditText android:id="@+id/password" android:password="true" />
</TableRow>
<TableRow>
<TextView />
<CheckBox android:id="@+id/rememberMe" android:text="Remember
Me" /> </TableRow>
<TableRow> <Button android:id="@+id/signIn" android:text="Log In"
android:layout_span="2" /> </TableRow>
</TableLayout>
52
Example of Relative Layout
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:id="@+id/RLayout"
android:layout_width="fill_parent" android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android" >
<TextView android:id="@+id/lblComments"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Comments" android:layout_alignParentTop="true"
android:layout_alignParentLeft="true" />
<EditText android:id="@+id/txtComments"
android:layout_width="fill_parent" android:layout_height="170px"
android:textSize="18sp" android:layout_alignLeft="@+id/lblComments"
android:layout_below="@+id/lblComments"
android:layout_centerHorizontal="true" />
<Button android:id="@+id/btnSave"
android:layout_width="125px" android:layout_height="wrap_content"
android:text="Save" android:layout_below="@+id/txtComments"
android:layout_alignRight="@+id/txtComments" />
<Button android:id="@+id/btnCancel"
android:layout_width="124px" android:layout_height="wrap_content"
android:text="Cancel" android:layout_below="@+id/txtComments"
android:layout_alignLeft="@+id/txtComments" /> </RelativeLayout>
53
Example of Frame Layout
The FrameLayout is a placeholder on screen that you can use to display a
single view
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:id="@+id/RLayout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android" >
<TextView android:id="@+id/lblComments"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello, Android!" android:layout_alignParentTop="true"
android:layout_alignParentLeft="true" />
<FrameLayout android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/lblComments"
android:layout_below="@+id/lblComments"
android:layout_centerHorizontal="true" >
<ImageView android:src = "@drawable/droid"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</FrameLayout> </RelativeLayout>
54
ScrollView



A ScrollView is a special type of FrameLayout in that it enables users to scroll through
a list of views that occupy more space than the physical display
The ScrollView can contain only one child view or ViewGroup, which normally is a
LinearLayout
The ListView is designed for showing a list of related information and is optimized for
dealing with large lists. So, don’t use ListView with ScrollView
<ScrollView android:layout_width=”fill_parent” android:layout_height=”fill_parent”
xmlns:android=”http://schemas.android.com/apk/res/android” >
<LinearLayout android:layout_width=”fill_parent” android:layout_height=”wrap_content”
android:orientation=”vertical” android:focusable=”true”
android:focusableInTouchMode=”true”> <Button android:id=”@+id/button1”
android:layout_width=”fill_parent” android:layout_height=”wrap_content” android:text=”Button 1”
/> <Button android:id=”@+id/button2” android:layout_width=”fill_parent”
android:layout_height=”wrap_content” android:text=”Button 2” /> <Button
android:id=”@+id/button3” android:layout_width=”fill_parent”
android:layout_height=”wrap_content” android:text=”Button 3” />
<EditText android:id=”@+id/txt” android:layout_width=”fill_parent” android:layout_height=”600dp”
/> <Button android:id=”@+id/button4” android:layout_width=”fill_parent”
android:layout_height=”wrap_content” android:text=”Button 4” /> <Button
android:id=”@+id/button5” android:layout_width=”fill_parent”
android:layout_height=”wrap_content” android:text=”Button 5” /> </LinearLayout> </ScrollView> 55
Defining Styles


Multiple Buttons
Define style only once!
...
<TableRow android:id="@+id/TableRow01"
android:layout_weight="0.2"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<Button android:id="@+id/Button07"
style="@style/mybutton" android:text="7" />
<Button android:id="@+id/Button08"
style="@style/mybutton" android:text="8" />
<Button android:id="@+id/Button09"
style="@style/mybutton" android:text="9" />
<Button android:id="@+id/ButtonDivide"
style="@style/mybutton" android:text="/" />
</TableRow>
…
56
Styles in values/styles.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="mybutton"
parent="@android:style/TextAppearance">
<item name="android:textSize">30sp</item>
<item name="android:textColor">#000000</item>
<item name="android:layout_width">fill_parent</item>
<item name="android:layout_height">fill_parent</item>
<item name="android:layout_weight">1</item>
</style>
</resources>
57
Styles and Themes






Way of building and formatting layout to your app
Style has formatting attributes to several elements
The format for the value of the style attribute is as follows: ?[package:][type:]name
Theme has formatting attributes to all activities

Create the theme in xml (styles.xml)

Apply the theme in manifest
To hide the action bar, add android:theme="@android:style/Theme.Holo.NoActionBar"
to AndroidManifest.xml
Hide action bar programmatically
import android.app.ActionBar;
ActionBar actionBar = getActionBar();
actionBar.hide();
//actionBar.show(); //---show it again--58
ActionBar
To add a home button at the ActionBar and move to the main activity when it
is clicked.
case android.R.id.home:
Toast.makeText(this, “You clicked on the Application icon”,
Toast.LENGTH_LONG).show();
Intent i = new Intent(this, MyActionBarActivity.class);
i.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(i);
return true;
The Intent.FLAG_ACTIVITY_CLEAR_TOP flag ensures that the series of
activities in the back stack is cleared when the user clicks the application icon on
the Action Bar. This way, if the user clicks the
back button, the other activities in the application do not appear again.

59
ProgressBar
Add ProgressBar in main.xml
<ProgressBar android:id=”@+id/progressbar”
android:layout_width=”wrap_content”
android:layout_height=”wrap_content”
style=”@android:style/Widget.ProgressBar.Horizontal” />

To display the progress, call its setProgress() method, passing in an integer
indicating its progress

Various ProgressBar styles: Widget.ProgressBar.Horizontal,
Widget.ProgressBar.Small, Widget.ProgressBar.Large,
Widget.ProgressBar.Inverse, Widget.ProgressBar.Small.Inverse,
Widget.ProgressBar.Large.Inverse

60
UI Programmatically






Comment setContentView(R.layout.main); in onCreate()
Specify the layout parameters for the views using LayoutParams object

//---param for views--
LayoutParams params = new
LinearLayout.LayoutParams(LayoutParams.FILL_PARENT,LayoutParams.WRA
P_CONTENT);
The respective layout object should also be created

LinearLayout layout = new LinearLayout(this);

layout.setOrientation(LinearLayout.VERTICAL);
Create TextView and Button and add them to the layout object, using addView()

TextView tv = new TextView(this);

Button btn = new Button(this);

layout.addView(tv); layout.addView(btn);
Create the parameters to be used by the layout
Add the layout to the activity: this.addContentView(layout, layoutParam);
61
Views (Input Controls/Widgets)







TextView

Label
EditText

Editable text
Button

Standard push button
CheckBox

Standard checkbox
RadioButton

Standard radio button
ListView

View group that manages a group of Views.
Spinner

TextView associated with ListView. Let's you select an item from a list.
62
Other Views and Widgets

Widget and Other View
http://developer.android.com/resources/tutorials/views/index.
html

Package android.widget
http://developer.android.com/reference/android/widget/packa
ge-summary.html

view - API Demos (Sample Code)
http://developer.android.com/resources/samples/ApiDemos/sr
c/com/example/android/apis/view/index.html
63
Event Listener (Input Events)






An interface, in the View class, that contains a single callback method
Called by the Android framework when the View is triggered
Multiple EventListeners (Interfaces):

View.OnClickListener - onClick()

View.OnLongClickListener - onLongClick()

View.OnFocusChangeListener - onFocusChange()

View.OnKeyListener - onKey()

View.OnTouchListener - onTouch()

View.OnCreateContextMenuListener - onCreateContextMenu()
When a menu item is selected, onOptionsItemSelected() method is called
The Action Bar populates its action items by calling the
onCreateOptionsMenu() method of an activity
To set a menu in the action bar, use
setShowAsAction(MenuItem.SHOW_AS_ACTION_IF_ROOM)
64
Event Listener (Input Events)
The onCheckedChanged() method can be used with RadioButton and ToggleButton.
CheckBox checkBox = (CheckBox) findViewById(R.id.chkAutosave);
checkBox.setOnClickListener(new View.OnClickListener()
{
public void onClick(View v) {
if (((CheckBox)v).isChecked()) DisplayToast("CheckBox is checked");
else DisplayToast("CheckBox is unchecked");
} });
//---RadioButton--RadioGroup radioGroup = (RadioGroup) findViewById(R.id.rdbGp1);
radioGroup.setOnCheckedChangeListener(new OnCheckedChangeListener()
{
public void onCheckedChanged(RadioGroup group, int checkedId) {
RadioButton rb1 = (RadioButton) findViewById(R.id.rdb1);
if (rb1.isChecked()) { DisplayToast("Option 1 checked!"); }
else { DisplayToast("Option 2 checked!"); }
} });

65
UI Notifications




onKeyDown — Called when a key was pressed and not handled by any of the
views contained within the activity
onKeyUp — Called when a key was released and not handled by any of the
views contained within the activity
onMenuItemSelected — Called when a panel’s menu item has been selected
by the user
onMenuOpened — Called when a panel’s menu is opened by the user
66
Example: onClick() for Button view
public class ExampleActivity extends Activity implements OnClickListener {
protected void onCreate (Bundle savedValues) {
...
Button button = (Button) findViewById(R.id.button_1);
button.setOnClickListener(this);
}
// Implement the OnClickListener callback
public void onClick(View v) {
switch (v.getId()) {
case R.id.button_1:
// do action when the button is clicked
break;
// handle more buttons in the activity
}
}
...
}
67
Views with images





Images could be brought into views using ImageView, Gallery, ImageSwitcher,
GridView
The Gallery is a view that shows items (such as images) in a center-locked,
horizontal scrolling list
The GridView shows items in a two-dimensional scrolling grid. You can use
the GridView together with an ImageView to display a series of images
ImageAdapter class (which extends the BaseAdapter class) is used to bind the
Gallery view with a series of ImageView views. The BaseAdapter class acts as
a bridge between an AdapterView and the data source that feeds data into it.
Examples of AdapterViews are: ListView, GridView, Spinner, Gallery
Subclasses of the BaseAdapter class: ListAdapter, ArrayAdapter,
CursorAdapter, SpinnerAdapter
68
Menus



Options Menu

Compact menu bottom of the screen

Information on current activity
Context Menu

Tap and hold on an element

Information about particular view
Popup Menu

List of items based on the current view
69
Options Menus
// The onCreateOptionsMenu() method is called when the MENU button is pressed.
// When a menu item is selected, the onOptionsItemSelected() method is called
public class MenuExample extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) { ...
}
// Modify menu items dynamically. Disable/enable menu items.
@Override
public boolean onPrepareOptionsMenu(Menu menu) { ...
}
// Create your menu here
@Override
public boolean onCreateOptionsMenu(Menu menu) { ...
}
// When menu item is selected
@Override
public boolean onOptionsItemSelected(MenuItem item) { ...
}
}
70
Creating Menus in XML
(res/menu/menu.xml)
Creating a Menu Resource
<? xml version = "1.0" encoding = "utf-8" ?>
<menu xmlns:android = "http://schemas.android.com/apk/res/android" >
<item android:id = "@+id/new_game"
android:icon = "@drawable/ic_new_game"
android:title = "@string/new_game" />
<item android:id = "@+id/help"
android:icon = "@drawable/ic_help"
android:title = "@string/help" />
</menu>
Inflating a Menu Resource
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu) ;
MenuInflater inflater = getMenuInflater ();
inflater.inflate(R.menu.game_menu, menu );
return true ;
}
71
Responding to Menu Selection
@Override
public boolean onOptionsItemSelected (MenuItem item)
{
// Handle item selection
switch(item.getItemId()) {
case R.id.new_game :
newGame();
return true ;
case R.id.help :
showHelp();
return true ;
default:
return super.onOptionsItemSelected(item);
}
}
72
Changing Menu Dynamically
@Override
public boolean onPrepareOptionsMenu(Menu menu){
super.onPrepareOptionsMenu(menu);
MenuItem menuItem1 = menu.findItem(R.id.new_game);
menuItem1.setEnabled(false);
MenuItem menuItem2 = menu.getItem(0);
menuItem2.setEnabled(false);
return true;
}
73
Submenu
A sub menu can be added within any menu
<? xml version="1.0" encoding="utf-8"?>
<menu xmlns:android = "http://schemas.android.com/apk/res/android" >
<item android:id = "@+id/file"
android:icon = "@drawable/file"
android:title = "@string/file" >
<!-- "file" submenu -->
<menu>
<item android:id = "@+id/create_new"
android:title = "@string/create_new" />
<item android:id = "@+id/open"
android:title = "@string/open" />
</menu>
</item>
</menu>

74
Creating Menus in Java
public class MenuExample extends Activity { // You can increment this for additional menuitems
static final private int MENU_ITEM1 = Menu.FIRST;
static final private int MENU_ITEM2 = Menu.FIRST + 1;
// Create your menu here
@Override
public boolean onCreateOptionsMenu(Menu menu) { super.onCreateOptionsMenu(menu);
// Specify group value to separate Menu Items for batch processing and
// ordering. NONE = No group
int groupId = Menu.NONE;
// Unique identifier for each menu item (used for event handling)
int menuItemId1 = MENU_ITEM1; int menuItemId2 = MENU_ITEM2;
// Order value. Menu.NONE = I don't care
int menuItemOrder = Menu.NONE;
// Menu Text
int menuItemText1 = R.string.menu_item1; int menuItemText2 = R.string.menu_item2;
menu.add(groupId, menuItemId1, menuItemOrder, menuItemText1);
menu.add(groupId, menuItemId2, menuItemOrder, menuItemText2);
// groupId — The group identifier that the menu item should be part of. Use 0 if an item is not in a
Group; itemId — A unique item ID; order — The order in which the item should be displayed; title —
The text to display for the menu item; setAlphabeticShortcut() method can assign shortcut key to
menu item
return true; } }
75
Context Menu




Context Menu = Long press
setOnCreateContextMenuListener() is used to add context menu for an activity
Override two methods on a Activity

onCreateContextMenu(): Called when a user taps and holds the button

onContextItemSelected(): Called when an item inside the context menu is
selected
Register the context menu to the view

registerForContextMenu(view)
For details on menu, and other resources:
http://developer.android.com/guide/topics/resources/availableresources.html
76
Example
public class MyContextMenu extends Activity {
private TextView tv;
@Override
public void onCreate(Bundle savedInstanceState) {
}
@Override
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo) {
}
@Override
public boolean onContextItemSelected(MenuItem item) {
}
}
77
OnCreate
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tv = new TextView(this);
tv.setText("Context Menu!") ;
registerForContextMenu(tv) ;
//or
//tv.setOnCreatContextMenuListener(this);
setContentView(tv);
}
78
OnCreateContextMenu
@Override
public void onCreateContextMenu(ContextMenu menu, View v,
ContextMenuInfo menuInfo)
{
super.onCreateContextMenu(menu, v, menuInfo);
if (v == tv)
{
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.mymenu, menu);
}
}
79
OnContextItemSelected
@Override
public boolean onContextItemSelected(MenuItem item) {
super.onContextItemSelected(item) ;
switch(item.getItemId()){
case R.id.a:
Toast.makeText (this, "A", 1000).show();
return true;
case R.id.b:
Toast.makeText (this, "B", 1000).show();
return true;
}
return false;
}
80
Menus – Summary








Described in XML, stored in res/menu
<menu> has many <item> children
Accessed like other resources (R.menu.<filename>)
onCreateOptionsMenu(Menu menu)

User presses menu button on device
onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo
menuInfo)

User holds down a view (right-clicking/long press)

Need to registerForContextMenu(View v)
onOptionsItemSelected(MenuItem item)

User selects an option from the menu coming from the menu button
onContextItemSelected(MenuItem item)

User selected an option from a context menu
Item.getItemId()

Gets ID of selected item
81
Menus – Summary


<item> elements can also contain other <menu> items!
When <item> is selected, a submenu will open as a context menu
82
Other views
For Clock view, in main.xml:
<AnalogClock
android:layout_width=”wrap_content”
android:layout_height=”wrap_content” />
<DigitalClock
android:layout_width=”wrap_content”
android:layout_height=”wrap_content” />
 WebView: Embed a web browser in your activity
 Handle website redirects within the application itself without
opening the Browser application using
shouldOverrideUrlLoading() method
 Dynamic loading of HTML is done using loadUrl(file:///)

83
User Notification



Toast Notification
 Brief message
Status Bar Notification
 Persistent reminder
Dialog Notification
 Activity-related notification
84
User Notification



Toast appears and disappears in few seconds. Thus, it is better to
use Notifications
A PendingIntent object helps you to perform an action on your
application’s behalf, often at a later time, regardless of whether
your application is running or not.
The getActivity() method retrieves a PendingIntent object and
you set it using the following arguments:
 context — Application context
 request code — Request code for the intent
 intent — The intent for launching the target activity
 flags — The flags in which the activity is to be launched
85
Toast

Toast.makeText(this, "Reset", 1000).show();
86
Status Bar Notification


Adds an icon to the system's status bar
 Expanded message in the notification window
 Optional ticker-text message
 Highly configurable
If your app is working in the background, give status bar
notifications
87
The Basics





Usually a Service is launching the status bar notification
You must use two classes: Notification and NotificationManager
Instance of Notification should have all the information about the
notification (e.g., icon, the expanded message)
NotificationManager is an Android system that executes and
manages all the notifications
You don't instantiate NotificationManager
88
Get Reference to NotificationManager


String ref = Context.NOTIFICATION_SERVICE;
NotificationManager mNotificationManager =
(NotificationManager) getSystemService(ref);
89
Instantiate the Notification

Notification notification = new
Notification(R.drawable.notify_icon, "Hello",
System.currentTimeMillis());
90
Define the Notification’s expanded message and
Intent
Refresh your Java programming
// Communication between status bar and this Activity
Intent notificationIntent = new Intent(this, MyContextMenu.class);
PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
notificationIntent, 0);

notification.setLatestEventInfo(this, "My notification", "Hello
World!", contentIntent);
91
Pass the Notification to the NotificationManager

mNotificationManager.notify(1, notification);
92
Status Bar Notification
String ns = NOTIFICATION_SERVICE;
NotificationManager mNotificationManager = (NotificationManager)
getSystemService(ns);
int icon = R.drawable.icon;
CharSequence tickerText = "Calculator Reseted!";
long when = System.currentTimeMillis();
Notification notification = new Notification(icon, tickerText, when);
Intent notificationIntent = new Intent(this, MyActivity.class);
PendingIntent contentIntent = PendingIntent.getActivity(this, 0, notificationIntent,
0);
notification.setLatestEventInfo(this, "My Calculator", "The calculator was
reseted!", contentIntent);
mNotificationManager.notify(1, notification);
http://developer.android.com/guide/topics/ui/notifiers/notifications.html
93
Dialogs




AlertDialog
ProgressDialog
DatePickerDialog
TimePickerDialog
94
Example of AlertDialog
AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Hello!")
.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
})
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
http://developer.android.com/guide/topics/ui/dialogs.html
95
Example of ProgressDialog


ProgressDialog dialog = ProgressDialog.show(this, "",
"Loading. Please wait...");
dialog.show();
96
Android Logging Options
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The Log.e() method is used to log errors.
The Log.w() method is used to log warnings.
The Log.i() method is used to log informational messages.
The Log.d() method is used to log debug messages.
The Log.v() method is used to log verbose messages.
The Log.wtf() method is used to log terrible failures that should
never happen. ("WTF" stands for "What a Terrible Failure!" of
course.)
 private static final String TAG = "MyApp";
 Log.i(TAG, "I am logging something informational!");
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Debug
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(Window > Open Perspective > Debug)
<application android:icon= "@drawable/icon"
android:label="@string/app_name"
android:debuggable="true" >
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Tools
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DroidDraw:
 http://www.droiddraw.org/
Video:
 http://marakana.com/forums/android/general/212.html
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Recommended to try
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p38: Understanding the Life Cycle of an Activity
p42: Displaying a Dialogue Window using an Activity
p50: Displaying the progress of an operation
p54: Linking Activities with Intents
p130: Understanding Activity Behavior when Orientation Changes
p161: Using the Basic Views
p168: Handling View Events
p191: Displaying a Long List of Items using the ListView
p197: Checking which Items are Selected
p235 Creating the Menu Helper Methods
p238: Displaying an Option Menu
p240: Displaying a Context Menu
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References
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App Development for Smart Devices
 http://www.cs.odu.edu/~cs495/
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