Download Android App Basics

Android App Basics
Slides from developer.android.com and adopted from Janzen
Android Architecture
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Android built on Linux 2.6 kernel
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What is a kernel?
Provides security, memory management, process
management, network stack, and driver model
Abstraction layer between hardware and the software
stack
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Android Architecture
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A set of C/C++ libraries exposed to developers through the
application framework
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System C library - a BSD-derived implementation of the standard
C system library (libc), tuned for embedded Linux-based devices
Media Libraries - based on PacketVideo's OpenCORE; the libraries
support playback and recording of many popular audio and video
formats, as well as static image files, including MPEG4, H.264, MP3,
AAC, AMR, JPG, and PNG
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Android Architecture
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A set of C/C++ libraries exposed to developers through
the application framework
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Surface Manager - manages access to the display subsystem
and seamlessly composites 2D and 3D graphic layers from
multiple applications
FreeType - bitmap and vector font rendering
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Android Architecture

A set of C/C++ libraries exposed to developers through
the application framework
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LibWebCore - a modern web browser engine which powers
both the Android browser and an embeddable web view
SGL - the underlying 2D graphics engine
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Android Architecture
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A set of C/C++ libraries exposed to developers through the
application framework
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3D libraries - an implementation based on OpenGL ES 1.0 APIs; the
libraries use either hardware 3D acceleration (where available) or
the included, highly optimized 3D software rasterizer
SQLite - a powerful and lightweight relational database engine
available to all applications
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Android Architecture
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Runtime libraries provide most of the functionality in the
core Java libraries
Each app has a process and an instance of Dalvik VM
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Uses Dalvik Executable (.dex) format – low memory footprint
VM is register based runs compiled Java classes
The linux kernel provides Dalvik with needed functionality
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Android Architecture
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Named for Dalvik in Iceland, a fishing village where
ancestors of Dan Bornstein lived.
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Dalvik is discontinued process virtual machine as of Android
version 4.4 (KitKat)
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The successor of Dalvik is Android Runtime (ART), which
uses the same bytecode and .dex files, aiming at performance
improvements transparent to end users.
I
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Android Architecture
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The framework allows developers to build cool apps
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Android Architecture
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Set of services and systems
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Views to build apps: lists, grids, text boxes, buttons, browser
Content providers enable apps to share data between each
other
Resource manager for access to non-code resources such as
localized strings, graphics, and layout files
A Notification manager that enables all applications to display
custom alerts in the status bar
Activity manager manages lifecycle of apps and provides a
common navigation backstack
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Views
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Basic block for a UI component, occupying a rectangle on
the screen
It draws and handles events
Widgets – interactive UI components
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Buttons, text fields, spinners, date picker, map,etc.
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Views
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ViewGroup – ways to group other views
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Layouts – invisible containers holding views and define properties
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Android Architecture
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Core applications ship with android.
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Resources
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Value
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Strings, colors, dimensions, arrays (strings, integers, typed), bool, ID,
Drawable – something drawn to the screen
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Bitmaps, NinePatch (stretchable) images
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Layout
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Property – modify object’s property values over time
Tween – rotate, move, stretch, and fade a view
Frame – to display a sequence of images
Color State List – change color based on state
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Layouts define the look of your activity, can specify in XML or with code, XML often easier
Animations
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PNG is preferred, JPG, and GIF supported
Example: button is pressed, focused, or neither, define color for each
Menu – defines app menu (options, context, submenu, …) that can be inflated
Style – defines the format and look of a UI for view or activity
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Application Fundamentals
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Written in Java, using Android SDK to compile into an
Android Package
Each app lives in its own security sandbox (principle of
least privilege: only access to what it needs)
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Android OS is multi-user with each app a user
Each app gets a user ID
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Can be shared between apps (also share same process and VM)
Each process has own VM – runs in isolation
Each app has its own process – started for any component
Can request permission to access device data (SMS, camera…)
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Granted at install time
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Application Components
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Intents and Intent Filters
Activities
Services
Content Providers
Broadcast Receivers
App Widgets
Processes and Threads
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Intents and Intent Filters
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Intents and Intent Filters
An Intent is a messaging object you can use to request an action from another app
component. Intents (an asynchronous message) are used to start components
(except content providers)
 Content providers are activated when targeted by a request from a
ContentResolver. Call query() on a ContentResolver to query a content
Provider
 Start Activity - An Activity represents a single screen in an app.You can start a
new instance of an Activity by passing an Intent to startActivity().
 Start Service - A Service is a component that performs operations in the
background without a user interface.You can start a service to perform a onetime operation (such as download a file) by passing an Intent to startService().
 Deliver Broadcast - A broadcast is a message that any app can receive. The
system delivers various broadcasts for system events, such as when the system
boots up or the device starts charging.You can deliver a broadcast to other apps
by passing an Intent to sendBroadcast(), sendOrderedBroadcast(), or
sendStickyBroadcast().
An Intent filter specifies the types of intents that an activity, service, or broadcast
receiver can respond to. An intent filter declares the capabilities of its parent
component.
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Activities
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Activities
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A single screen with a user interface
Example – text message screen, inbox, compose email, etc.
They are independent
An app may have more than one
Typically, one activity in an application is specified as the "main"
activity, which is presented to the user when launching the
application for the first time.
Can be started by other applications (if allowed)
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Activities
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Activities
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Fragments - A Fragment represents a behavior or a portion of user
interface in an Activity. You can combine multiple fragments in a single
activity to build a multi-pane UI and reuse a fragment in multiple
activities.
Loaders – They make it easy to asynchronously load data in an
activity or fragment. They are available to every Activity and
Fragment. Monitor the source of their data and deliver new results
when the content changes
Tasks and Back Stack - A task is a collection of activities that users
interact with when performing a certain job. The activities are
arranged in a stack (the "back stack"), in the order in which each
activity is opened. When the user presses the Back button, the
current activity is popped from the top of the stack (the activity is
destroyed) and the previous activity resumes (the previous state of
its UI is restored). Activities in the stack are never rearranged, only
pushed and popped from the stack
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Services
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Services
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Runs in the background for long-running operations or remote
processes
Has no user interface
Example – play music, fetch data
An activity can start a service, or bind to a service for
interaction.
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Content Providers
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Content Providers
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Manages a shared set of application data
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Stored in the file system, an SQLite database, on the web, any other
persistent location you have access to
Other apps can query or modify data (if allowed)
Example: contact information
Can also be used for private app data
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Broadcast Receivers
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Broadcast Receivers
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Responds to system-wide broadcasts
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No user interface but may create a status bar notification
Generally a gateway to other components and light weight
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i.e. start a service to perform work based on an event
Any application can start another application’s component
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Generally originate from system, i.e. low battery, screen off, picture taken.
Apps can also broadcast, i.e. data ready for use
Will start a process for the component’s app, not run in yours
Means no single entry point (i.e main())
You can’t start it, need to have system deliver a message with your
intent to start a component
Makes it much easier to add functionality to your app
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App Widgets
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App Widgets are miniature application views that can be
embedded in other applications (such as the Home
screen) and receive periodic updates. These views are
referred to as Widgets in the user interface, and you can
publish one with an App Widget provider.
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Processes and Threads
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When an application component starts and the application
does not have any other components running, the Android
system starts a new Linux process for the application with a
single thread of execution. By default, all components of the
same application run in the same process and thread (called
the "main" thread).
If an application component starts and there already exists a
process for that application (because another component from
the application exists), then the component is started within
that process and uses the same thread of execution.
You can arrange for different components in your application
to run in separate processes, and you can create additional
threads for any process.
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Manifest
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Each app has an AndroidManifest.xml file
Declare all the components in this file
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Identify user permissions required by app (ie internet
access, rw contacts,…)
Declare minimum API level required
Declare hardware and software features used or required
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In root of app project directory
i.e camera, bluetooth services, camera, multitouch screen
API libraries needed by app for linking
And more
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An example
Adapted from Janzen
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A First Example: Advent Devotions
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UML Class Diagram
External Activity
Generated by Android
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Two Activities in Advent Devotions
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AdventDevos displays the
calendar of dates
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Devo displays a single
devotion
Intent myIntent = new Intent(AdventDevos.this, Devo.class);
myIntent.putExtra("ButtonNum", "" + index);
startActivity(myIntent);
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Two Activities in Advent Devotions
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AdventDevos displays the
calendar of dates
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Devo displays a single
devotion
Bundle extras = getIntent().getExtras();
String value = extras.getString("ButtonNum");
Integer buttonNum = Integer.valueOf(value);
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Launching an Intent you didn’t
write
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Devos has button to URL
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Browser launched
Intent i = new Intent(Intent.ACTION_VIEW,
Uri.parse("http://www.biblegateway.com/passage/?search="+
passage +"&version=NIV"));
startActivity(i);
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Android Activity
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“An activity is a single, focused thing that the user can do.
Almost all activities interact with the user, so the Activity
class takes care of creating a window for you in which
you can place your UI with setContentView(View).”
http://developer.android.com/reference/android/app/
Activity.html#ActivityLifecycle
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Android Manifest.xml
http://developer.android.com/guide/topics/manifest/manifest-intro.html
<?xml version="1.0" encoding="utf-8"?> Each upload to PlayStore requires versionCode incremen
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.simexusa.adventdevotions"
android:versionCode="2"
Specifies icon for launching app
android:versionName="1.0">
<application android:icon="@drawable/star" android:label="@string/app_name" android:debuggable="false">
<activity android:name=".AdventDevos"
android:label="@string/app_name">
Specifies icon label for launching app
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:name=".Devo"/>
</application>
Specifies activity to be launched at startup
<uses-sdk android:minSdkVersion=“19" />
<uses-permission android:name="android.permission.INTERNET" />
</manifest>
SDK version required by app
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Security permissions requested from user on install
Layouts and Resources
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See main.xml and devo.xml
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Activity associates with layout xml file using
setContentView(R.layout.main); or
setContentView(R.layout.devo); in onCreate()
Note TableLayout and TableRow similar to <table> and <tr> in
html
Note use of dimen (see values/dimens.xml) and color (see
values/colors.xml)
Also see strings.xml
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main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:background="@color/background">
<TableLayout android:layout_width="wrap_content"
android:id="@+id/TableLayout01" android:layout_height="wrap_content">
<TableRow android:paddingTop="8px">
<Button android:text="Nov. 29" android:id="@+id/Button01"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:textSize="@dimen/button_width"></Button>
<Button android:text="Nov. 30" android:id="@+id/Button02"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:textSize="@dimen/button_width"></Button>
<Button android:text="Dec. 1" android:id="@+id/Button03"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:textSize="@dimen/button_width"></Button>
<Button android:text="Dec. 2" android:id="@+id/Button04"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:textSize="@dimen/button_width"></Button>
</TableRow> …
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devo.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:gravity="center_horizontal"
android:background="@color/background">
<TextView android:text="Date" android:id="@+id/Date"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:gravity="center_horizontal" android:textStyle="italic"
android:textSize="@dimen/reference_width" android:typeface="serif"
android:textColor="@color/text"></TextView>
<TextView android:text="Title" android:id="@+id/Title"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:gravity="center_horizontal" android:textStyle="bold"
android:textSize="@dimen/reference_width" android:typeface="serif"
android:textColor="@color/text"></TextView>
<Button android:text="Read Scripture" android:id="@+id/ButtonScripture"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:gravity="center_horizontal"
android:textSize="@dimen/reference_width"></Button>
<ScrollView android:id="@+id/ScrollView01"
android:layout_height="fill_parent" android:layout_width="fill_parent">
<TextView android:text="Body" android:id="@+id/Body"
android:layout_width="wrap_content" android:layout_height="wrap_content"
android:gravity="left" android:textSize="@dimen/reference_width"
android:typeface="serif" android:textColor="@color/text"></TextView>
</ScrollView>
</LinearLayout>
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dimens.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<dimen name="button_width">17sp</dimen>
<dimen name="reference_width">20sp</dimen>
</resources>
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colors.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="background">#AAFFFF99</color>
<color name="text">#FF000000</color>
</resources>
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strings.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<string name="hello">Hello World,
AdventDevos!</string>
<string name="app_name">Advent
Devotions</string>
</resources>
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Attributes and their Meaning
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Resources
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All Apps have resources (non-code)
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Can update app characteristics without modifying code
Can have device dependent resources
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Different hardware capabilities
Can have user dependent resources
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Images, audio, animations, menus, styles, colors, layouts…
Languages, preferences, etc
Each resource has unique integer ID
Use a qualifier to decide which set of resources to use
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Portrait vs landscape
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Android Application Lifecycle
and Menus
Adapted from Janzen
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Except as otherwise noted, the content of this presentation is
licensed under the Creative Commons Attribution 2.5 License.
Application Lifecycle
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Look at Application Fundamentals
http://developer.android.com/guide/topics/fundamentals.html
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Active lifetime
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Visible lifetime
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has focus, accepting UI events
onResume to onPause
Visible, but does not have focus
onStart to onStop
Full lifetime
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onCreate to onDestroy
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Process Lifecycle
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Processes keep around for as long as possible, will kill less important
processes
Foreground activity at top of screen user interacting with - most
important.
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Visible activity is visible to user but not in foreground, is
extremely important
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Only killed if required to keep the foreground activity running.
Background activity is not visible (paused) so not critical,
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Only killed if out of memory
System may kill to reclaim memory for foreground or visible processes.
If user navigates back to activity, onCreate(Bundle) called
Empty process is hosting no components.
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Killed very quickly as memory becomes low.
Background operations executed in BroadcastReceiver or Service to
keep process around.
http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle
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Active Lifetime Example
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Campus Maps App
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Shows user location on campus map image
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http://market.android.com/search?q=pname:com.simexusa.campusmaps_full
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Active Lifetime Example
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Campus Maps
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Turn on/off GPS to save battery when UI not in focus
@Override
protected void onPause() {
super.onPause();
//stop receiving GPS and Orientation data
locationManager.removeUpdates(locationListener);
}
@Override
protected void onResume() {
super.onResume();
//restart receiving GPS and Orientation data
locationManager.requestLocationUpdates(provider, 2000, 10,
locationListener);
}
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Visible Lifetime Example
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Campus Maps
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Save state as app could get killed after onStop()
@Override
protected void onStop() {
super.onStop();
savePreferences();
}
@Override
protected void onStart() {
super.onStart();
restoreUIState();
}
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Visible Lifetime Example
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Campus Maps
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Save state as app could get killed after onStop()
private void savePreferences() {
SharedPreferences cmSharedPreferences =
getSharedPreferences(CMPREFS,Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = cmSharedPreferences.edit();
editor.putBoolean(VIRTUAL_MODE, inVirtualMode);
editor.putInt(MAP_INDEX, curMapIndex);
editor.commit();
}
private void restoreUIState() {
SharedPreferences cmSharedPreferences =
getSharedPreferences(CMPREFS,Activity.MODE_PRIVATE);
inVirtualMode = cmSharedPreferences.getBoolean(VIRTUAL_MODE, true);
curMapIndex = cmSharedPreferences.getInt(MAP_INDEX, 0);
}
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UI Elements
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View
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Control
ViewGroup
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Layout
Widget (Compound Control)
Many expected Views
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Button, CheckBox, RadioButton
TextView, EditText, ListView
Can be customized by extending and overriding onDraw()
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XML UI Configuration
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Layouts can specify UI elements (provided and custom)
res/layout
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Menus
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Icon Menu (up to 6 icons)
Expanded Menu (from More on Icon Menu)
Submenus
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Activity lifecycle
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Active or running
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Paused
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Visible but lost focus
Stopped
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Top of stack
In foreground of screen
Obscured by another activity
No longer visible, but keeps
state
Dead
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If paused or stopped can be
killed or asked to finish
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Must be restarted
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Activity lifecycle
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Called when fist created
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Static setup
Create views, bind data, …
Provides Bundle
containing activity’s
previously frozen state, if
there was one
Always followed by
onStart()
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Activity lifecycle
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Called after activity has
been stopped, prior to it
being restarted
Followed by onStart()
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Activity lifecycle
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Called when activity
becomes visible to user
Followed by onResume()
if activity comes to the
foreground or onStop() if
becomes hidden
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Activity lifecycle
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Called when activity will
start interacting with user
Activity now on top of
activity stack, with user
input going to it.
Followed by onPause()
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Activity lifecycle
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Called when system about
to start resuming a previous
activity.
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Use to commit unsaved
changes to persistent data,
stop animations, and anything
else consuming CPU
Needs to be very quick
since next activity will not
resume until done
Followed by OnResume()
(activity returns back to
front) or onStop()
(becomes invisible)
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Activity lifecycle
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Called when the activity
is no longer visible
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Another activity covering
it
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New activity started
Existing activity moved to
front
This one being destroyed
Followed by onRestart()
(activity coming back for
interaction) or
onDestroy() (going away)
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Activity lifecycle
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Final call before being
destroyed
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Activity finished (finish()
called)
Destroyed by system to
save space
Use isFinishing() to figure
out which
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App ideas for Project
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Ringer in Vibrate mode based on Calendar notifications
Roll Taker using the Camera
Sync events on multiple different Calendars
Developing useful widgets
Shopping app with nice features (camera, barcode support)
Deal Monitoring app
Weather reporter
International student app (TAMUCC or just CS)
Paint mixer
Islander game, lane based attack, islander theme (tiki)
Humans and Zombies
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