Download What is an Android “app”

Write Your First
Android App
9/3/2014
About Me
● EveryLabs
○ Co-founder & Android Lead
● Mustbin
○ Software Architect & Android Lead
● RunKeeper
○ Lead Android Developer
● Professional Android Sensor Development
○ co-author
Agenda
● Go over some app basics
● Write a simple “Hello Android” app
● Walk through a more complicated app
What is an Android “app”
● Package of Android components
● Resources used by those Android
Components
● Usually written in Java
● Distributed in an APK
● Runs on Android
Components of an Android App
●
●
●
●
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Activity
ContentProvider
Service
BroadcastReceiver
Most apps won’t use all four, but all apps will
use some
Activity
● Represents a “screen” in the app
● Well defined lifecycle
● UI can be specified in XML or code
ContentProvider
●
●
●
●
Abstracts database access
Well supported in Android
Cumbersome at times
Highly recommended
○ A bit of a “holy war”
Service
● Not associated with a screen
○ Background task
● (Usually) runs on the UI thread
● (Usually) runs in same process as rest of
app
BroadcastReceiver
● Handles broadcasts
○ System-wide
○ In-app
■ LocalBroadcastReceiver
● Asynchronous
● May not persist in memory through
subsequent executions
Intents
● The “glue” that ties Android components
together
○ Starts Activities
○ Starts Services
○ Launches BroadcastReceivers
● System-wide messages
● Components can declare Intent filters
● Passes data between components
Implicit vs Explicit Intents
● Explicit
○ Start component by name
○ “Start Activity MyCameraActivity.class”
● Implicit
○ Declare an action
○ “Start an Activity that can take a picture”
Back Stack
● Apps usually contain a stack of Activities
○ “Back Stack”
Source: https://developer.android.com/guide/components/tasks-and-back-stack.html
Back Stack
● Apps can contain activities from other apps
○ This allows developers to include functionality from
other apps directly into theirs
Task
● A collection of Activities
● Capable of being moved into the background
○ Pressing home button
○ All activities in Task are stopped
■ Activities can be destroyed if they are not visible
and the system needs resources
Source: https://developer.android.com/guide/components/tasks-and-back-stack.html
How apps “live” in Android
● Installed as a different user in Android
○ Android is a multi-user Linux OS
● Each app has it’s own home directory
○ Private from other apps (unless device is rooted)
● Apps run in their own process
● An app is uniquely identified by it’s “package
name”
App Execution
● By default, all app components run in the
same process and thread.
○ Referred to as the “main” or “UI” thread
● Main thread dispatches events to UI widgets
● Android will NOT tolerate long operations of
the main thread
○ The OS will kill an app if it blocks the main
thread
App Execution
● Worker threads can perform long tasks
● All UI manipulation MUST happen on the
main thread
○ A runtime exception will be thrown otherwise
● The Android SDK provides support for long
running tasks
○ AsyncTask
○ Loaders
Activity Lifecycle
Source: https://developer.android.com/training/basics/activity-lifecycle/starting.html
Activity Lifecycle
● onCreate()
○
○
○
○
Called once per instance
Load layout
Initialization
Not visible
● onStart()
○ Becomes visible
Activity Lifecycle
● onResume()
○ Activity in foreground
● onPause()
○ Activity no longer in foreground, but visible
■ Blocked by dialog
● onStop()
○ Activity not visible
Activity Lifecycle
● onDestroy()
○ Activity is going away
○ onCreate() will be called again if Activity is needed
later
Defining the UI for an Activity
● Hierarchy of
Views and
ViewGroups
● Usually defined
in XML
● Can also use
Java code
Source: https://developer.android.com/training/basics/firstapp/building-ui.html
ViewGroup
● Organizes views on the screen
● Consists of views and other ViewGroups
● Layouts
○
○
○
○
LinearLayout
RelativeLayout
FrameLayout
GridView
LinearLayout
● Positions children
in a single
direction
○ Vertical
○ Horizontal
Source: https://developer.android.com/guide/topics/ui/layout/linear.html
RelativeLayout
● Positions children
relative to each
other
○
○
○
○
Source: https://developer.android.com/guide/topics/ui/layout/relative.html
“Left Of”
“Right Of”
“Below”
“Above”
GridView
● Arranges children in a
grid
Source: https://developer.android.com/guide/topics/ui/layout/gridview.html
Views
●
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EditText
TextView
Button
RadioButton
CheckBox
XML Layout Example
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin">
<TextView
android:text="@string/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</RelativeLayout>
Associating XML layout in Activity
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_hello_world);
}
“R” class
● auto-generated by the Android tools
● Provides access to app resources
○
○
○
○
Strings
Layouts
Misc. values
Drawables (images)
Android Project Structure (Gradle)
● app
○ main app
● app/src/main/java
○ Java code
● app/src/main/res
○ app resources
Resource Qualifiers
● Provides different variations of
same resource
● Android will select proper
resource at runtime
Resource Qualifier Examples
●
●
●
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Screen size
Screen density
Android version
Language
Android Manifest
● Contains meta-data about app
○ Components
○ Permissions
○ Features
■ camera
■ GPS
○ Minimum Android version
○ Launcher Activity
○ Package name
Manifest Example
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.adstrosoftware.tsw">
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_SYNC_SETTINGS" />
<uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS_SYNC_SETTINGS" />
<uses-permission android:name="android.permission.AUTHENTICATE_ACCOUNTS" />
<application
android:name=".Application"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme">
<activity
android:name=".NotesActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
Manifest Example
<activity
android:name="com.evernote.client.android.EvernoteOAuthActivity"
android:configChanges="orientation|keyboardHidden" />
<provider
android:name=".provider.TswProvider"
android:authorities="com.adstrosoftware.tsw.provider"
android:exported="false" />
<service
android:name="com.adstrosoftware.tsw.sync.AuthenticatorService">
<intent-filter>
<action android:name="android.accounts.AccountAuthenticator"/>
</intent-filter>
<meta-data
android:name="android.accounts.AccountAuthenticator"
android:resource="@xml/authenticator" />
</service>
</application>
</manifest>
Hello Android App
●
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Android Studio
Gradle
JDK (6 or 7)
Genymotion
○ Emulation replacement
○ Much faster
Where to go from here
● Android developer docs
○ https://developer.android.com/index.html
● Android design
○ https://developer.android.com/design/index.html
○ https://developer.android.
com/preview/material/index.html
Code and Contact Info
Email: [email protected]
Twitter: @adstro
Slides: http://goo.gl/A5WyRH
https://github.com/adstro/hello-android
https://github.com/adstro/reading-list
Attribution
Portions of this presentation are reproduced
from work created and shared by the Android
Open Source Project and used according to
terms described in the Creative Commons 2.5
Attribution License.
Questions?