Android activity, service, and broadcast recievers

Hello Android

1. Create a new project by – file -> New Project -> Android Project.
2. Enter the details -
Project Name – HelloWorld
Build Target – Android 2.2 (API 8)
Application Name – Hello Android
Package name – cdac.android.helloworld
Activity name – HelloWorldActivity
3. Click o finish, and wait for the project to be created.
4. The build your project.
5. Then click o the play icon In the taskbar on the top, or right click on the project
folder In the workspace, and then select – android application
6. Select the AVD corresponding to the build target, and then wait for the
emulator to load

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Select AVD

New Project

3

Understanding Hello world
Android Project file structure
Project Name

1.Src
2.Gen
3.Android version Libraries
4.Assets
5.Res
- drawable-hdpi
-drawable-ldpi
-drawable-mdpi
-layout
-values
6.AndroidManifest.xml
7.Default.properties

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Brief Description about the Folders

Src an assets folder

This src folder, contains the actual source code

Res and assets folder

The Resource aka res folder, contains all the resource files which are divided into
generally 5 folders

a. drawable – hdpi
b drawable – ldpi
c. drawable – mdpi
d. layout
e. values

Apart from all other files are added to the assets folder like java projects,

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The gen folder

The gen folder contains the file R.java.
This file is auto generated
R.Java contains set of unique
precompiled IDs assigned to every
resource in the res folder.

The default.properties file

This file generally contains the
information regarding the version of
Android used to make the application.
But, in order to specify or change the
build environment or parameters we’ll
modify this file

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AndroidManifest. xml

The manifest lets you define the structure and metadata of your application, its
components, and its requirements.

Breaking down

1. Activity tag – To describe any new activity in the application

2. Application, intent-filter tag

<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".DatePickerActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>

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3. Android Permissions (uses-application tag)

The Android permissions are the set of hardware/software permissions to be
taken by the current application.

<uses-permission android:name="android.permission.INTERNET" />

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Android Activity

An Activity is an application
component that provides a screen
with which users can interact in
order to do something, such as dial
the phone, take a photo, send an
email, or view a map.

The very first step in developing an
Android application is making a
Activity
Your application must have at least
one Activity.

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Importance of Activity

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 .

While activities are often presented to the user as full-screen windows, they can
also be used in other ways: as floating windows or embedded inside of another
activity (using ActivityGroup).

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Creating an Activity

To create an activity, you must create a subclass of Activity (or an existing
subclass of it). In your subclass, you need to implement the most important
callback methods are:

onCreate()
The system calls this when creating your activity.

Most importantly, this is where you must call setContentView() to define the
layout for the activity's user interface.

onPause()
This is usually where we should commit any changes that should be persisted
beyond the current user session (because the user might not come back).

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Dissection of an Activity
Some of the important overridden methods in the Activity Class
1.onStart();
2.onRestart();
3.onResume();
4.onPause();
5.onStop();
6.onDestroy();
7.void finish();
8.void finishActivity(int requestCode);
9.setContentView(int layoutResID);
10.void setTitle(CharSequence title)
11.startActivity(Intent intent)
12.setIntent(Intent newIntent)
13.View findViewById(int id) ;
14.PendingIntent createPendingResult(int requestCode, Intent data, int flags);
15.Boolean onKeyEvent(KeyEvent event);
16.boolean onTouchEvent(MotionEvent ev);
17.boolean onTrackballEvent(MotionEvent ev);

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1. LayoutInflater getLayoutInflater()
2. WindowManager getWindowManager()
3. Window getWindow()
4. Dialog onCreateDialog(int id)
5. boolean onCreatePanelMenu(int featureId, Menu menu)
6. View onCreatePanelView(int featureId)
7. Boolean onCreateThumbnail(Bitmap outBitmap, Canvas canvas)
8. View onCreateView(String name, Context context, AttributeSet attrs)
9. boolean onMenuItemSelected(int featureId, MenuItem item)
10. startSearch(String initialQuery, boolean selectInitialQuery,Bundle appSearchData,
boolean globalSearch)
11. startIntentSender(IntentSender intent, Intent fillInIntent,int flagsMask, int
flagsValues, int extraFlags)
12. boolean startActivityIfNeeded(Intent intent, int requestCode)

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Activity Life Cycle

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Summary of Activity Life cycle

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Android Service

A Service is an application component that can perform long-running operations in
the background and does not provide a user interface.

Additionally, a component can bind to a service to interact with it and even perform
interprocess communication (IPC).

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Broadcast Receivers

A broadcast receiver is a class which extends "BroadcastReceiver" and which is
registered as a receiver in an Android Application via the AndroidManifest.xml (or
via code). This class will be able to receive intents via the sendBroadcast() method.

Broadcast receiver is a component that responds to system-wide broadcast
announcements

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References

1. http://developer.android.com/reference/android/app/Activity.html
2. http://developer.android.com/reference/android/app/Service.html
3. http://developer.android.com/reference/android/content/BroadcastReceiver.html

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Android activity, service, and broadcast recievers

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