Android Coding

Friday, May 23, 2014

Service LifeCycle

A service is an application component that can run some long running task in the background without the need for a user interface. Some other application component can start the service and this service will then keep on running even if the user switches to another application.

A service can essentially take two forms:

Unbounded
A service is "started" when an application component (such as an activity) starts it by calling startService(). Once started, a service can run in the background indefinitely (unbounded), even if the component that started it is destroyed. Usually, a started service performs a single operation and does not return a result to the caller. For example, it might download or upload a file over the network. When the operation is done, the service should stop itself.

Bound
A service is "bound" when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC). A bound service runs only as long as another application component is bound to it. Multiple components can bind to the service at once, but when all of them unbind, the service is destroyed.

As you can see in diagram there some method in Unbounded service class for life cycle :

startService(Intent Service)
This you must call to start un-bounded serviec

onCreate()
This method is Called when the service is first created

onStartCommand(Intent intent, int flags, int startId)
This method is called when service is started

onBind(Intent intent)
This method you must call if you want to bind with activity

onUnbind(Intent intent)
This method is Called when the service will un-binded from activity

onRebind(Intent intent)
This method is called when you want to Re-bind service after calling un-bind method

onDestroy()
This method is called when The service is no longer used and is being destroyed

Let's create a small app to understand this..

-------------------------------------------
App Name: ServiceLifeCycle
Package Name: com.sunil
Android SDK: Android SDK 2.3.3 / API 10
Default Activity Name: MyActivity
-------------------------------------------

MyActivity.java

package com.sunil;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MyActivity extends Activity
implements OnClickListener {
private final static String TAG = "In this method: ";
private Button startSerivce = null;
private Button stopSerivce = null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
startSerivce = (Button) findViewById(R.id.buttonStart);
startSerivce.setOnClickListener(this);
stopSerivce = (Button) findViewById(R.id.buttonStop);
stopSerivce.setOnClickListener(this);
}
@Override
public void onClick(View v) {
if (startSerivce == v) {
Log.i(TAG, "Activity starting service..");
Intent serviceIntent = new Intent(this, MyService.class);
startService(serviceIntent);
} else {
Intent in = new Intent(this, MyService.class);
in.setAction("stop");
stopService(in);
}
}
}

MyService

package com.sunil;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;
import android.widget.Toast;
public class MyService extends Service {
private final static String TAG = "In this method: ";
int mStartMode; // indicates how to behave if the service is killed
IBinder mBinder; // interface for clients that bind
boolean mAllowRebind; // indicates whether onRebind should be used
@Override
public void onCreate() {
Log.i(TAG, "Service created");
// The service is being created
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.i(TAG, "Service started");
Toast.makeText(getBaseContext(), "Service has been started..",
Toast.LENGTH_SHORT).show();
return mStartMode;
}
@Override
public IBinder onBind(Intent intent) {
// A client is binding to the service with bindService()
Log.i(TAG, "Service binded");
return mBinder;
}
@Override
public boolean onUnbind(Intent intent) {
// All clients have unbound with unbindService()
Log.i(TAG, "Service un-binded");
return mAllowRebind;
}
@Override
public void onRebind(Intent intent) {
// A client is binding to the service with Re-bindService(),
// after onUnbind() has already been called
Log.i(TAG, "Service re-binded");
}
@Override
public void onDestroy() {
// The service is no longer used and is being destroyed
Log.i(TAG, "Service destroyed");
}
}

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:gravity="center">
<LinearLayout
android:layout_height="wrap_content"
android:layout_width="match_parent"
android:id="@+id/linearLayout1"
android:gravity="center">
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:id="@+id/buttonStart"
android:text="Start Service"></Button>
<Button
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:id="@+id/buttonStop"
android:text="Stop Serivce"></Button>
</LinearLayout>
</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest
xmlns:android="http://schemas.android.com/apk/res/android"
package="com.sunil"
android:versionCode="1"
android:versionName="1.0">
<uses-sdk android:minSdkVersion="8" />
<application
android:icon="@drawable/icon"
android:label="@string/app_name">
<activity
android:name=".MyActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service
android:enabled="true"
android:name=".MyService">
<intent-filter>
<action android:name="com.sunil.MyService">
</action>
</intent-filter>
</service>
</application>
</manifest>

The output Screen will be like this..

You can download the complete source code zip file here : ServiceLifeCycle

Activity Lifecycle

I’m just starting with Android App Development, and if you are a beginner like me, you probably want to understand two of main concepts of Android: Activities and Intents.

After Hello World Example i wanted to know Activity Life-cycle so i learn this and sharing with you..
This is the Android Activity Life Cycle Diagram described by Google

As you can see in diagram there 7 method in activity base class for life cycle :
onCreate(Bundle savedInstanceState)
This method is Called when the activity is first created.

onStart()
This method is Called when activity is becoming visible to the user.

onResume()
This method is Called when the activity will start interacting with the user.

onPause()
This method is Called when the system is about to start resuming a previous activity.

onStop()
This method is Called when the activity is no longer visible to the user, because another activity has been resumed and is covering this one.

onRestart()
This method is Called after your activity has been stopped, prior to it being started again.

onDestroy()
This method is The final call you receive before your activity is destroyed.

Other Methods:
onSaveInstanceState(Bundle outState)
This method is called before an activity may be killed so that when
it comes back some time in the future it can restore its state.

onRestoreInstanceState(Bundle savedInstanceState)
This method is called after onStart() when the activity is being
re-initialised from a previously saved state.
The default implementation of this method performs a restore of any
view state that had previously been frozen by onSaveInstanceState(Bundle).

Create a simple android app with default activity "MyActivity" then put the code like this

package com.sunil;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;
public class MyActivity extends Activity {
private final static String TAG="In this method: ";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Toast.makeText(this, "onCreate", Toast.LENGTH_SHORT).show();
Log.i(TAG,"Activity created");
}
@Override
protected void onStart() {
super.onStart();
Toast.makeText(this, "onStart",Toast.LENGTH_SHORT).show();
Log.i(TAG,"Activity started and visible to user");
}
@Override
protected void onResume() {
super.onResume();
Toast.makeText(this, "onResume", Toast.LENGTH_SHORT).show();
Log.i(TAG,"Activity interacting with user");
}
@Override
protected void onPause() {
super.onPause();
Toast.makeText(this, "onPause", Toast.LENGTH_SHORT).show();
Log.i(TAG,"current activity got paused");
}
@Override
protected void onStop() {
super.onStop();
Toast.makeText(this, "onStop", Toast.LENGTH_SHORT).show();
Log.i(TAG," current activity got stopped");
}
@Override
protected void onRestart() {
super.onRestart();
Toast.makeText(this, "onRestart", Toast.LENGTH_SHORT).show();
Log.i(TAG,"activity again restarted");
}
@Override
protected void onDestroy() {
super.onDestroy();
Toast.makeText(this, "onDestroy", Toast.LENGTH_SHORT).show();
Log.i(TAG,"activity destored");
}
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Toast.makeText(getBaseContext(),"onSaveInstanceState..BUNDLING",
Toast.LENGTH_SHORT).show();
Log.i(TAG,"activity data saved");
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
Toast.makeText(getBaseContext(), "onRestoreInstanceState ..BUNDLING",
Toast.LENGTH_SHORT).show();
Log.i(TAG,"activity previous saved data restored");
}
}

and main.xml is

<linearlayout android:layout_height="fill_parent" android:layout_width="fill_parent" android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android">
<textview android:layout_height="wrap_content" android:layout_width="fill_parent" android:text="Activity Life Cycle.." android:textsize="20sp">
</textview></linearlayout>

the most important is AndroidManifest.xml

<manifest android:versioncode="1" android:versionname="1.0" package="com.sunil" xmlns:android="http://schemas.android.com/apk/res/android">
<uses-sdk android:minsdkversion="8">
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:label="@string/app_name" android:name=".MyActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN">
<category android:name="android.intent.category.LAUNCHER">
</category></action></intent-filter>
</activity>
</application>
</uses-sdk></manifest>

you can find the example zip file is here

ListView in Android (Basic)

ListView: ListView is a view group that displays a list of scrollable items. The list items are automatically inserted to the list using an Adapter that pulls content from a source such as an array and converts each item result into a view that's placed into the list.

This tutorial describes how to use ListView and ListActivity in Android.

okay! so let's try this small app

-------------------------------------------
App Name: ListViewBasic
Package Name: com.sunil
Android SDK: Android SDK 2.3.3 / API 10
Default ListActivity Name: ActivityListView
-------------------------------------------

ActivityListView.java

    package com.sunil;   

    import android.app.ListActivity;  

    import android.os.Bundle;  

    import android.view.View;  

    import android.widget.ArrayAdapter;  

    import android.widget.ListView;  

    import android.widget.Toast;  

    public class ActivityListView extends ListActivity {

     public void onCreate(Bundle savedInstanceState) {  

     super.onCreate(savedInstanceState);  

     // Create an array of Strings, that will be put to our ListActivity  

     String[] namesArray = new String[] { "Linux", "Windows7", "Eclipse",  

        "Suse", "Ubuntu", "Solaris", "Android", "iPhone" };  

     /* Create an ArrayAdapter, that will actually make the Strings above 

      appear in the ListView */ 

     this.setListAdapter(new ArrayAdapter<String>(this,  

       android.R.layout.simple_list_item_1, namesArray));  

     } 

      @Override  

      protected void onListItemClick(ListView l, View v,   

      int position, long id) {  

     super.onListItemClick(l, v, position, id);  

     // Get the item that was clicked  

     Object o = this.getListAdapter().getItem(position);  

     String keyword = o.toString();  

     Toast.makeText(this, "You selected: " + keyword,   

       Toast.LENGTH_SHORT).show();  

     }  

    }