5. INTENT

Intents allow sending or receiving data from and to other activities or services. Intents are objects of type "android.content.Intent" and are used to send asynchronous messages within your application or between applications.Intents can also be used to broadcast to the Android system that a certain event has occurred. Other components in Android can register to this event and will get notified.

Intents are a powerful concept as they allow the creation of loosely coupled applications. Intents can be used to communicate between any installed application component on the device.

An Intent object can contain information for the receiving component. For example if your application calls via an Intent a browser it may send the URL to the browser component. An Intent also contain information for the Android system so that the Android system can determine which component should handle the request.

5.1 IMPLICIT vs. EXPLICIT

Android supports explicit intents and implicit intents.

Implicit intents asked the system to perform a service without telling the system which Java class should do this service. In constructing an implicit Intent you specify the action which should be performed and optionally an URI which should be used for this action. For example you could tell the system that you want to view (action) a webpage (URI). By starting an intent for this data the system would try to find an application which is registered for this event, e.g. a browser.

Intent intent = new Intent(Intent.ACTION_DIAL);

Explicit intent names the component, e.g. the Java class which should be called. i.e, in explicit intent we define from and to, from which activity , to which activity- here the second activity to which we navigate is given as .class. We should add the second java page in manifest file while using explicit intent.

Intent intent = new Intent(FirstActivity.this, second.class );

5.2 STARTING ACTIVITIES

For an Intent to work i.e., to perform the action the above given code is insufficient. We need to call a method startActivity(intent) along with above code. startActivity(intent) is called only when you don’t expect a value from called activity.

If suppose you have a return value from called activity then instead of startActivity(intent) we use startActivityForResult(intent) . After the called activity is finished the program returns to a sub activity called onActivityResult() which is implemented while programming.

In some cases you might want to pass data from activity to other. This can be done by using method putExtras(). This method contains two parts/argument we could say. One is key value the second is string value/data to be passed. To get the information fin the called activity use getIntent() along with getExtras(). By using getString(key) we could extract the data. Also you can make use of Bundle for passing data. When using Bundle we put data in Bundle using putExtras() and Bundle in Intent.

5.3 IMPLICIT INTENT

Example- xml page

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/hello" />

<Button

android:id="@+id/bttn1"

android:text=" call "

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

<Button

android:id="@+id/bttn2"

android:text=" sms "

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

<Button

android:id="@+id/bttn3"

android:text=" internet "

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

First activity page

package a.b.c;

import android.app.Activity;

import android.content.Intent;

import android.net.Uri;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

public class ImplicitintentActivity extends Activity {

Button b1,b2,b3;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

b1 = (Button)findViewById(R.id.bttn1);

b1.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {

// TODO Auto-generated method stub

Intent i = new Intent(Intent.ACTION_CALL, Uri.parse("tel:5556"));

startActivity(i);

}

});

b2 = (Button)findViewById(R.id.bttn2);

b2.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {

// TODO Auto-generated method stub

Intent i = new Intent(Intent.ACTION_SENDTO, Uri.parse("sms:5556"));

startActivity(i);

}

});

b3 = (Button)findViewById(R.id.bttn3);

b3.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {

// TODO Auto-generated method stub

Intent i = new Intent(Intent.ACTION_VIEW, Uri.parse("http://www.google.com"));

startActivity(i);

}

});

}

5.4 EXPLICIT INTENT

Example 1- first activity

package a.b.c;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;

public class ExplicitintentActivity extends Activity {

Button b1;

EditText e1;

String s1;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

e1 = (EditText)findViewById(R.id.ed1);

b1 = (Button)findViewById(R.id.bttn1);

b1.setOnClickListener(new OnClickListener() {

public void onClick(View v) {

// TODO Auto-generated method stub

s1 = e1.getText().toString();

Intent i = new Intent(ExplicitintentActivity.this, secondPage.class);

Bundle b = new Bundle();

b.putString("k", s1);

i.putExtras(b);

startActivity(i);

}

});

}

First xml page

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="@string/hello" />

<EditText

android:id="@+id/ed1"

android:layout_width="120dip"

android:layout_height="wrap_content"/>

<Button

android:id="@+id/bttn1"

android:text=" Go to second page "

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

Second activity page

package a.b.c;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.widget.TextView;

import android.widget.Toast;

public class secondPage extends Activity {

TextView t1;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main1);

t1 = (TextView)findViewById(R.id.tv1);

Intent in = getIntent();

Bundle bu = in.getExtras();

String s = bu.getString("k");

t1.setText(s);

Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();

}

Second xml page

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical" >

<TextView

android:id="@+id/tv1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

Manifest file- In this we should add the second java page/activity as shown below. In manifest we should add all activities which we are using in application

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="a.b.c"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk android:minSdkVersion="10" />

<application

android:icon="@drawable/ic_launcher"

android:label="@string/app_name" >

<activity

android:label="@string/app_name"

android:name=".ExplicitintentActivity" >

<intent-filter >

</intent-filter>

</activity>

</application>

</manifest>

5.5 STARTAVTICITYFORRESULT

Example 2 – using method startActivityFor Result()

First activity page

package a.b.c;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class Startactivity4rsltActivity extends Activity {

Button b1;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

b1 = (Button)findViewById(R.id.bttn1);

b1.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View arg0) {

// TODO Auto-generated method stub

Intent i = new Intent(Startactivity4rsltActivity.this, second.class);

startActivityForResult(i, 0);

}

});

}

@Override

protected void onActivityResult(int requestCode, int resultCode, Intent data) {

// TODO Auto-generated method stub

super.onActivityResult(requestCode, resultCode, data);

Bundle bundle = data.getExtras();

String s = bundle.getString("k");

Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();

}

Main xml page

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="fill_parent"

android:layout_height="fill_parent"

android:orientation="vertical" >

<TextView

android:layout_width="fill_parent"

android:layout_height="wrap_content"

android:text="START ACTIVITY FOR RESULT"

android:textSize="20dip" />

<Button

android:id="@+id/bttn1"

android:text=" GO "

android:textSize="20dip"

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

Second activity page

package a.b.c;

import android.app.Activity;

import android.content.Intent;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

public class second extends Activity {

Button b2;

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main1);

b2 = (Button)findViewById(R.id.bttn2);

b2.setOnClickListener(new OnClickListener() {

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

Intent intent = new Intent();

Bundle b = new Bundle();

b.putString("k", "DONE");

intent.putExtras(b);

setResult(RESULT_OK, intent);

finish();

}

});

}

Main1 xml page

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical" >

<TextView

android:text="Enter you name"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:textSize="35dip"/>

<EditText

android:layout_width="140dip"

android:layout_height="wrap_content"

android:layout_marginTop="20dip"/>

<Button

android:id="@+id/bttn2"

android:text=" Ok "

android:layout_width="wrap_content"

android:layout_height="wrap_content"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

package="a.b.c"

android:versionCode="1"

android:versionName="1.0" >

<uses-sdk android:minSdkVersion="10" />

<application

android:icon="@drawable/ic_launcher"

android:label="@string/app_name" >

<activity

android:label="@string/app_name"

android:name=".Startactivity4rsltActivity" >

<intent-filter >

</intent-filter>

</activity>

</application>

</manifest>

Remember that whenever we add an Activity to our application it should be added in manifest file.

Android

Monday, May 21, 2012

INTENTS full note

5. INTENT

5.1 IMPLICIT vs. EXPLICIT

5.2 STARTING ACTIVITIES

5.3 IMPLICIT INTENT

5.4 EXPLICIT INTENT

5.5 STARTAVTICITYFORRESULT

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