Intents can also be used to send broadcast messages into the Android system. BroadcastReceivers can register to event and will get notified if such an event is triggered.

Your application can register to system events, e.g. a new email has arrived, system boot is complete or a phone call is received and react accordingly.

As said earlier, since Android version 3.1 the Android system will per default exclude all BroadcastReceiver from receiving Intents if the corresponding application has never been started by the user or if the user explicitly stopped the application via the Android menu (in Manage Application).

Sometimes you want to find if an application has registered for a certain Intent. For example you want to check if a certain receiver is available and if you enable some functionality in your app.

This can be done via the PackageManager class. The following code checks if an someone has registered himself for a certain Intent. Construct your Intent as you desired to trigger it and pass it to the following method.

public static boolean isIntentAvailable(Context ctx, Intent intent) {
   final PackageManager mgr = ctx.getPackageManager();
   List<ResolveInfo> list =
      mgr.queryIntentActivities(intent, 
         PackageManager.MATCH_DEFAULT_ONLY);
   return list.size() > 0;
} 

Based on the result you can adjust your application for example you could disable or hide certan menu items.

The following assumes that you have already basic knowledge in Android development. Please check the Android development tutorial to learn the basics.

The following tutorial demonstrates how to use explicit Intents and how to transfer data between two activities.

The first activity will call the second one via an explicit intent. Once the user select the "Back" button on his phone the first activity will receive some hard-coded data from the Sub-Activity.

Create a new Android application "de.vogella.android.intent.explicit" with the activity called ActivityOne.

Change the layout main.xml to the following.

<?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/TextView01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:minHeight="60dip"
        android:text="First Activity. Press button to call second activity"
        android:textSize="20sp" >
    </TextView>

    <Button
        android:id="@+id/Button01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onClick"
        android:text="Calling an intent" >
    </Button>

</LinearLayout> 

Create the layout "activity_result.xml".

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:alignmentMode="alignBounds"
    android:columnCount="2"
    android:columnOrderPreserved="false"
    android:useDefaultMargins="true" >

    <TextView
        android:layout_gravity="center_horizontal"
        android:text="Input 1"
        android:textSize="32dip" />

    <EditText
        android:id="@+id/input1"
        android:layout_gravity="fill_horizontal"
        android:text="Default" />

    <TextView
        android:layout_gravity="center_horizontal"
        android:text="Input 2"
        android:textSize="32dip" />

    <EditText
        android:id="@+id/input2"
        android:layout_gravity="fill_horizontal"
        android:text="Default" />

 
    <Button
        android:layout_column="1"
        android:layout_gravity="right"
        android:width="80dp"
        android:onClick="onClick"
        android:text="Finish" />

</GridLayout> 

Declare a new activity called ActivityTwo via the AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.intent.explicit"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

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

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name="ActivityTwo"
            android:label="ActivityTwo" >
        </activity>
    </application>


</manifest> 

Create the following coding for your two activities.

package de.vogella.android.intent.explicit;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;

public class ActivityOne extends Activity {
  private static final int REQUEST_CODE = 10;

  
/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
  }

  public void onClick(View view) {
    Intent i = new Intent(this, ActivityTwo.class);
    i.putExtra("Value1", "This value one for ActivityTwo ");
    i.putExtra("Value2", "This value two ActivityTwo");
    // Set the request code to any code you like, you can identify the
    // callback via this code
    startActivityForResult(i, REQUEST_CODE);
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
      if (data.hasExtra("returnKey1")) {
        Toast.makeText(this, data.getExtras().getString("returnKey1"),
            Toast.LENGTH_SHORT).show();
      }
    }
  }
} 

package de.vogella.android.intent.explicit;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class ActivityTwo extends Activity {

  
/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.second);
    Bundle extras = getIntent().getExtras();
    if (extras == null) {
      return;
    }
    String value1 = extras.getString("Value1");
    String value2 = extras.getString("Value2");
    if (value1 != null && value2 != null) {
      EditText text1 = (EditText) findViewById(R.id.input1);
      EditText text2 = (EditText) findViewById(R.id.input2);
      text1.setText(value1);
      text2.setText(value2);
    }
  }

  public void onClick(View view) {
    finish();
  }

  @Override
  public void finish() {
    Intent data = new Intent();
    // Return some hard-coded values
    data.putExtra("returnKey1", "Swinging on a star. ");
    data.putExtra("returnKey2", "You could be better then you are. ");
    setResult(RESULT_OK, data);
    super.finish();
  }
} 

Run your application. The first will send data to the second activity which will be shown on the user interface. If you select back on your phone, the first activity will display a Toast with the data from the second activity.

The following exercise demonstrates the usage of implicit intents to trigger activities in your Android system.

Create a new Android application called de.vogella.android.intent.implicit with an activity called CallIntentsActivity.

In this example you use a Spinner view to select which intent is triggered. For the content of the Spinner you define static values.

Create the following intents.xml file in the res/values folder.

<resources>
    <string-array name="intents">
        <item>Open Browser</item>
        <item>Call Someone</item>
        <item>Dial</item>
        <item>Show Map</item>
        <item>Search on Map</item>
        <item>Take picture</item>
        <item>Show contacts</item>
        <item>Edit first contact</item>
    </string-array>
    
</resources> 

Change the layout file of the Activity to the following.

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:alignmentMode="alignBounds"
    android:columnCount="1" >

      <Spinner
        android:id="@+id/spinner"
        android:layout_gravity="fill_horizontal"
        android:drawSelectorOnTop="true"
        >
      </Spinner>
    
    <Button
        android:id="@+id/trigger"
        android:onClick="onClick"
        android:text="Trigger Intent">
    </Button>

  
</GridLayout> 

To be able to use certain intents you need to register for the required permission in your AndroidManifest.xml file. Ensure that your AndroidManifest.xml contain the permissions from the followng listing.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.intent.implicit"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

    <uses-permission android:name="android.permission.CALL_PRIVILEGED" >
    </uses-permission>
    <uses-permission android:name="android.permission.CALL_PHONE" >
    </uses-permission>
    <uses-permission android:name="android.permission.CAMERA" >
    </uses-permission>
    <uses-permission android:name="android.permission.READ_CONTACTS" >
    </uses-permission>
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:name=".CallIntentsActivity"
            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>

</manifest> 

Change your activity class to the following code.

package de.vogella.android.intent.implicit;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;

public class CallIntentsActivity extends Activity {
  private Spinner spinner;

  
/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    spinner = (Spinner) findViewById(R.id.spinner);
    ArrayAdapter adapter = ArrayAdapter.createFromResource(this,
        R.array.intents, android.R.layout.simple_spinner_item);
    adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
    spinner.setAdapter(adapter);
  }

  public void onClick(View view) {
    int position = spinner.getSelectedItemPosition();
    Intent intent = null;
    switch (position) {
    case 0:
      intent = new Intent(Intent.ACTION_VIEW,
          Uri.parse("http://www.vogella.com"));
      break;
    case 1:
      intent = new Intent(Intent.ACTION_CALL,
          Uri.parse("tel:(+49)12345789"));
      break;
    case 2:
      intent = new Intent(Intent.ACTION_DIAL,
          Uri.parse("tel:(+49)12345789"));
      startActivity(intent);
      break;
    case 3:
      intent = new Intent(Intent.ACTION_VIEW,
          Uri.parse("geo:50.123,7.1434?z=19"));
      break;
    case 4:
      intent = new Intent(Intent.ACTION_VIEW,
          Uri.parse("geo:0,0?q=query"));
      break;
    case 5:
      intent = new Intent("android.media.action.IMAGE_CAPTURE");
      break;
    case 6:
      intent = new Intent(Intent.ACTION_VIEW,
          Uri.parse("content://contacts/people/"));
      break;
    case 7:
      intent = new Intent(Intent.ACTION_EDIT,
          Uri.parse("content://contacts/people/1"));
      break;

    }
    if (intent != null) {
      startActivity(intent);
    }
  }

  @Override
  public void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == Activity.RESULT_OK && requestCode == 0) {
      String result = data.toURI();
      Toast.makeText(this, result, Toast.LENGTH_LONG);
    }
  }

} 

If you start your application you see an list of buttons and if you press one of the buttons, your defined activities are started.

In the following exercise you register an activity as browser, i.e. for the intent which is triggered if someone want to view an URL starting with http.

The example activity downloads the HTML source of this page and display this in a TextView.

Create the Android project called de.vogella.android.intent.browserfilter with the activity called BrowserActivity.

Register your activity to Intent.Action_VIEW action and the scheme "http" via the following changes in your AndroidManifest.xml file The manifest also declares the permission to access the Internet.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="de.vogella.android.intent.browserfilter"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="15" />

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

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <activity
            android:name=".BrowserActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />

                <category android:name="android.intent.category.DEFAULT" />

                <data android:scheme="http" />
            </intent-filter>
        </activity>
    </application>

</manifest> 

Change corresponding layout file to the following.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    >
<TextView  
    android:layout_width="match_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/textView"/>
</LinearLayout> 

Change your activity class to the following code.

package de.vogella.android.intent.browserfilter;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.os.StrictMode;
import android.widget.TextView;

public class BrowserActivity extends Activity {
  
/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // To keep this example simple, we allow network access
    // in the user interface thread
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder()
        .permitAll().build();
    StrictMode.setThreadPolicy(policy);

    setContentView(R.layout.main);
    Intent intent = getIntent();
    TextView text = (TextView) findViewById(R.id.textView);
    // To get the action of the intent use
    String action = intent.getAction();
    if (!action.equals(Intent.ACTION_VIEW)) {
      throw new RuntimeException("Should not happen");
    }
    // To get the data use
    Uri data = intent.getData();
    URL url;
    try {
      url = new URL(data.getScheme(), data.getHost(), data.getPath());
      BufferedReader rd = new BufferedReader(new InputStreamReader(url.openStream()));
      String line = "";
      while ((line = rd.readLine()) != null) {
        text.append(line);
      }

    } catch (Exception e) {
      e.printStackTrace();
    }

  }
} 

Install your application. If you now trigger an intent to open an URL your should be able to select your own component. You can for example trigger this intent via the example from the implicit tutorials.

If you select you component the HTML code is loaded into your text view.

The following example shows how to pick an image from any registered photo application on Android via an intent.

Create a new Android project called de.vogella.android.imagepick with one activity called ImagePickActivity.

Change the activity_main.xml layout file to the following.

<?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" >

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="pickImage"
        android:text="Button" >
    </Button>

    <ImageView
        android:id="@+id/result"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:src="@drawable/icon" >
    </ImageView>

</LinearLayout> 

Change your activity class according to the following coding.

package de.vogella.android.imagepick;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;

public class ImagePickActivity extends Activity {
  private static final int REQUEST_CODE = 1;
  private Bitmap bitmap;
  private ImageView imageView;

  
/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    imageView = (ImageView) findViewById(R.id.result);
  }

  public void pickImage(View View) {
    Intent intent = new Intent();
    intent.setType("image/*");
    intent.setAction(Intent.ACTION_GET_CONTENT);
    intent.addCategory(Intent.CATEGORY_OPENABLE);
    startActivityForResult(intent, REQUEST_CODE);
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    InputStream stream = null;
    if (requestCode == REQUEST_CODE && resultCode == Activity.RESULT_OK)
      try {
        // We need to recyle unused bitmaps
        if (bitmap != null) {
          bitmap.recycle();
        }
        stream = getContentResolver().openInputStream(data.getData());
        bitmap = BitmapFactory.decodeStream(stream);

        imageView.setImageBitmap(bitmap);
      } catch (FileNotFoundException e) {
        e.printStackTrace();
      } finally {
        if (stream != null)
          try {
            stream.close();
          } catch (IOException e) {
            e.printStackTrace();
          }
      }
  }
} 

If you run this application you can select an image from your image library on your Android phone and assign it to your ImageView.

Please help me to support this article:

Before posting questions, please see the vogella FAQ. If you have questions or find an error in this article please use the www.vogella.com Google Group. I have created a short list how to create good questions which might also help you.