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Android Intents - Tutorial

Lars Vogel

Version 3.4

21.02.2014

Revision History
Revision 0.1 - 3.4 20.07.2010 - 21.02.2014 Lars
Vogel
bug fixes and enhancements

Using Intents in Android

This tutorials describes the usage of intents to communicate between Android components. It is based on Eclipse 4.3, Java 1.6 and Android 4.3.


Table of Contents

1. Intents and intent filter
1.1. What are intents?
1.2. Starting activities
1.3. Sub-activities
1.4. Starting services
2. Intents types
2.1. Different types of intents
2.2. Explicit Intents
2.3. Implicit Intents
3. Data transfer between activities
3.1. Data transfer to the target component
3.2. Example: Using the share intent
3.3. Retrieving result data from a sub-activity
4. Defining intent filters
4.1. Intent filter
4.2. Defining intent filter
4.3. Example: Register an activity as browser
4.4. Example: Register an activity for the share intent
5. Intents as event triggers
6. Determine valid intent receivers
7. Prerequisites for this tutorial
8. Exercise: Starting activities
8.1. Target of this exercise
8.2. Create project and main layout
8.3. Create new layout file
8.4. Create additional activity
8.5. Start sub-activity
8.6. Send data to ResultActivity
8.7. Get intent data in the ResultActivity
9. Exercise: Receiving data from sub-activities
9.1. Target of this exercise
9.2. Return data from ResultActivity
9.3. Evaluate the return data in MainActivity
10. Solution: Using intents
10.1. How to use this chapter
10.2. Activity code
11. Exercise: Using different implicit intents
12. Exercise: Register an intent filter for HTTP requests
13. Exercise: picking an image via an intent
14. Support free vogella tutorials
14.1. Thank you
14.2. Questions and Discussion
15. Links and Literature
15.1. Source Code
15.2. Android Resources
15.3. vogella Resources

1. Intents and intent filter

1.1. What are intents?

Intents are asynchronous messages which allow application components to request functionality from other Android components. Intents allow you to interact with components from the same applications as well as with components contributed by other applications. For example, an activity can start an external activity for taking a picture.

Intents are objects of the android.content.Intent type. Your code can send them to the Android system defining the components you are targeting. For example, via the startActivity() method you can define that the intent should be used to start an activity.

An intent can contain data via a Bundle. This data can be used by the receiving component.

1.2. Starting activities

To start an activity, use the method startActivity(intent). This method is defined on the Context object which Activity extends.

Start activity via an intent

The following code demonstrates how you can start another activity via an intent.

# Start the activity connect to the
# specified class

Intent i = new Intent(this, ActivityTwo.class);
startActivity(i); 

1.3. Sub-activities

Activities which are started by other Android activities are called sub-activities. This wording makes it easier to describe which activity is meant.

1.4. Starting services

You can also start services via intents. Use the startService(Intent) method call for that.

2. Intents types

2.1. Different types of intents

Android supports explicit and implicit intents.

An application can define the target component directly in the intent (explicit intent) or ask the Android system to evaluate registered components based on the intent data (implicit intents).

2.2. Explicit Intents

Explicit intents explicitly define the component which should be called by the Android system, by using the Java class as identifier.

The following shows how to create an explicit intent and send it to the Android system. If the class specified in the intent represents an activity, the Android system starts it.

Intent i = new Intent(this, ActivityTwo.class);
i.putExtra("Value1", "This value one for ActivityTwo ");
i.putExtra("Value2", "This value two ActivityTwo"); 

Explicit intents are typically used within on application as the classes in an application are controlled by the application developer.

2.3. Implicit Intents

Implicit intents specify the action which should be performed and optionally data which provides content for the action.

For example, the following tells the Android system to view a webpage. All installed web browsers should be registered to the corresponding intent data via an intent filter.

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

If an implicit intent is sent to the Android system, it searches for all components which are registered for the specific action and the fitting data type.

If only one component is found, Android starts this component directly. If several components are identified by the Android system, the user will get a selection dialog and can decide which component should be used for the intent.

A component can register itself for actions. See Section 4.1, “Intent filter” for details.

3. Data transfer between activities

3.1. Data transfer to the target component

An intent contains certain header data, e.g., the desired action, the type, etc. Optionally an intent can also contain additional data based on an instance of the Bundle class which can be retrieved from the intent via the getExtras() method.

You can also add data directly to the Bundle via the overloaded putExtra() methods of the Intent objects. Extras are key/value pairs. The key is always of type String. As value you can use the primitive data types (int, float, ...) plus objects of type String, Bundle, Parceable and Serializable.

The receiving component can access this information via the getAction() and getData() methods on the Intent object. This Intent object can be retrieved via the getIntent() method.

The component which receives the intent can use the getIntent().getExtras() method call to get the extra data. That is demonstrated in the following code snippet.

Bundle extras = getIntent().getExtras();
if (extras == null) {
  return;
}
// get data via the key
String value1 = extras.getString(Intent.EXTRA_TEXT);
if (value1 != null) {
  // do something with the data
} 

3.2. Example: Using the share intent

Lots of Android applications allow you to share some data with other people, e.g., the Facebook, G+, Gmail and Twitter application. You can send data to one of these components. The following code snippet demonstrates the usage of such an intent within your application.

// this runs, for example, after a button click
Intent intent = new Intent(Intent.ACTION_SEND);
intent.setType("text/plain");
intent.putExtra(android.content.Intent.EXTRA_TEXT, "News for you!");
startActivity(intent); 

3.3. Retrieving result data from a sub-activity

An activity can be closed via the back button on the phone. In this case the finish() method is performed. If the activity was started with the startActivity(Intent) method call, the caller requires no result or feedback from the activity which now is closed.

If you start the activity with the startActivityForResult() method call, you expect feedback from the sub-activity. Once the sub-activity ends, the onActivityResult() method on the sub-activity is called and you can perform actions based on the result.

In the startActivityForResult() method call you can specify a result code to determine which activity you started. This result code is returned to you. The started activity can also set a result code which the caller can use to determine if the activity was canceled or not.

startActivity with result

startActivity with result

The sub-activity uses the finish() method to create a new intent and to put data into it. It also sets a result via the setResult() method call.

The following example code demonstrates how to trigger an intent with the startActivityForResult() method.

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);
} 

If you use the startActivityForResult() method, then the started activity is called a sub-activity.

If the sub-activity is finished, it can send data back to its caller via an Intent. This is done in the finish() method.

@Override
public void finish() {
  // Prepare data intent 
  Intent data = new Intent();
  data.putExtra("returnKey1", "Swinging on a star. ");
  data.putExtra("returnKey2", "You could be better then you are. ");
  // Activity finished ok, return the data
  setResult(RESULT_OK, data);
  super.finish();
} 

Once the sub-activity finishes, the onActivityResult() method in the calling activity is called.

@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();
    }
  }
} 

4. Defining intent filters

4.1. Intent filter

Intents are used to signal to the Android system that a certain event has occurred. Intents often describe the action which should be performed and provide data upon which such an action should be done. For example, your application can start a browser component for a certain URL via an intent. This is demonstrated by the following example.

String url = "http://www.vogella.com";
Intent i = new Intent(Intent.ACTION_VIEW);
i.setData(Uri.parse(url));
startActivity(i); 

But how does the Android system identify the components which can react to a certain intent?

A component can register itself via an intent filter for a specific action and specific data. An intent filter specifies the types of intents to which an activity, service, or broadcast receiver can respond to by declaring the capabilities of a component.

Android components register intent filters either statically in the AndroidManifest.xml or in case of a broadcast receiver also dynamically via code. An intent filter is defined by its category, action and data filters. It can also contain additional meta-data.

If an intent is sent to the Android system, the Android platform runs a receiver determination. It uses the data included in the intent. If several components have registered for the same intent filter, the user can decide which component should be started.

4.2. Defining intent filter

You can register your Android components via intent filters for certain events. If a component does not define one, it can only be called by explicit intents. This chapter gives an example for registering a component for an intent. The key for this registration is that your component registers for the correct action, mime-type and specifies the correct meta-data.

If you send such an intent to your system, the Android system determines all registered Android components for this intent. If several components have registered for this intent, the user can select which one should be used.

4.3. Example: Register an activity as browser

The following code will register an Activity for the Intent which is triggered when someone wants to open a webpage.

<activity android:name=".BrowserActivitiy" 
          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> 

4.4. Example: Register an activity for the share intent

The following example registers an activity for the ACTION_SEND intent. It declares itself only relevant for the text/plain mime type.

<activity
  android:name=".ActivityTest"
    android:label="@string/app_name" >
    <intent-filter>
      <action android:name="android.intent.action.SEND" />
      
      <category android:name="android.intent.category.DEFAULT" />

      <data android:mimeType="text/plain" />
    
    </intent-filter>

</activity> 

If a component does not define an intent filter, it can only be called by explicit intents.

5. Intents as event triggers

Intents can be used to send broadcast messages into the Android system. A broadcast receiver can register to an event and is notified if such an event is sent.

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.

6. Determine valid intent receivers

Sometimes you want to determine if a component has registered for an intent. For example, you want to check if a certain intent receiver is available and in case a component is available, you enable a functionality in your application.

This check can be done via the PackageManager class.

The following example code checks if a component has registered for a certain intent. Construct your intent as you are 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 certain menu items.

7. Prerequisites for this tutorial

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

8. Exercise: Starting activities

8.1. Target of this exercise

The following exercise demonstrates how to use an explicit intent to start a sub-activity and how to send data to it.

This is the first part of an exercise continued in ???. The final solution can be found in ???.

8.2. Create project and main layout

Create a new Android project called com.vogella.android.intent.explicit with an activity called MainActivity.

Change the layout file of this activity to the following.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <EditText
        android:id="@+id/inputforintent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:minHeight="60dip"
        android:text="First Activity"
        android:textSize="20sp" >
    </EditText>

    <Button
        android:id="@+id/startintent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/inputforintent"
        android:layout_below="@+id/inputforintent"
        android:onClick="onClick"
        android:text="Calling an intent" />

</RelativeLayout> 

8.3. Create new layout file

Create a new layout called activity_result.xml. In the next step you create a new activity which will use this layout file.

To create a new layout file, select your project, right click on it and select FileNewOther...AndroidAndroid XML File and select the Layout option.

Enter activity_result.xml as file name and press the Finish button. Change your layout so that it is similar to the following XML file.

<?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/displayintentextra"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Input"
       />

    <EditText
        android:id="@+id/returnValue"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <requestFocus />
    </EditText>

</LinearLayout> 

8.4. Create additional activity

Add a new activity called ResultActivity to the AndroidManifest.xml file.

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

    <uses-sdk android:minSdkVersion="14" />

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

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

</manifest> 

Create the corresponding ResultActivity class based on the following example code.

package com.vogella.android.intent.explicit;

import android.app.Activity;
import android.os.Bundle;

public class ResultActivity extends Activity {

  @Override
  public void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.activity_result);
  }
} 

Note

This new activity will be started via the MainActivity, hence it is called a sub-activity.

8.5. Start sub-activity

Start the sub-activity via a button click from the MainActivity class. The following code gives some pointers on how to solve this. Solve the TODO's in the source code so that the ResultActivity activity is started from the onClick() method.

package com.vogella.android.intent.explicit;

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

public class MainActivity extends Activity {

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }

  public void onClick(View view) {
    EditText text = (EditText) findViewById(R.id.inputforintent);
    // used later
    String value = text.getText().toString();
    // TODO 1 create new Intent(context, class)
    // use the activity as context parameter
    // and "ResultActivity.class" for the class parameter

    // TODO 2 start second activity with
    // startActivity(intent);
  }

} 

Once you finished this part of the exercise, start your application and ensure that you can start the second activity.

8.6. Send data to ResultActivity

The MainActivity class should pass the value of the EditText view to the sub-activity. For this use the putExtra("yourKey", string) on the Intent object.

8.7. Get intent data in the ResultActivity

In your ResultActivity sub-activity get the Bundle with the intent data via the getIntent().getExtras()) method call.

Get the value of the passed extra with the extras.getString("yourkey") method on the bundle object which you got with the getExtras() call.

This value should be placed in the TextView with the displayintentextra ID.

9. Exercise: Receiving data from sub-activities

9.1. Target of this exercise

This is the second part of an exercise which started in Section 8.1, “Target of this exercise”. An example solution for the activity can be found in Section 10, “Solution: Using intents”.

Continue to use the com.vogella.android.intent.explicit project.

In the following exercise you transfer data back from your second sub-activity to the MainActivity once the user selects the Back button.

9.2. Return data from ResultActivity

Add the implementation of the finish() method to the ResultActivity class.

@Override
public void finish() {
    
  // TODO 1 create new Intent 
  // Intent intent = new Intent();
    
  // TODO 2 read the data of the EditText field
  // with the id returnValue
  
  // TODO 3 put the text from EditText
  // as String extra into the intent
  // use editText.getText().toString();
    
  // TODO 4 use setResult(RESULT_OK, intent); 
  // to return the Intent to the application
  
  super.finish();
} 

Solve all TODOs.

9.3. Evaluate the return data in MainActivity

Use the startActivityForResult() method in MainActivity to start the sub-activity. This allows you to use the onActivityResult() method to receive data from the sub-activity. Extract the extra data with the received bundle.

Show a Toast with the extra data to validate that you correctly received it. The following code contains some pointer on how to solve that.

package com.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 MainActivity extends Activity {
  
  // constant to determine which sub-activity returns
  private static final int REQUEST_CODE = 10;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }

  public void onClick(View view) {
    EditText text = (EditText) findViewById(R.id.inputforintent);
    String string = text.getText().toString();
    Intent i = new Intent(this, ResultActivity.class);
    i.putExtra("yourkey", string);
    // TODO 2.. now use 
    // startActivityForResult(i, REQUEST_CODE);
  }

  // TODO 3 Implement this method
  // assumes that "returnkey" is used as key to return the result
  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
      if (data.hasExtra("returnkey")) {
        String result = data.getExtras().getString("returnkey");
        if (result != null && result.length() > 0) {
          Toast.makeText(this, result, Toast.LENGTH_SHORT).show();
        }
      }
    }
  }
} 

10. Solution: Using intents

10.1. How to use this chapter

After finishing the exercise in Section 9.1, “Target of this exercise”, your activity coding should look similar to the following classes.

You can use this chapter to compare your solution with the proposed solution.

10.2. Activity code

package com.vogella.android.intent.explicit;

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

public class ResultActivity extends Activity {

  @Override
  public void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.activity_result);
    Bundle extras = getIntent().getExtras();
    String inputString = extras.getString("yourkey");
    TextView view = (TextView) findViewById(R.id.displayintentextra);
    view.setText(inputString);
  }

  @Override
  public void finish() {
    Intent intent = new Intent();
    EditText editText= (EditText) findViewById(R.id.returnValue);
    String string = editText.getText().toString();
    intent.putExtra("returnkey", string);
    setResult(RESULT_OK, intent);
    super.finish();
  }
} 

package com.vogella.android.intent.explicit;

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

public class MainActivity extends Activity {

  // constant to determine which sub-activity returns
  private static final int REQUEST_CODE = 10;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
  }


  public void onClick(View view) {
    EditText text = (EditText) findViewById(R.id.inputforintent);
    String string = text.getText().toString();
    Intent i = new Intent(this, ResultActivity.class);
    i.putExtra("yourkey", string);
    startActivityForResult(i, REQUEST_CODE);
  }

  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (resultCode == RESULT_OK && requestCode == REQUEST_CODE) {
      if (data.hasExtra("returnkey")) {
        String result = data.getExtras().getString("returnkey");
        if (result != null && result.length() > 0) {
          Toast.makeText(this, result, Toast.LENGTH_SHORT).show();
        }
      }
    }
  }
} 

11. Exercise: Using different implicit intents

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 the 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 contains the permissions from the following 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 a list of buttons and if you press one of the buttons, your defined activities are started.

Note

Note that you didn't specify any receiving application, only the action that should be done. This allows you to define loosely coupled tasks which use components of different applications.

12. Exercise: Register an intent filter for HTTP requests

In the following exercise you register an activity as browser. This means, if an intent is triggered when someone wants to view an URL starting with http, your activity will be available to process this intent.

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

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

Register your activity to the Intent.Action_VIEW action and the scheme "http" via the following changes in your AndroidManifest.xml file Ensure that your 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 the corresponding layout file according the following listing.

<?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 {
  @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, the user should be able to select your custom browser implementation. You can, for example, trigger this intent via the application you created in Section 11, “Exercise: Using different implicit intents ”.

If you select your component, the HTML code is loaded and displayed into your TextView.

Tip

Replace your TextView with a WebView to create a "real" browser. The WebView does the loading of the HTTP request for you. Simply assign the URL via the loadUrl method to it.

13. Exercise: picking an image via an intent

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 { // 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.

14. Support free vogella tutorials

Maintaining high quality free online tutorials is a lot of work. Please support free tutorials by donating or by reporting typos and factual errors.

14.1. Thank you

Please consider a contribution if this article helped you.

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14.2. Questions and Discussion

If you find errors in this tutorial, please notify me (see the top of the page). Please note that due to the high volume of feedback I receive, I cannot answer questions to your implementation. Ensure you have read the vogella FAQ as I don't respond to questions already answered there.

15. Links and Literature

15.1. Source Code

Source Code of Examples

15.3. vogella Resources

vogella Training Android and Eclipse Training from the vogella team

Android Tutorial Introduction to Android Programming

GWT Tutorial Program in Java, compile to JavaScript and HTML

Eclipse RCP Tutorial Create native applications in Java

JUnit Tutorial Test your application

Git Tutorial Put all your files in a distributed version control system