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Android (Home screen) Widgets - Tutorial

Lars Vogel

Version 2.6

12.01.2013

Revision History
Revision 0.1 01.09.2010 Lars
Vogel
Created
Revision 0.2 - 2.6 13.12.2010 - 12.01.2013 Lars
Vogel
bug fixes and enhancements

Developing Android Widgets

This article describes how to create widgets in Android. It is based on Eclipse 4.2, Java 1.6 and Android 4.2.


Table of Contents

1. Prerequisites
2. Android Widgets
2.1. Overview about AppWidgets
2.2. Steps to create a Widget
2.3. Widget size
3. Creating the Broadcast receiver for the widget
3.1. Create and configure widget
3.2. Available views and layouts
3.3. AppWidgetProvider
4. Widget updates
5. Tutorial: Widget with fixed update interval
6. Collection View Widgets
7. Enabling a Widget for the Lock Screen
8. Tutorial: Update widget via a service
9. Support free vogella tutorials
9.1. Thank you
9.2. Questions and Discussion
10. Links and Literature
10.1. Source Code
10.2. Android Widget Resources
10.3. Android Resources
10.4. vogella Resources

1. Prerequisites

The following description assume that you have already experience in building standard Android application. Please see Android Tutorial. It also uses partly Android services. You find an introduction into Android Services in Android Service Tutorial.

2. Android Widgets

2.1. Overview about AppWidgets

Widgets are little applications which can be placed on a widget host, typically the home screen or the lockscreen, of your Android device.

A Widget runs as part of the process of its host. This requires that Widgets preserve the permissions of their application.

Widgets use RemoteViews to create there user interface. A RemoteView can be executed by another process with the same permissions as the original application. This way the Widget runs with the permissions of its defining application.

The user interface for a Widget is defined by an BroadcastReceiver. This BroadcastReceiver inflates its layout into an object of type RemoteViews. This RemoteViews object is delivered to Android, which hands it over the home screen application.

2.2. Steps to create a Widget

To create a Widgets you:

  • Define a layout file

  • Create an XML file (AppWidgetProviderInfo) which describes the properties of the widget, e.g. size or the fixed update frequency.

  • Create a BroadcastReceiver which is used to build the user interface of the Widget.

  • Enter the Widget configuration in the AndroidManifest.xml file.

  • Optional you can specify a configuration activity which is called once a new instance of the widget is added to the widget host.

2.3. Widget size

A Widget will take a certain amount of cells on the home screen. A cell is usually used to display the icon of one application. As a calculation rule you should define the size of the widget with the formula: ((Number of columns / rows)* 74) - 2. These are device independent pixels and the -2 is used to avoid rounding issues.

As of Android 3.1 a Widgets can be flexible in size, e.g. the user can make it larger or smaller. To enable this for Widgets you can use the android:resizeMode="horizontal|vertical" attribute in the XML configuration file for the widget.

3. Creating the Broadcast receiver for the widget

3.1. Create and configure widget

To register a widget you create a BroadcastReceiver with an intent filter for the android.appwidget.action.APPWIDGET_UPDATE action .

<receiver
       android:icon="@drawable/icon"
       android:label="Example Widget"
       android:name="MyWidgetProvider" >
       <intent-filter >
            <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
       </intent-filter>

       <meta-data
          android:name="android.appwidget.provider"
          android:resource="@xml/widget_info" />
</receiver> 

The BroadcastReceiver can get an label and icon assigned. These are used in the list of available Widgets.

You also specify the meta-data for the widget via the android:name="android.appwidget.provider attribute. The configuration file referred by this meta-data contains the configuration settings for the widget. If contains for example the update interface, the size and the initial layout of the widget.

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialLayout="@layout/widget_layout"
    android:minHeight="72dp"
    android:minWidth="146dp"
    android:updatePeriodMillis="1800000" >

</appwidget-provider> 

3.2. Available views and layouts

A widget is restricted in the View classes it can use. As layouts you can use the FrameLayout, LinearLayout and RelativeLayout classes. As views you can use AnalogClock, Button, Chromometer, ImageButton, ImageView, ProgressBar and TextView.

As of Android 3.0 more views are available: GridView, ListView, StackView, ViewFlipper and AdapterViewFlipper. This adapter Views require that you define a collection view widget which is described later in this book.

The only interaction that is possible on the Views of a Widget is via on OnClickListener. This OnClickListener can be registered on a widget and is triggered by the user.

3.3. AppWidgetProvider

Your BroadcastReceiver typically extends the AppWidgetProvider class.

The AppWidgetProvider class implements the onReceive() method, extracts the required information and calls the following widget lifecycle methods.

As you can add several instances of a widget to the home screen you have lifecycle methods which are called only for the first instance added / removed to the home screen and others which are called for every instance of your widget.

Table 1. Lifecycle method

Method Description
onEnabled() Called the first time an instance of your widget is added to the home screen
onDisabled() Called once the last instance of your widget is removed from the home screen.
onUpdate() Called for every update of the widget. Contains the ids of appWidgetIds for which an update is needed. Note that this may be all of the AppWidget instances for this provider, or just a subset of them, as stated in the methods JavaDoc. For example if more than one widget is added to the home screen, only the last one changes (until reinstall).
onDeleted() Widget instance is removed from the home screen

All long running operations in these methods should be performed in a service, as the execution time for a broadcast receiver is limited. Using asynchronous processing in the onReceive() method does not help as the system can kill the broadcast process after his onReceive() method.

4. Widget updates

A Widget gets its data on a periodic timetable. There are two methods to update a widget, one is based on an XML configuration file and the other is based on the Android AlarmManager service.

In the widget configuration file you can specify a fixed update interval. The system will wake up after this time interval and call your broadcast receiver to update the widget. The smallest update interval is 1800000 milliseconds (30 minutes).

The AlarmManager allows you to be more resource efficient and to have a higher frequency of updates. To use this approach you define a service and schedule this service via the AlarmManager regularly. This service updates the widget.

Please note that a higher update frequency will wake up the phone from the energy safe mode. As a result your widget consumes more energy.

5. Tutorial: Widget with fixed update interval

In the following tutorial you create a widget which displays a random number. This random number will updated automatically every 30 minutes. You also register a OnClickListener so that the widgets updates once the user clicks on it.

The resulting widget will look like the following.

Screenshot of the final Widget of this tutorial

Create a new Android project called de.vogella.android.widget.example with an activity in the package de.vogella.android.widget.example.

Create a new file myshape.xml in the /res/drawable directory. This file will define the background we use in your widget.

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <stroke
        android:width="2dp"
        android:color="#FFFFFFFF" />

    <gradient
        android:angle="225"
        android:endColor="#DD2ECCFA"
        android:startColor="#DD000000" />

    <corners
        android:bottomLeftRadius="7dp"
        android:bottomRightRadius="7dp"
        android:topLeftRadius="7dp"
        android:topRightRadius="7dp" />

</shape> 

Define the following widget_layout.xml file under the res/layout folder.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="8dip"
    android:background="@drawable/myshape" >

    <TextView
        android:id="@+id/update"
        style="@android:style/TextAppearance.Medium"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_gravity="center"
        android:gravity="center_horizontal|center_vertical"
        android:layout_margin="4dip"
        android:text="Static Text" >
    </TextView>

</LinearLayout> 

Create the AppWidgetProvider metadata widget_info.xml file, via FileNewAndroidAndroid XML File

Creating the widget provider 1

Creating the widget provider 2

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider 
      xmlns:android="http://schemas.android.com/apk/res/android"
    android:initialLayout="@layout/widget_layout"
    android:minHeight="72dp"
    android:minWidth="300dp"
    android:updatePeriodMillis="300000" >

</appwidget-provider> 

Create the following BroadcastReceiver which will be called for updates.

package de.vogella.android.widget.example;

import java.util.Random;

import android.app.PendingIntent;
import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import android.widget.RemoteViews;

public class MyWidgetProvider extends AppWidgetProvider {

  private static final String ACTION_CLICK = "ACTION_CLICK";

  @Override
  public void onUpdate(Context context, AppWidgetManager appWidgetManager,
      int[] appWidgetIds) {

    // Get all ids
    ComponentName thisWidget = new ComponentName(context,
        MyWidgetProvider.class);
    int[] allWidgetIds = appWidgetManager.getAppWidgetIds(thisWidget);
    for (int widgetId : allWidgetIds) {
      // create some random data
      int number = (new Random().nextInt(100));

      RemoteViews remoteViews = new RemoteViews(context.getPackageName(),
          R.layout.widget_layout);
      Log.w("WidgetExample", String.valueOf(number));
      // Set the text
      remoteViews.setTextViewText(R.id.update, String.valueOf(number));

      // Register an onClickListener
      Intent intent = new Intent(context, MyWidgetProvider.class);

      intent.setAction(AppWidgetManager.ACTION_APPWIDGET_UPDATE);
      intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS, appWidgetIds);

      PendingIntent pendingIntent = PendingIntent.getBroadcast(context,
          0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
      remoteViews.setOnClickPendingIntent(R.id.update, pendingIntent);
      appWidgetManager.updateAppWidget(widgetId, remoteViews);
    }
  }
} 

Open the AndroidManifest.xml and register your Widget.

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

    <application
        android:icon="@drawable/icon"
        android:label="@string/app_name" >
        <receiver android:name="MyWidgetProvider" >
            <intent-filter >
                <action 
                    android:name="android.appwidget.action.APPWIDGET_UPDATE" />
            </intent-filter>

            <meta-data
                android:name="android.appwidget.provider"
                android:resource="@xml/widget_info" />
        </receiver>
    </application>

    <uses-sdk android:minSdkVersion="8" />

</manifest> 

This attribute specifies that the AppWidgetProvider accepts the ACTION_APPWIDGET_UPDATE broadcast and specifies the metadata for the widget.

Run your app. Once your app has been deployed, long press on your desktop and install your new widget.

Installing the widget part 1

Installing the widget part 2

6. Collection View Widgets

Collection view Widgets add support for views like List, Stack and Grid.

For Collection view Widgets you need two layouts, one for the widget and one for each item in the widget collection.

The Widget items are filled by an instance of the RemoteViewsFactory factory class.

This factory class is provided by a service which must extend the RemoteViewsService class. This service requires the android.permission.BIND_REMOTEVIEWS permission.

To connect your Views with the service you use your onUpdate() method in your Widget receiver. You define an Intent pointing to the service and use the setRemoteAdapter method on the RemoteViews class.

Intent intent = new Intent(context, YourRemoteViewsService.class);
intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetId);
views.setRemoteAdapter(apppWidgetId,
  R.id.widget_your_id_to_collectionview,
  intent)
// Rest as normal 

7. Enabling a Widget for the Lock Screen

Since Android 4.2, it is possible to launch Home Screen application widgets on the Lock Screen of an Android device. For that you just need to additionally declare a widget to support “keyguard” category in the android:widgetCategory attribute in the AppWidgetProviderInfo XML file. The following code shows an example.

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
android:widgetCategory="keyguard|home_screen"
  ...
>
...
</appwidget-provider> 

In this example you declare a widget to support both - the Home and the Lock screens. If you recompile and launch your application now, you will be able to add the widget to the Lock Screen already.

You can also detect a widget category at runtime. For this in the AppWidgetProvider.onUpdate() method you can check for the category option of a widget with the following code.

Bundle options = appWidgetManager.getAppWidgetOptions(widgetId);

int category = options.getInt(AppWidgetManager.OPTION_APPWIDGET_HOST_CATEGORY, -1);
boolean isLockScreen = category == AppWidgetProviderInfo.WIDGET_CATEGORY_KEYGUARD; 

Using this technique you can decide in runtime whether widgets, your application provides, will look different, when they are hosted on the Lock Screen.

Similarly to how you used android:initialLayout attribute for defining an initial layout for Home screen widgets, you can use a new android:initialKeyguardLayout attribute for Lock screen in the AppWidgetProviderInfo XML file. This layout will appear immediately after a widget is added and will be replaced by the real layout once widget is initialized.

8. Tutorial: Update widget via a service

A BroadcastReceiver must finish his onReceive() method within 5 secs.

For potentially long running actions, as for example network access, you should do this processing in a service and perform the update the widgets from the service.

The following will demonstrate the usage of a service to update the widget.

Create the following UpdateWidgetService class in your project.

package de.vogella.android.widget.example;

import java.util.Random;

import android.app.PendingIntent;
import android.app.Service;
import android.appwidget.AppWidgetManager;
import android.content.ComponentName;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;
import android.widget.RemoteViews;

public class UpdateWidgetService extends Service {
  private static final String LOG = "de.vogella.android.widget.example";

  @Override
  public void onStart(Intent intent, int startId) {
    Log.i(LOG, "Called");
    // create some random data

    AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(this
        .getApplicationContext());

    int[] allWidgetIds = intent
        .getIntArrayExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS);

    ComponentName thisWidget = new ComponentName(getApplicationContext(),
        MyWidgetProvider.class);
    int[] allWidgetIds2 = appWidgetManager.getAppWidgetIds(thisWidget);
    Log.w(LOG, "From Intent" + String.valueOf(allWidgetIds.length));
    Log.w(LOG, "Direct" + String.valueOf(allWidgetIds2.length));

    for (int widgetId : allWidgetIds) {
      // create some random data
      int number = (new Random().nextInt(100));

      RemoteViews remoteViews = new RemoteViews(this
          .getApplicationContext().getPackageName(),
          R.layout.widget_layout);
      Log.w("WidgetExample", String.valueOf(number));
      // Set the text
      remoteViews.setTextViewText(R.id.update,
          "Random: " + String.valueOf(number));

      // Register an onClickListener
      Intent clickIntent = new Intent(this.getApplicationContext(),
          MyWidgetProvider.class);

      clickIntent.setAction(AppWidgetManager.ACTION_APPWIDGET_UPDATE);
      clickIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS,
          allWidgetIds);

      PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 0, clickIntent,
          PendingIntent.FLAG_UPDATE_CURRENT);
      remoteViews.setOnClickPendingIntent(R.id.update, pendingIntent);
      appWidgetManager.updateAppWidget(widgetId, remoteViews);
    }
    stopSelf();

    super.onStart(intent, startId);
  }

  @Override
  public IBinder onBind(Intent intent) {
    return null;
  }
} 

Add this class as a Service to your AndroidManifest.xml file.

<service android:name=".UpdateWidgetService"></service> 

Change MyWidgetProvider to the following. It will now only construct the service and start it.

package de.vogella.android.widget.example;

import android.appwidget.AppWidgetManager;
import android.appwidget.AppWidgetProvider;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

public class MyWidgetProvider extends AppWidgetProvider {

  private static final String LOG = "de.vogella.android.widget.example";

  @Override
  public void onUpdate(Context context, AppWidgetManager appWidgetManager,
      int[] appWidgetIds) {

    Log.w(LOG, "onUpdate method called");
    // Get all ids
    ComponentName thisWidget = new ComponentName(context,
        MyWidgetProvider.class);
    int[] allWidgetIds = appWidgetManager.getAppWidgetIds(thisWidget);

    // Build the intent to call the service
    Intent intent = new Intent(context.getApplicationContext(),
        UpdateWidgetService.class);
    intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS, allWidgetIds);

    // Update the widgets via the service
    context.startService(intent);
  }
} 

Once called this service will update all widgets. You can click on one of the widgets to update all widgets.

9. 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.

9.1. Thank you

Please consider a contribution if this article helped you.

Flattr this

9.2. 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.

10. Links and Literature

10.1. Source Code

Source Code of Examples

10.2. Android Widget Resources

Example Widget from Android API demos

Wiktionary Example Widget

http://code.google.com/p/wiktionary-android/source/browse/trunk/Wiktionary/src/com/example/android/wiktionary/

10.4. 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