- Home Startseite ホーム 主页 首頁
- SDK
- Dev Guide Handbuch Guía Guide Guida 開発ガイド 开发人员指南 開發指南
- Reference Referenz Referencia Référence Riferimento リファレンス 参考 參考資料
- Resources
- Videos ビデオ
- Blog ブログ 博客 網誌

Android.com

# App Widgets

## Quickview

- App Widgets provide users access to some of your application features directly from the Home screen (without the need to launch an activity)
- App Widgets are backed by a special kind of broadcast receiver that handles the App Widget lifecycle

## In this document

1. The Basics
2. Declaring an App Widget in the Manifest
3. Adding the AppWidgetProviderInfo Metadata
4. Creating the App Widget Layout
5. Using the AppWidgetProvider Class
   1. Receiving App Widget broadcast Intents
6. Creating an App Widget Configuration Activity
   1. Updating the App Widget from the configuration Activity
7. Setting a Preview Image
8. Using App Widgets with Collections
   1. Sample application
   2. Implementing app widgets with collections
   3. Keeping Collection Data Fresh

## Key classes

1. `AppWidgetProvider`
2. `AppWidgetProviderInfo`
3. `AppWidgetManager`

## See also

1. App Widget Design Guidelines
2. Introducing home screen widgets and the AppWidget framework »

App Widgets are miniature application views that can be embedded in other applications (such as the Home screen) and receive periodic updates. These views are referred to as Widgets in the user interface, and you can publish one with an App Widget provider. An application component that is able to hold other App Widgets is called an App Widget host. The screenshot below shows the Music App Widget.

This document describes how to publish an App Widget using an App Widget provider.

## The Basics

To create an App Widget, you need the following:

`AppWidgetProviderInfo` object
  Describes the metadata for an App Widget, such as the App Widget's layout, update frequency, and the AppWidgetProvider class. This should be defined in XML.
`AppWidgetProvider` class implementation
  Defines the basic methods that allow you to programmatically interface with the App Widget, based on broadcast events. Through it, you will receive broadcasts when the App Widget is updated, enabled, disabled and deleted.
View layout
  Defines the initial layout for the App Widget, defined in XML.

Additionally, you can implement an App Widget configuration Activity. This is an optional `Activity` that launches when the user adds your App Widget and allows him or her to modify App Widget settings at create-time.

The following sections describe how to setup each of these components.

## Declaring an App Widget in the Manifest

First, declare the `AppWidgetProvider` class in your application's `AndroidManifest.xml` file. For example:

    <receiver android:name="ExampleAppWidgetProvider" >
        <intent-filter>
            <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
        </intent-filter>
        <meta-data android:name="android.appwidget.provider"
                   android:resource="@xml/example_appwidget_info" />
    </receiver>

The `<receiver>` element requires the `android:name` attribute, which specifies the `AppWidgetProvider` used by the App Widget.

The `<intent-filter>` element must include an `<action>` element with the `android:name` attribute. This attribute specifies that the `AppWidgetProvider` accepts the `ACTION_APPWIDGET_UPDATE` broadcast. This is the only broadcast that you must explicitly declare. The `AppWidgetManager` automatically sends all other App Widget broadcasts to the AppWidgetProvider as necessary.

The `<meta-data>` element specifies the `AppWidgetProviderInfo` resource and requires the following attributes:

- `android:name` - Specifies the metadata name. Use `android.appwidget.provider` to identify the data as the `AppWidgetProviderInfo` descriptor.
- `android:resource` - Specifies the `AppWidgetProviderInfo` resource location.

## Adding the AppWidgetProviderInfo Metadata

The `AppWidgetProviderInfo` defines the essential qualities of an App Widget, such as its minimum layout dimensions, its initial layout resource, how often to update the App Widget, and (optionally) a configuration Activity to launch at create-time. Define the AppWidgetProviderInfo object in an XML resource using a single `<appwidget-provider>` element and save it in the project's `res/xml/` folder.

For example:

    <appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
        android:minWidth="294dp"
        android:minHeight="72dp"
        android:updatePeriodMillis="86400000"
        android:previewImage="@drawable/preview"
        android:initialLayout="@layout/example_appwidget"
        android:configure="com.example.android.ExampleAppWidgetConfigure"
        android:resizeMode="horizontal|vertical">
    </appwidget-provider>

Here's a summary of the `<appwidget-provider>` attributes:

- The values for the `minWidth` and `minHeight` attributes specify the minimum area required by the App Widget's layout.

  The default Home screen positions App Widgets in its window based on a grid of cells that have a defined height and width. If the values for an App Widget's minimum width or height don't match the dimensions of the cells, then the App Widget dimensions round up to the nearest cell size. (See the App Widget Design Guidelines for more information on the Home screen cell sizes.)

  Because the Home screen's layout orientation (and thus, the cell sizes) can change, as a rule of thumb, you should assume the worst-case cell size of 74 pixels for the height and width of a cell. However, you must subtract 2 from the final dimension to account for any integer rounding errors that occur in the pixel count. To find your minimum width and height in density-independent pixels (dp), use this formula:
  `(number of cells * 74) - 2`
  Following this formula, you should use 72 dp for a height of one cell, 294 dp and for a width of four cells.

  Note: To make your app widget portable across devices, your app widget's minimum size should never be larger than 4 x 4 cells. See the App Widget Design Guidelines for more discussion of Home screen cell sizes.

- The `updatePeriodMillis` attribute defines how often the App Widget framework should request an update from the `AppWidgetProvider` by calling the `onUpdate()` callback method. The actual update is not guaranteed to occur exactly on time with this value and we suggest updating as infrequently as possible—perhaps no more than once an hour to conserve the battery. You might also allow the user to adjust the frequency in a configuration—some people might want a stock ticker to update every 15 minutes, or maybe only four times a day.

  Note: If the device is asleep when it is time for an update (as defined by `updatePeriodMillis`), then the device will wake up in order to perform the update. If you don't update more than once per hour, this probably won't cause significant problems for the battery life. If, however, you need to update more frequently and/or you do not need to update while the device is asleep, then you can instead perform updates based on an alarm that will not wake the device. To do so, set an alarm with an Intent that your AppWidgetProvider receives, using the `AlarmManager`. Set the alarm type to either `ELAPSED_REALTIME` or `RTC`, which will only deliver the alarm when the device is awake. Then set `updatePeriodMillis` to zero (`"0"`).

- The `initialLayout` attribute points to the layout resource that defines the App Widget layout.
- The `configure` attribute defines the `Activity` to launch when the user adds the App Widget, in order for him or her to configure App Widget properties. This is optional (read Creating an App Widget Configuration Activity below).
- The `previewImage` attribute specifies a preview of what the app widget will look like after it's configured, which the user sees when selecting the app widget. If not supplied, the user instead sees your application's launcher icon. This field corresponds to the `android:previewImage` attribute in the `<receiver>` element in the `AndroidManifest.xml` file. For more discussion of using `previewImage`, see Setting a Preview Image. Introduced in Android 3.0.
- The `autoAdvanceViewId` attribute specifies the view ID of the app widget subview that should be auto-advanced by the widget's host. Introduced in Android 3.0.
- The `resizeMode` attribute specifies the rules by which a widget can be resized. You use this attribute to make homescreen widgets resizeable—horizontally, vertically, or on both axes. Users touch-hold a widget to show its resize handles, then drag the horizontal and/or vertical handles to change the size on the layout grid. Values for the `resizeMode` attribute include "horizontal", "vertical", and "none". To declare a widget as resizeable horizontally and vertically, supply the value "horizontal|vertical". Introduced in Android 3.1.

See the `AppWidgetProviderInfo` class for more information on the attributes accepted by the `<appwidget-provider>` element.

## Creating the App Widget Layout

You must define an initial layout for your App Widget in XML and save it in the project's `res/layout/` directory. You can design your App Widget using the View objects listed below, but before you begin designing your App Widget, please read and understand the App Widget Design Guidelines.

Creating the App Widget layout is simple if you're familiar with XML Layouts. However, you must be aware that App Widget layouts are based on `RemoteViews`, which do not support every kind of layout or view widget.

A RemoteViews object (and, consequently, an App Widget) can support the following layout classes:

- `FrameLayout`
- `LinearLayout`
- `RelativeLayout`

And the following widget classes:

- `AnalogClock`
- `Button`
- `Chronometer`
- `ImageButton`
- `ImageView`
- `ProgressBar`
- `TextView`
- `ViewFlipper`

Descendants of these classes are not supported.

### Adding margins to App Widgets

Widgets should not generally extend to screen edges and should not visually be flush with other widgets, so you should add margins on all sides around your widget frame.

As of Android 4.0, app widgets are automatically given padding between the widget frame and the app widget's bounding box to provide better alignment with other widgets and icons on the user's home screen. To take advantage of this strongly recommended behavior, set your application's targetSdkVersion to 14 or greater.

It's easy to write a single layout that has custom margins applied for earlier versions of the platform, and has no extra margins for Android 4.0 and greater:

1. Set your application's `targetSdkVersion` to 14 or greater.
2. Create a layout such as the one below, that references a dimension resource for its margins:

       <FrameLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:layout_margin="@dimen/widget_margin">

         <LinearLayout
           android:layout_width="match_parent"
           android:layout_height="match_parent"
           android:orientation="horizontal"
           android:background="@drawable/my_widget_background">
           …
         </LinearLayout>

       </FrameLayout>

3. Create two dimensions resources, one in `res/values/` to provide the pre-Android 4.0 custom margins, and one in `res/values-v14/` to provide no extra padding for Android 4.0 widgets:

   res/values/dimens.xml:

       <dimen name="widget_margin">15dp</dimen>

   res/values-v14/dimens.xml:

       <dimen name="widget_margin">0dp</dimen>

Another option is to simply build extra margins into your nine-patch background assets by default, and provide different nine-patches with no margins for API level 14 or later.

## Using the AppWidgetProvider Class

You must declare your AppWidgetProvider class implementation as a broadcast receiver using the `<receiver>` element in the AndroidManifest (see Declaring an App Widget in the Manifest above).

The `AppWidgetProvider` class extends BroadcastReceiver as a convenience class to handle the App Widget broadcasts. The AppWidgetProvider receives only the event broadcasts that are relevant to the App Widget, such as when the App Widget is updated, deleted, enabled, and disabled. When these broadcast events occur, the AppWidgetProvider receives the following method calls:

`onUpdate()`
  This is called to update the App Widget at intervals defined by the `updatePeriodMillis` attribute in the AppWidgetProviderInfo (see Adding the AppWidgetProviderInfo Metadata above). This method is also called when the user adds the App Widget, so it should perform the essential setup, such as define event handlers for Views and start a temporary `Service`, if necessary. However, if you have declared a configuration Activity, this method is not called when the user adds the App Widget, but is called for the subsequent updates. It is the responsibility of the configuration Activity to perform the first update when configuration is done. (See Creating an App Widget Configuration Activity below.)
`onDeleted(Context, int[])`
  This is called every time an App Widget is deleted from the App Widget host.
`onEnabled(Context)`
  This is called when an instance the App Widget is created for the first time. For example, if the user adds two instances of your App Widget, this is only called the first time. If you need to open a new database or perform other setup that only needs to occur once for all App Widget instances, then this is a good place to do it.
`onDisabled(Context)`
  This is called when the last instance of your App Widget is deleted from the App Widget host. This is where you should clean up any work done in `onEnabled(Context)`, such as delete a temporary database.
`onReceive(Context, Intent)`
  This is called for every broadcast and before each of the above callback methods. You normally don't need to implement this method because the default AppWidgetProvider implementation filters all App Widget broadcasts and calls the above methods as appropriate.

Note: In Android 1.5, there is a known issue in which the `onDeleted()` method will not be called when it should be. To work around this issue, you can implement `onReceive()` as described in this Group post to receive the `onDeleted()` callback.

The most important AppWidgetProvider callback is `onUpdate()` because it is called when each App Widget is added to a host (unless you use a configuration Activity). If your App Widget accepts any user interaction events, then you need to register the event handlers in this callback. If your App Widget doesn't create temporary files or databases, or perform other work that requires clean-up, then `onUpdate()` may be the only callback method you need to define. For example, if you want an App Widget with a button that launches an Activity when clicked, you could use the following implementation of AppWidgetProvider:

    public class ExampleAppWidgetProvider extends AppWidgetProvider {

        public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
            final int N = appWidgetIds.length;

            // Perform this loop procedure for each App Widget that belongs to this provider
            for (int i=0; i<N; i++) {
                int appWidgetId = appWidgetIds[i];

                // Create an Intent to launch ExampleActivity
                Intent intent = new Intent(context, ExampleActivity.class);
                PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, 0);

                // Get the layout for the App Widget and attach an on-click listener
                // to the button
                RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.appwidget_provider_layout);
                views.setOnClickPendingIntent(R.id.button, pendingIntent);

                // Tell the AppWidgetManager to perform an update on the current app widget
                appWidgetManager.updateAppWidget(appWidgetId, views);
            }
        }
    }

This AppWidgetProvider defines only the `onUpdate()` method for the purpose of defining a `PendingIntent` that launches an `Activity` and attaching it to the App Widget's button with `setOnClickPendingIntent(int, PendingIntent)`. Notice that it includes a loop that iterates through each entry in `appWidgetIds`, which is an array of IDs that identify each App Widget created by this provider. In this way, if the user creates more than one instance of the App Widget, then they are all updated simultaneously. However, only one `updatePeriodMillis` schedule will be managed for all instances of the App Widget. For example, if the update schedule is defined to be every two hours, and a second instance of the App Widget is added one hour after the first one, then they will both be updated on the period defined by the first one and the second update period will be ignored (they'll both be updated every two hours, not every hour).

Note: Because `AppWidgetProvider` is an extension of `BroadcastReceiver`, your process is not guaranteed to keep running after the callback methods return (see `BroadcastReceiver` for information about the broadcast lifecycle). If your App Widget setup process can take several seconds (perhaps while performing web requests) and you require that your process continues, consider starting a `Service` in the `onUpdate()` method. From within the Service, you can perform your own updates to the App Widget without worrying about the AppWidgetProvider closing down due to an Application Not Responding (ANR) error. See the Wiktionary sample's AppWidgetProvider for an example of an App Widget running a `Service`.

Also see the ExampleAppWidgetProvider.java sample class.

### Receiving App Widget broadcast Intents

`AppWidgetProvider` is just a convenience class. If you would like to receive the App Widget broadcasts directly, you can implement your own `BroadcastReceiver` or override the `onReceive(Context, Intent)` callback. The four Intents you need to care about are:

- `ACTION_APPWIDGET_UPDATE`
- `ACTION_APPWIDGET_DELETED`
- `ACTION_APPWIDGET_ENABLED`
- `ACTION_APPWIDGET_DISABLED`

## Creating an App Widget Configuration Activity

If you would like the user to configure settings when he or she adds a new App Widget, you can create an App Widget configuration Activity. This `Activity` will be automatically launched by the App Widget host and allows the user to configure available settings for the App Widget at create-time, such as the App Widget color, size, update period or other functionality settings.

The configuration Activity should be declared as a normal Activity in the Android manifest file. However, it will be launched by the App Widget host with the `ACTION_APPWIDGET_CONFIGURE` action, so the Activity needs to accept this Intent. For example:

    <activity android:name=".ExampleAppWidgetConfigure">
        <intent-filter>
            <action android:name="android.appwidget.action.APPWIDGET_CONFIGURE"/>
        </intent-filter>
    </activity>

Also, the Activity must be declared in the AppWidgetProviderInfo XML file, with the `android:configure` attribute (see Adding the AppWidgetProviderInfo Metadata above). For example, the configuration Activity can be declared like this:

    <appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
        ...
        android:configure="com.example.android.ExampleAppWidgetConfigure"
        ... >
    </appwidget-provider>

Notice that the Activity is declared with a fully-qualified namespace, because it will be referenced from outside your package scope.

That's all you need to get started with a configuration Activity. Now all you need is the actual Activity. There are, however, two important things to remember when you implement the Activity:

- The App Widget host calls the configuration Activity and the configuration Activity should always return a result. The result should include the App Widget ID passed by the Intent that launched the Activity (saved in the Intent extras as `EXTRA_APPWIDGET_ID`).
- The `onUpdate()` method will not be called when the App Widget is created (the system will not send the ACTION_APPWIDGET_UPDATE broadcast when a configuration Activity is launched). It is the responsibility of the configuration Activity to request an update from the AppWidgetManager when the App Widget is first created. However, `onUpdate()` will be called for subsequent updates—it is only skipped the first time.

See the code snippets in the following section for an example of how to return a result from the configuration and update the App Widget.

### Updating the App Widget from the configuration Activity

When an App Widget uses a configuration Activity, it is the responsibility of the Activity to update the App Widget when configuration is complete. You can do so by requesting an update directly from the `AppWidgetManager`.

Here's a summary of the procedure to properly update the App Widget and close the configuration Activity:

1. First, get the App Widget ID from the Intent that launched the Activity:

       Intent intent = getIntent();
       Bundle extras = intent.getExtras();
       if (extras != null) {
           mAppWidgetId = extras.getInt(
                   AppWidgetManager.EXTRA_APPWIDGET_ID,
                   AppWidgetManager.INVALID_APPWIDGET_ID);
       }

2. Perform your App Widget configuration.
3. When the configuration is complete, get an instance of the AppWidgetManager by calling `getInstance(Context)`:

       AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);

4. Update the App Widget with a `RemoteViews` layout by calling `updateAppWidget(int, RemoteViews)`:

       RemoteViews views = new RemoteViews(context.getPackageName(),
       R.layout.example_appwidget);
       appWidgetManager.updateAppWidget(mAppWidgetId, views);

5. Finally, create the return Intent, set it with the Activity result, and finish the Activity:

    Intent resultValue = new Intent();
    resultValue.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, mAppWidgetId);
    setResult(RESULT_OK, resultValue);
    finish();

Tip: When your configuration Activity first opens, set the Activity result to RESULT_CANCELED. This way, if the user backs-out of the Activity before reaching the end, the App Widget host is notified that the configuration was cancelled and the App Widget will not be added.

See the ExampleAppWidgetConfigure.java sample class in ApiDemos for an example.

## Setting a Preview Image

Android 3.0 introduces the `previewImage` field, which specifies a preview of what the app widget looks like. This preview is shown to the user from the widget picker. If this field is not supplied, the app widget's icon is used for the preview.

This is how you specify this setting in XML:

    <appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
      ...
      android:previewImage="@drawable/preview">
    </appwidget-provider>

To help create a preview image for your app widget (to specify in the `previewImage` field), the Android emulator includes an application called "Widget Preview." To create a preview image, launch this application, select the app widget for your application and set it up how you'd like your preview image to appear, then save it and place it in your application's drawable resources.

## Using App Widgets with Collections

Android 3.0 introduces App Widgets with collections. These kinds of App Widgets use the `RemoteViewsService` to display collections that are backed by remote data, such as from a content provider. The data provided by the `RemoteViewsService` is presented in the App Widget using one of the following view types, which we’ll refer to as “collection views:”

`ListView`
  A view that shows items in a vertically scrolling list. For an example, see the Gmail app widget.
`GridView`
  A view that shows items in two-dimensional scrolling grid. For an example, see the Bookmarks app widget.
`StackView`
  A stacked card view (kind of like a rolodex), where the user can flick the front card up/down to see the previous/next card, respectively. Examples include the YouTube and Books app widgets.
`AdapterViewFlipper`
  An adapter-backed simple `ViewAnimator` that animates between two or more views. Only one child is shown at a time.

As stated above, these collection views display collections backed by remote data. This means that they use an `Adapter` to bind their user interface to their data. An `Adapter` binds individual items from a set of data into individual `View` objects. Because these collection views are backed by adapters, the Android framework must include extra architecture to support their use in app widgets. In the context of an app widget, the `Adapter` is replaced by a `RemoteViewsFactory`, which is simply a thin wrapper around the `Adapter` interface. When requested for a specific item in the collection, the `RemoteViewsFactory` creates and returns the item for the collection as a `RemoteViews` object. In order to include a collection view in your app widget, you must implement `RemoteViewsService` and `RemoteViewsFactory`.

`RemoteViewsService` is a service that allows a remote adapter to request `RemoteViews` objects. `RemoteViewsFactory` is an interface for an adapter between a collection view (such as `ListView`, `GridView`, and so on) and the underlying data for that view. From the StackView Widget sample, here is an example of the boilerplate code you use to implement this service and interface:

    public class StackWidgetService extends RemoteViewsService {
        @Override
        public RemoteViewsFactory onGetViewFactory(Intent intent) {
            return new StackRemoteViewsFactory(this.getApplicationContext(), intent);
        }
    }

    class StackRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory {

    //... include adapter-like methods here. See the StackView Widget sample.

    }

### Sample application

The code excerpts in this section are drawn from the StackView Widget sample:

This sample consists of a stack of 10 views, which display the values `"0!"` through `"9!"` The sample app widget has these primary behaviors:

- The user can vertically fling the top view in the app widget to display the next or previous view. This is a built-in StackView behavior.
- Without any user interaction, the app widget automatically advances through its views in sequence, like a slide show. This is due to the setting `android:autoAdvanceViewId="@id/stack_view"` in the `res/xml/stackwidgetinfo.xml` file. This setting applies to the view ID, which in this case is the view ID of the stack view.
- If the user touches the top view, the app widget displays the `Toast` message "Touched view n," where n is the index (position) of the touched view. For more discussion of how this is implemented, see Adding behavior to individual items.

### Implementing app widgets with collections

To implement an App Widget with collections, you follow the same basic steps you would use to implement any app widget. The following sections describe the additional steps you need to perform to implement an App Widget with collections.

#### Manifest for app widgets with collections

In addition to the requirements listed in Declaring an App Widget in the Manifest, to make it possible for App Widgets with collections to bind to your `RemoteViewsService`, you must declare the service in your manifest file with the permission `BIND_REMOTEVIEWS`. This prevents other applications from freely accessing your app widget's data. For example, when creating an App Widget that uses `RemoteViewsService` to populate a collection view, the manifest entry may look like this:

    <service android:name="MyWidgetService"
    ...
    android:permission="android.permission.BIND_REMOTEVIEWS" />

The line `android:name="MyWidgetService"` refers to your subclass of `RemoteViewsService`.

#### Layout for app widgets with collections

The main requirement for your app widget layout XML file is that it include one of the collection views: `ListView`, `GridView`, `StackView`, or `AdapterViewFlipper`. Here is the `widget_layout.xml` for the StackView Widget sample:

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

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <StackView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/stack_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:loopViews="true" />
        <TextView xmlns:android="http://schemas.android.com/apk/res/android"
            android:id="@+id/empty_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:gravity="center"
            android:background="@drawable/widget_item_background"
            android:textColor="#ffffff"
            android:textStyle="bold"
            android:text="@string/empty_view_text"
            android:textSize="20sp" />
    </FrameLayout>

Note that empty views must be siblings of the collection view for which the empty view represents empty state.

In addition to the layout file for your entire app widget, you must create another layout file that defines the layout for each item in the collection (for example, a layout for each book in a collection of books). For example, the StackView Widget sample only has one layout file, `widget_item.xml`, since all items use the same layout. But the WeatherListWidget sample has two layout files: `dark_widget_item.xml` and `light_widget_item.xml`.

#### AppWidgetProvider class for app widgets with collections

As with a regular app widget, the bulk of your code in your `AppWidgetProvider` subclass typically goes in `onUpdate()`. The major difference in your implementation for `onUpdate()` when creating an app widget with collections is that you must call `setRemoteAdapter()`. This tells the collection view where to get its data. The `RemoteViewsService` can then return your implementation of `RemoteViewsFactory`, and the widget can serve up the appropriate data. When you call this method, you must pass an intent that points to your implementation of `RemoteViewsService` and the App Widget ID that specifies the app widget to update.

For example, here's how the StackView Widget sample implements the `onUpdate()` callback method to set the `RemoteViewsService` as the remote adapter for the app widget collection:

    public void onUpdate(Context context, AppWidgetManager appWidgetManager,
    int[] appWidgetIds) {
        // update each of the app widgets with the remote adapter
        for (int i = 0; i < appWidgetIds.length; ++i) {

            // Set up the intent that starts the StackViewService, which will
            // provide the views for this collection.
            Intent intent = new Intent(context, StackWidgetService.class);
            // Add the app widget ID to the intent extras.
            intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[i]);
            intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME)));
            // Instantiate the RemoteViews object for the App Widget layout.
            RemoteViews rv = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
            // Set up the RemoteViews object to use a RemoteViews adapter.
            // This adapter connects
            // to a RemoteViewsService  through the specified intent.
            // This is how you populate the data.
            rv.setRemoteAdapter(appWidgetIds[i], R.id.stack_view, intent);

            // The empty view is displayed when the collection has no items.
            // It should be in the same layout used to instantiate the RemoteViews
            // object above.
            rv.setEmptyView(R.id.stack_view, R.id.empty_view);

            //
            // Do additional processing specific to this app widget...
            //

            appWidgetManager.updateAppWidget(appWidgetIds[i], rv);
        }
        super.onUpdate(context, appWidgetManager, appWidgetIds);
    }

#### RemoteViewsService class

### Persisting data

You can’t rely on a single instance of your service, or any data it contains, to persist. You should therefore not store any data in your `RemoteViewsService` (unless it is static). If you want your app widget’s data to persist, the best approach is to use a `ContentProvider` whose data persists beyond the process lifecycle.

As described above, your `RemoteViewsService` subclass provides the `RemoteViewsFactory` used to populate the remote collection view.

Specifically, you need to perform these steps:

1. Subclass `RemoteViewsService`. `RemoteViewsService` is the service through which a remote adapter can request `RemoteViews`.
2. In your `RemoteViewsService` subclass, include a class that implements the `RemoteViewsFactory` interface. `RemoteViewsFactory` is an interface for an adapter between a remote collection view (such as `ListView`, `GridView`, and so on) and the underlying data for that view. Your implementation is responsible for making a `RemoteViews` object for each item in the data set. This interface is a thin wrapper around `Adapter`.

The primary contents of the `RemoteViewsService` implementation is its `RemoteViewsFactory`, described below.

#### RemoteViewsFactory interface

Your custom class that implements the `RemoteViewsFactory` interface provides the app widget with the data for the items in its collection. To do this, it combines your app widget item XML layout file with a source of data. This source of data could be anything from a database to a simple array. In the StackView Widget sample, the data source is an array of `WidgetItems`. The `RemoteViewsFactory` functions as an adapter to glue the data to the remote collection view.

The two most important methods you need to implement for your `RemoteViewsFactory` subclass are `onCreate()` and `getViewAt()` .

The system calls `onCreate()` when creating your factory for the first time. This is where you set up any connections and/or cursors to your data source. For example, the StackView Widget sample uses `onCreate()` to initialize an array of `WidgetItem` objects. When your app widget is active, the system accesses these objects using their index position in the array and the text they contain is displayed

Here is an excerpt from the the StackView Widget sample's `RemoteViewsFactory` implementation that shows portions of the `onCreate()` method:

    class StackRemoteViewsFactory implements
    RemoteViewsService.RemoteViewsFactory {
        private static final int mCount = 10;
        private List<WidgetItem> mWidgetItems = new ArrayList<WidgetItem>();
        private Context mContext;
        private int mAppWidgetId;

        public StackRemoteViewsFactory(Context context, Intent intent) {
            mContext = context;
            mAppWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                    AppWidgetManager.INVALID_APPWIDGET_ID);
        }

        public void onCreate() {
            // In onCreate() you setup any connections / cursors to your data source. Heavy lifting,
            // for example downloading or creating content etc, should be deferred to onDataSetChanged()
            // or getViewAt(). Taking more than 20 seconds in this call will result in an ANR.
            for (int i = 0; i < mCount; i++) {
                mWidgetItems.add(new WidgetItem(i + "!"));
            }
            ...
        }
    ...

The `RemoteViewsFactory` method `getViewAt()` returns a `RemoteViews` object corresponding to the data at the specified `position` in the data set. Here is an excerpt from the StackView Widget sample's `RemoteViewsFactory` implementation:

    public RemoteViews getViewAt(int position) {

        // Construct a remote views item based on the app widget item XML file,
        // and set the text based on the position.
        RemoteViews rv = new RemoteViews(mContext.getPackageName(), R.layout.widget_item);
        rv.setTextViewText(R.id.widget_item, mWidgetItems.get(position).text);

        ...
        // Return the remote views object.
        return rv;
    }

#### Adding behavior to individual items

The above sections show you how to bind your data to your app widget collection. But what if you want to add dynamic behavior to the individual items in your collection view?

As described in Using the AppWidgetProvider Class, you normally use `setOnClickPendingIntent()` to set an object's click behavior—such as to cause a button to launch an `Activity`. But this approach is not allowed for child views in an individual collection item (to clarify, you could use `setOnClickPendingIntent()` to set up a global button in the Gmail app widget that launches the app, for example, but not on the individual list items). Instead, to add click behavior to individual items in a collection, you use `setOnClickFillInIntent()`. This entails setting up up a pending intent template for your collection view, and then setting a fill-in intent on each item in the collection via your `RemoteViewsFactory`.

This section uses the StackView Widget sample to describe how to add behavior to individual items. In the StackView Widget sample, if the user touches the top view, the app widget displays the `Toast` message "Touched view n," where n is the index (position) of the touched view. This is how it works:

- The `StackWidgetProvider` (an `AppWidgetProvider` subclass) creates a pending intent that has a custom action called `TOAST_ACTION`.
- When the user touches a view, the intent is fired and it broadcasts `TOAST_ACTION`.
- This broadcast is intercepted by the `StackWidgetProvider`'s `onReceive()` method, and the app widget displays the `Toast` message for the touched view. The data for the collection items is provided by the `RemoteViewsFactory`, via the `RemoteViewsService`.

Note: The StackView Widget sample uses a broadcast, but typically an app widget would simply launch an activity in a scenario like this one.

##### Setting up the pending intent template

The `StackWidgetProvider` (`AppWidgetProvider` subclass) sets up a pending intent. Individuals items of a collection cannot set up their own pending intents. Instead, the collection as a whole sets up a pending intent template, and the individual items set a fill-in intent to create unique behavior on an item-by-item basis.

This class also receives the broadcast that is sent when the user touches a view. It processes this event in its `onReceive()` method. If the intent's action is `TOAST_ACTION`, the app widget displays a `Toast` message for the current view.

    public class StackWidgetProvider extends AppWidgetProvider {
        public static final String TOAST_ACTION = "com.example.android.stackwidget.TOAST_ACTION";
        public static final String EXTRA_ITEM = "com.example.android.stackwidget.EXTRA_ITEM";

        ...

        // Called when the BroadcastReceiver receives an Intent broadcast.
        // Checks to see whether the intent's action is TOAST_ACTION. If it is, the app widget
        // displays a Toast message for the current item.
        @Override
        public void onReceive(Context context, Intent intent) {
            AppWidgetManager mgr = AppWidgetManager.getInstance(context);
            if (intent.getAction().equals(TOAST_ACTION)) {
                int appWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                    AppWidgetManager.INVALID_APPWIDGET_ID);
                int viewIndex = intent.getIntExtra(EXTRA_ITEM, 0);
                Toast.makeText(context, "Touched view " + viewIndex, Toast.LENGTH_SHORT).show();
            }
            super.onReceive(context, intent);
        }

        @Override
        public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
            // update each of the app widgets with the remote adapter
            for (int i = 0; i < appWidgetIds.length; ++i) {

                // Sets up the intent that points to the StackViewService that will
                // provide the views for this collection.
                Intent intent = new Intent(context, StackWidgetService.class);
                intent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[i]);
                // When intents are compared, the extras are ignored, so we need to embed the extras
                // into the data so that the extras will not be ignored.
                intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME)));
                RemoteViews rv = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
                rv.setRemoteAdapter(appWidgetIds[i], R.id.stack_view, intent);

                // The empty view is displayed when the collection has no items. It should be a sibling
                // of the collection view.
                rv.setEmptyView(R.id.stack_view, R.id.empty_view);

                // This section makes it possible for items to have individualized behavior.
                // It does this by setting up a pending intent template. Individuals items of a collection
                // cannot set up their own pending intents. Instead, the collection as a whole sets
                // up a pending intent template, and the individual items set a fillInIntent
                // to create unique behavior on an item-by-item basis.
                Intent toastIntent = new Intent(context, StackWidgetProvider.class);
                // Set the action for the intent.
                // When the user touches a particular view, it will have the effect of
                // broadcasting TOAST_ACTION.
                toastIntent.setAction(StackWidgetProvider.TOAST_ACTION);
                toastIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_ID, appWidgetIds[i]);
                intent.setData(Uri.parse(intent.toUri(Intent.URI_INTENT_SCHEME)));
                PendingIntent toastPendingIntent = PendingIntent.getBroadcast(context, 0, toastIntent,
                    PendingIntent.FLAG_UPDATE_CURRENT);
                rv.setPendingIntentTemplate(R.id.stack_view, toastPendingIntent);

                appWidgetManager.updateAppWidget(appWidgetIds[i], rv);
            }
        super.onUpdate(context, appWidgetManager, appWidgetIds);
        }
    }

##### Setting the fill-in Intent

Your `RemoteViewsFactory` must set a fill-in intent on each item in the collection. This makes it possible to distinguish the individual on-click action of a given item. The fill-in intent is then combined with the `PendingIntent` template in order to determine the final intent that will be executed when the item is clicked.

    public class StackWidgetService extends RemoteViewsService {
        @Override
        public RemoteViewsFactory onGetViewFactory(Intent intent) {
            return new StackRemoteViewsFactory(this.getApplicationContext(), intent);
        }
    }

    class StackRemoteViewsFactory implements RemoteViewsService.RemoteViewsFactory {
        private static final int mCount = 10;
        private List<WidgetItem> mWidgetItems = new ArrayList<WidgetItem>();
        private Context mContext;
        private int mAppWidgetId;

        public StackRemoteViewsFactory(Context context, Intent intent) {
            mContext = context;
            mAppWidgetId = intent.getIntExtra(AppWidgetManager.EXTRA_APPWIDGET_ID,
                    AppWidgetManager.INVALID_APPWIDGET_ID);
        }

        // Initialize the data set.
            public void onCreate() {
                // In onCreate() you set up any connections / cursors to your data source. Heavy lifting,
                // for example downloading or creating content etc, should be deferred to onDataSetChanged()
                // or getViewAt(). Taking more than 20 seconds in this call will result in an ANR.
                for (int i = 0; i < mCount; i++) {
                    mWidgetItems.add(new WidgetItem(i + "!"));
                }
               ...
            }
            ...

            // Given the position (index) of a WidgetItem in the array, use the item's text value in
            // combination with the app widget item XML file to construct a RemoteViews object.
            public RemoteViews getViewAt(int position) {
                // position will always range from 0 to getCount() - 1.

                // Construct a RemoteViews item based on the app widget item XML file, and set the
                // text based on the position.
                RemoteViews rv = new RemoteViews(mContext.getPackageName(), R.layout.widget_item);
                rv.setTextViewText(R.id.widget_item, mWidgetItems.get(position).text);

                // Next, set a fill-intent, which will be used to fill in the pending intent template
                // that is set on the collection view in StackWidgetProvider.
                Bundle extras = new Bundle();
                extras.putInt(StackWidgetProvider.EXTRA_ITEM, position);
                Intent fillInIntent = new Intent();
                fillInIntent.putExtras(extras);
                // Make it possible to distinguish the individual on-click
                // action of a given item
                rv.setOnClickFillInIntent(R.id.widget_item, fillInIntent);

                ...

                // Return the RemoteViews object.
                return rv;
            }
        ...
        }

### Keeping Collection Data Fresh

The following figure illustrates the flow that occurs in an App Widget that uses collections when updates occur. It shows how the App Widget code interacts with the `RemoteViewsFactory`, and how you can trigger updates:

One feature of App Widgets that use collections is the ability to provide users with up-to-date content. For example, consider the Android 3.0 Gmail app widget, which provides users with a snapshot of their inbox. To make this possible, you need to be able to trigger your `RemoteViewsFactory` and collection view to fetch and display new data. You achieve this with the `AppWidgetManager` call `notifyAppWidgetViewDataChanged()`. This call results in a callback to your `RemoteViewsFactory`’s `onDataSetChanged()` method, which gives you the opportunity to fetch any new data. Note that you can perform processing-intensive operations synchronously within the `onDataSetChanged()` callback. You are guaranteed that this call will be completed before the metadata or view data is fetched from the `RemoteViewsFactory`. In addition, you can perform processing-intensive operations within the `getViewAt()` method. If this call takes a long time, the loading view (specified by the `RemoteViewsFactory`’s `getLoadingView()` method) will be displayed in the corresponding position of the collection view until it returns.

↑ Go to top