Android App后台服务报告工作状态实例

本节讲运行在后台服务里的工作请求，如何向发送请求者报告状态。推荐用LocalBroadcastManager发送和接收状态，它限制了只有本app才能接收到广播。

从IntentService汇报状态

从IntentService发送工作请求状态给其他组件，先创建一个包含状态和数据的Intent。也可以添加action和URI到intent里。

下一步，调用 LocalBroadcastManager.sendBroadcast()发送Intent,应用中所有注册了接收该广播的接收器都能收到。LocalBroadcastManager.getInstance()获取LocalBroadcastManager实例。

public final class Constants {

    ...

    // Defines a custom Intent action

    public static final String BROADCAST_ACTION =

        "com.example.android.threadsample.BROADCAST";

    ...

    // Defines the key for the status "extra" in an Intent

    public static final String EXTENDED_DATA_STATUS =

        "com.example.android.threadsample.STATUS";

    ...

}

public class RSSPullService extends IntentService {

...

    /*

     * Creates a new Intent containing a Uri object

     * BROADCAST_ACTION is a custom Intent action

     */

    Intent localIntent =

            new Intent(Constants.BROADCAST_ACTION)

            // Puts the status into the Intent

            .putExtra(Constants.EXTENDED_DATA_STATUS, status);

    // Broadcasts the Intent to receivers in this app.

    LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent);

...

}

下一步是接收广播并处理。

接收来自IntentService的广播

接收方式与普通的Broadcast一样，用一个BroadcastReceiver的子类，实现BroadcastReceiver.onReceive()方法

// Broadcast receiver for receiving status updates from the IntentService

private class ResponseReceiver extends BroadcastReceiver

{

    // Prevents instantiation

    private DownloadStateReceiver() {

    }

    // Called when the BroadcastReceiver gets an Intent it's registered to receive

    @

    public void onReceive(Context context, Intent intent) {

...

        /*

         * Handle Intents here.

         */

...

    }

}

定义好了接收器类以后，定义过滤器，匹配指定的action,categorie,data.

// Class that displays photos

public class DisplayActivity extends FragmentActivity {

    ...

    public void onCreate(Bundle stateBundle) {

        ...

        super.onCreate(stateBundle);

        ...

        // The filter's action is BROADCAST_ACTION

        IntentFilter mStatusIntentFilter = new IntentFilter(

                Constants.BROADCAST_ACTION);

 

        // Adds a data filter for the HTTP scheme

        mStatusIntentFilter.addDataScheme("http");

        ...

注册方式稍有不同，用LocalBroadcastManager.registerReceiver()。

  // Instantiates a new DownloadStateReceiver

        DownloadStateReceiver mDownloadStateReceiver =

                new DownloadStateReceiver();

        // Registers the DownloadStateReceiver and its intent filters

        LocalBroadcastManager.getInstance(this).registerReceiver(

                mDownloadStateReceiver,

                mStatusIntentFilter);

        ...

单个BroadcastReceiver可以处理多种类型的广播，这个特性允许你根据不同的action运行不同的代码，而无需为每个action定义一个BroadcastReceiver。

  /*

         * Instantiates a new action filter.

         * No data filter is needed.

         */

        statusIntentFilter = new IntentFilter(Constants.ACTION_ZOOM_IMAGE);

        ...

        // Registers the receiver with the new filter

        LocalBroadcastManager.getInstance(getActivity()).registerReceiver(

                mDownloadStateReceiver,

                mIntentFilter);

发送广播并不会启动或恢复Activity.BroadcastReceiver让Activity能够接收处理数据，包括应用在后台的时候，但不会强制app回到前台。如果你要在app在后台，对用户不可见时，通知用户一个事件发生，用Notification。绝对不要启动一个Activity来响应广播。