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。
复制代码代码如下:
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
复制代码代码如下:
// 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.
复制代码代码如下:
// 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（）。
复制代码代码如下:
// 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。
复制代码代码如下:
/*
         * 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。