报告工作状态

本指南介绍如何报告在后台运行的工作请求的状态 向发送请求的组件传递数据例如，通过该功能， 在 Activity 对象的界面中发出请求。建议您通过 使用 LocalBroadcastManager， 将广播 Intent 对象限制为您自己应用中的组件。

从 JobIntentService 报告状态

要在 JobIntentService 与其他 组件，请先创建一个 Intent，并在其 扩展数据。作为一个选项，您可以向此 Intent。

接下来，通过调用以下代码，发送 Intent LocalBroadcastManager.sendBroadcast()。这会将 Intent 发送到您的应用中已注册接收它的任何组件。如需获取 LocalBroadcastManager 的实例，请调用 getInstance()。

例如：

...
// Defines a custom Intent action
const val BROADCAST_ACTION = "com.example.android.threadsample.BROADCAST"
...
// Defines the key for the status "extra" in an Intent
const val EXTENDED_DATA_STATUS = "com.example.android.threadsample.STATUS"
...
class RSSPullService : JobIntentService() {
    ...
    /*
     * Creates a new Intent containing a Uri object
     * BROADCAST_ACTION is a custom Intent action
     */
    val localIntent = Intent(BROADCAST_ACTION).apply {
        // Puts the status into the Intent
        putExtra(EXTENDED_DATA_STATUS, status)
    }
    // Broadcasts the Intent to receivers in this app.
    LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent)
    ...
}

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 JobIntentService {
...
    /*
     * 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);
...
}

下一步是在Intent 发送原始工作请求的组件。

接收来自 JobIntentService 的状态广播

如需接收广播 Intent 对象，请使用 BroadcastReceiver。在子类中，实现 BroadcastReceiver.onReceive() 回调 方法，LocalBroadcastManager 会在收到 Intent。LocalBroadcastManager 将传入的 Intent 传递给 BroadcastReceiver.onReceive()。

例如：

// Broadcast receiver for receiving status updates from the IntentService.
private class DownloadStateReceiver : BroadcastReceiver() {

    override fun onReceive(context: Context, intent: Intent) {
        ...
        /*
         * Handle Intents here.
         */
        ...
    }
}

// Broadcast receiver for receiving status updates from the IntentService.
private class DownloadStateReceiver extends BroadcastReceiver
{
    // Called when the BroadcastReceiver gets an Intent it's registered to receive
    @Override
    public void onReceive(Context context, Intent intent) {
...
        /*
         * Handle Intents here.
         */
...
    }
}

定义 BroadcastReceiver 后，您便可以定义过滤器 与特定操作、类别和数据匹配的列。为此，请创建 IntentFilter。第一个代码段展示了如何定义过滤器：

// Class that displays photos
class DisplayActivity : FragmentActivity() {
    ...
    override fun onCreate(savedInstanceState: Bundle?) {
        ...
        super.onCreate(savedInstanceState)
        ...
        // The filter's action is BROADCAST_ACTION
        var statusIntentFilter = IntentFilter(BROADCAST_ACTION).apply {
            // Adds a data filter for the HTTP scheme
            addDataScheme("http")
        }
        ...

// 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 statusIntentFilter = new IntentFilter(
                Constants.BROADCAST_ACTION);

        // Adds a data filter for the HTTP scheme
        statusIntentFilter.addDataScheme("http");
        ...

如需注册 BroadcastReceiver 和 IntentFilter 与系统相关联，则获取 LocalBroadcastManager 并调用其 registerReceiver() 方法。接下来的这个代码段展示了如何注册 BroadcastReceiver 及其 IntentFilter：

        // Instantiates a new DownloadStateReceiver
        val downloadStateReceiver = DownloadStateReceiver()
        // Registers the DownloadStateReceiver and its intent filters
        LocalBroadcastManager.getInstance(this)
                .registerReceiver(downloadStateReceiver, statusIntentFilter)
        ...

        // Instantiates a new DownloadStateReceiver
        DownloadStateReceiver downloadStateReceiver =
                new DownloadStateReceiver();
        // Registers the DownloadStateReceiver and its intent filters
        LocalBroadcastManager.getInstance(this).registerReceiver(
                downloadStateReceiver,
                statusIntentFilter);
        ...

单个 BroadcastReceiver 可以处理多种类型的广播 Intent 对象，每个对象都有自己的操作。借助此功能，您可以 为每个操作运行不同的代码，而不必为 每项操作的 BroadcastReceiver。定义另一个 IntentFilter BroadcastReceiver，创建 IntentFilter 并 重复通话 registerReceiver()。 例如：

        /*
         * Instantiates a new action filter.
         * No data filter is needed.
         */
        statusIntentFilter = IntentFilter(ACTION_ZOOM_IMAGE)
        // Registers the receiver with the new filter
        LocalBroadcastManager.getInstance(this)
                .registerReceiver(downloadStateReceiver, statusIntentFilter)

        /*
         * 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(this).registerReceiver(
                downloadStateReceiver,
                statusIntentFilter);

发送广播 Intent 后无法启动或恢复 Activity。针对BroadcastReceiver Activity 会接收和处理 Intent 对象，甚至 当应用位于后台，但不会强制其位于前台时。如果您 想要通知用户当您的应用未正常运行时，后台发生的事件 可见，请使用 Notification。绝不启动 Activity 响应传入的广播 Intent。