在某些情况下,您可能需要提供自定义线程策略。例如,您可能需要处理基于回调的异步操作。WorkManager 使用 ListenableWorker
支持此用例。ListenableWorker
是最基础的工作器 API;Worker
、CoroutineWorker
和 RxWorker
都派生自此类别。ListenableWorker
仅发出工作何时开始和停止的信号,线程处理完全由您决定。启动工作信号在主线程上调用,因此手动切换到您选择的后台线程非常重要。
抽象方法 ListenableWorker.startWork()
返回一个 Result
的 ListenableFuture
。ListenableFuture
是一个轻量级接口:它是一个 Future
,提供附加监听器和传播异常的功能。在 startWork
方法中,您应该返回一个 ListenableFuture
,一旦操作完成,您将使用操作的 Result
来设置它。您可以通过以下两种方式之一创建 ListenableFuture
实例
- 如果您使用 Guava,请使用
ListeningExecutorService
。 - 否则,在您的 Gradle 文件中包含
councurrent-futures
并使用CallbackToFutureAdapter
。
如果您想基于异步回调执行一些工作,您可以这样做
Kotlin
class CallbackWorker( context: Context, params: WorkerParameters ) : ListenableWorker(context, params) { override fun startWork(): ListenableFuture<Result> { return CallbackToFutureAdapter.getFuture { completer -> val callback = object : Callback { var successes = 0 override fun onFailure(call: Call, e: IOException) { completer.setException(e) } override fun onResponse(call: Call, response: Response) { successes++ if (successes == 100) { completer.set(Result.success()) } } } repeat(100) { downloadAsynchronously("https://example.com", callback) } callback } } }
Java
public class CallbackWorker extends ListenableWorker { public CallbackWorker(Context context, WorkerParameters params) { super(context, params); } @NonNull @Override public ListenableFuture<Result> startWork() { return CallbackToFutureAdapter.getFuture(completer -> { Callback callback = new Callback() { int successes = 0; @Override public void onFailure(Call call, IOException e) { completer.setException(e); } @Override public void onResponse(Call call, Response response) { successes++; if (successes == 100) { completer.set(Result.success()); } } }; for (int i = 0; i < 100; i++) { downloadAsynchronously("https://www.example.com", callback); } return callback; }); } }
如果您的工作被停止会怎样?当工作预期停止时,ListenableWorker
的 ListenableFuture
总是被取消。使用 CallbackToFutureAdapter
,您只需添加一个取消监听器,如下所示
Kotlin
class CallbackWorker( context: Context, params: WorkerParameters ) : ListenableWorker(context, params) { override fun startWork(): ListenableFuture<Result> { return CallbackToFutureAdapter.getFuture { completer -> val callback = object : Callback { var successes = 0 override fun onFailure(call: Call, e: IOException) { completer.setException(e) } override fun onResponse(call: Call, response: Response) { ++successes if (successes == 100) { completer.set(Result.success()) } } } completer.addCancellationListener(cancelDownloadsRunnable, executor) repeat(100) { downloadAsynchronously("https://example.com", callback) } callback } } }
Java
public class CallbackWorker extends ListenableWorker { public CallbackWorker(Context context, WorkerParameters params) { super(context, params); } @NonNull @Override public ListenableFuture<Result> startWork() { return CallbackToFutureAdapter.getFuture(completer -> { Callback callback = new Callback() { int successes = 0; @Override public void onFailure(Call call, IOException e) { completer.setException(e); } @Override public void onResponse(Call call, Response response) { ++successes; if (successes == 100) { completer.set(Result.success()); } } }; completer.addCancellationListener(cancelDownloadsRunnable, executor); for (int i = 0; i < 100; ++i) { downloadAsynchronously("https://www.example.com", callback); } return callback; }); } }
在不同进程中运行 ListenableWorker
您还可以通过使用 ListenableWorker
的实现 RemoteListenableWorker
将工作器绑定到特定进程。
RemoteListenableWorker
使用您在构建工作请求时作为输入数据提供给定的两个额外参数:ARGUMENT_CLASS_NAME
和 ARGUMENT_PACKAGE_NAME
来绑定到特定进程。
以下示例演示了构建绑定到特定进程的工作请求
Kotlin
val PACKAGE_NAME = "com.example.background.multiprocess" val serviceName = RemoteWorkerService::class.java.name val componentName = ComponentName(PACKAGE_NAME, serviceName) val data: Data = Data.Builder() .putString(ARGUMENT_PACKAGE_NAME, componentName.packageName) .putString(ARGUMENT_CLASS_NAME, componentName.className) .build() return OneTimeWorkRequest.Builder(ExampleRemoteListenableWorker::class.java) .setInputData(data) .build()
Java
String PACKAGE_NAME = "com.example.background.multiprocess"; String serviceName = RemoteWorkerService.class.getName(); ComponentName componentName = new ComponentName(PACKAGE_NAME, serviceName); Data data = new Data.Builder() .putString(ARGUMENT_PACKAGE_NAME, componentName.getPackageName()) .putString(ARGUMENT_CLASS_NAME, componentName.getClassName()) .build(); return new OneTimeWorkRequest.Builder(ExampleRemoteListenableWorker.class) .setInputData(data) .build();
对于每个 RemoteWorkerService
,您还需要在 AndroidManifest.xml
文件中添加服务定义
<manifest ... > <service android:name="androidx.work.multiprocess.RemoteWorkerService" android:exported="false" android:process=":worker1" /> <service android:name=".RemoteWorkerService2" android:exported="false" android:process=":worker2" /> ... </manifest>