在某些情況下,您可能需要提供自訂執行緒策略。舉例來說,您可能需要處理以回呼為基礎的非同步作業。WorkManager 透過 ListenableWorker
支援此用途。ListenableWorker
是最基本的工作站 API;Worker
、CoroutineWorker
和 RxWorker
都是來自這個類別。只有在工作開始和停止時,ListenableWorker
才會發出信號,並讓您完全離開執行緒。系統會在主執行緒上叫用啟動工作信號,因此請務必手動前往所選的背景執行緒。
抽象方法 ListenableWorker.startWork()
會傳回 Result
的 ListenableFuture
。ListenableFuture
是一種輕量介面:Future
可提供附加事件監聽器及傳播例外狀況的功能。在 startWork
方法中,您預期會傳回 ListenableFuture
,並在作業完成後以 Result
設定。您可以透過下列兩種方式建立 ListenableFuture
執行個體:
- 如果您使用的是 Guava,請使用
ListeningExecutorService
。 - 否則,請在 Gradle 檔案中加入
councurrent-futures
,並使用CallbackToFutureAdapter
。
如要根據非同步回呼執行某些作業,請執行下列動作:
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; }); } }
如果工作停止,會發生什麼情況?當工作預計停止時,ListenableWorker
的 ListenableFuture
一律會遭到取消。使用 CallbackToFutureAdapter
時,只需新增取消事件監聽器,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; }); } }
以其他程序執行 ReadableWorker
您也可以使用 ListenableWorker
導入 RemoteListenableWorker
,將工作站繫結至特定程序。
RemoteListenableWorker
會繫結至特定程序,其中包含兩個額外的引數,並在建立作業要求時做為輸入資料的一部分:ARGUMENT_CLASS_NAME
和 ARGUMENT_PACKAGE_NAME
。
下列範例說明建立與特定程序繫結的作業要求:
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();
針對每個 RemoteWorkerService
,您必須在 AndroidManifest.xml
檔案中新增服務定義:
<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>