Android WorkManager：无法从 PeriodicWorkRequest 获取输出数据

Question

由于某些原因，我无法从 Android WorkManager 的 PeriodicWorkRequest 获取输出数据。工作人员按预期定期运行，只是没有 return 任何数据。

我的主要活动：

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    schedulePeriodicRequests();
}

public void schedulePeriodicRequests() {
    PeriodicWorkRequest workRequest = new PeriodicWorkRequest.Builder(ServerRequestsWorker.class, 15, TimeUnit.MINUTES)
            .build();

    WorkManager workManager = WorkManager.getInstance(MainActivity.this);
    workManager.enqueue(workRequest);
    workManager.getWorkInfoByIdLiveData(workRequest.getId())
            .observe(this, new Observer<WorkInfo>() {
                @Override
                public void onChanged(@Nullable WorkInfo workInfo) {
                    if (workInfo != null) {
                        Log.d(LOG_TAG, "WorkInfo received: state: " + workInfo.getState());
                        String message = workInfo.getOutputData().getString(ServerRequestsWorker.KEY_MESSAGE);
                        Log.d(LOG_TAG, "message: " + message);
                    }
                }
            });
}

我的 ServerRequestsWorker：

public static final String KEY_MESSAGE = "message";

@NonNull
@Override
public Result doWork() {
    Log.d(LOG_TAG, "Worker works");

    Data outputData = new Data.Builder()
            .putString(KEY_MESSAGE, "This is output message")
            .build();

    return Result.success(outputData);
}

workInfo.getOutputData().getString 的值始终为空。这是我在日志中得到的内容：

MainActivity: WorkInfo received: state: ENQUEUED
MainActivity: message: null
ServerRequestsWorker: Worker works
WM-WorkerWrapper: Worker result SUCCESS for Work [ id=5f2beba8-c8bf-4f07-b4ee-e876e95d3cdb, tags={ com.anshmidt.pricemonitor.ServerRequestsWorker } ]
MainActivity: WorkInfo received: state: RUNNING
MainActivity: message: null
MainActivity: WorkInfo received: state: ENQUEUED
MainActivity: message: null

有趣的是，从 OneTimeWorkRequest 获取输出数据工作正常。如果我从 PeriodicWorkRequest 切换到 OneTimeWorkRequest：

    OneTimeWorkRequest serverScraperWorkRequest = new OneTimeWorkRequest.Builder(ServerRequestsWorker.class)
            .build();

    WorkManager workManager = WorkManager.getInstance(MainActivity.this);
    workManager.enqueue(serverScraperWorkRequest);
    workManager.getWorkInfoByIdLiveData(serverScraperWorkRequest.getId())
            .observe(this, new Observer<WorkInfo>() {
                @Override
                public void onChanged(@Nullable WorkInfo workInfo) {
                    if (workInfo != null) {
                        Log.d(LOG_TAG, "WorkInfo received: state: " + workInfo.getState());
                        String message = workInfo.getOutputData().getString(ServerRequestsWorker.KEY_MESSAGE);
                        Log.d(LOG_TAG, "message: " + message);
                    }
                }
            });

，然后我成功地从输出数据中接收到值：

MainActivity: message: This is output message

我试过将独特的工作入队和按标签入队，但没有成功。尝试了 WorkManager 2.2.0 和 1.x，结果是一样的。

我错过了什么吗？甚至可以从 PeriodicWorkRequest 获取输出数据吗？我做错了什么？

Answer 1

根据 WorkInfo documentation:

Note that output is only available for the terminal states (WorkInfo.State.SUCCEEDED and WorkInfo.State.FAILED).

对于周期性工作，每个运行重复使用相同的 ID，这意味着工作永远不会到达 SUCCEEDED - 相反，工作会立即转换回 ENQUEUED，等待为下一个周期运行。因此，您遇到的似乎是预期的行为。

如您所见，使用一次性工作不会有此行为，因为工作实际进行到 SUCCEEDED 和随后的每个运行（如果您的一次性工作是重新安排相同类型的工作）将有一个新的 ID。另一种选择是不使用输出数据，而是将定期工作的结果存储在您自己的数据库中。

Answer 2

另一种选择是Observing intermediate Worker progress

在您的 ServerRequestsWorker 中：

        val outputProgress = workDataOf(KEY_MESSAGE to "This is progress message")
        setProgress(outputProgress)

然后在您的 MainActivity 中：

workManager.getWorkInfoByIdLiveData(workRequest.getId())
        .observe(this, new Observer<WorkInfo>() {
            @Override
            public void onChanged(@Nullable WorkInfo workInfo) {
                if (workInfo != null) {
                    Log.d(LOG_TAG, "WorkInfo received: state: " + workInfo.getState());
                    String message = workInfo.getProgress().getString(ServerRequestsWorker.KEY_MESSAGE);
                    Log.d(LOG_TAG, "message: " + message);
                }
            }
        });

Android WorkManager：无法从 PeriodicWorkRequest 获取输出数据

Android WorkManager: Cannot get output data from PeriodicWorkRequest

java

android

android-workmanager