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中获取输出数据。worker按预期定期运行，只是不返回任何数据。

我的MainActivity：

@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返回的值始终为null。以下是日志记录内容：

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 中获取输出数据的操作很顺利。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);
                    }
                }
            });

接着我成功地从输出数据中获取了数值：

MainActivity: message: This is output message

我已经尝试过将唯一的工作排队和按标签排队，但没有成功。 尝试过WorkManager 2.2.0和1.x，结果相同。

我是否漏掉了什么？从PeriodicWorkRequest获取输出数据是否可能？我做错了什么？

- Target

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WorkManager.getInstance().enqueueUniquePeriodicWork("天气工作器", ExistingPeriodicWorkPolicy.REPLACE, work) 将解决您的问题。对于周期性工作，请使用 REPLACE。 - CHIRANJIT BARDHAN

Answer 1

根据WorkInfo文档，请注意：输出仅适用于终端状态(WorkInfo.State.SUCCEEDED和WorkInfo.State.FAILED)。

对于周期性工作，每次运行都重复使用相同的ID，这意味着工作永远不会到达SUCCEEDED状态-相反，工作立即转换回ENQUEUED状态，等待下一次周期性运行。因此，您所遇到的情况似乎是预期的行为。

如您所见，使用一次性工作不会有这种行为，因为工作实际上会达到SUCCEEDED状态，如果您的一次性工作重新安排相同类型的工作，则每个后续运行都将具有新的ID。另一种选择是不使用输出数据，而是将周期性工作的结果存储在您自己的数据库中。

- ianhanniballake

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救命答案 10/10 - Abdul Mateen

Answer 2

另一种选择是观察中间工人的进度，在你的ServerRequestsWorker中：

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

然后在你的 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);
                }
            }
        });

- Rahmat Ihsan