WorkManager的OneTimeWorkRequest的重试策略/机制是什么

Question

我有以下一次性工作人员.

// Create a Constraints that defines when the task should run
Constraints constraints = new Constraints.Builder()
        .setRequiredNetworkType(NetworkType.UNMETERED)
        .setRequiresBatteryNotLow(true)
        // Many other constraints are available, see the
        // Constraints.Builder reference
        .build();

OneTimeWorkRequest oneTimeWorkRequest =
        new OneTimeWorkRequest.Builder(SyncWorker.class)
                .setConstraints(constraints)
                .addTag(SyncWorker.TAG)
                .build();

根据https://developer.android.com/topic/libraries/architecture/workmanager

// (Returning RETRY tells WorkManager to try this task again
// later; FAILURE says not to try again.)

我想知道,如果SyncWorker继续回来RETRY,重试策略是WorkManager什么？例如,最大重试次数是WorkManager多少？文档不清楚.

Answer 1

默认是BackoffPolicy.EXPONENTIAL.我们只在您RETRY通过返回WorkerResult.RETRY或当您所需的约束Worker现在未得到满足时要求我们重试.因此,例如,如果您需要NETWORK约束,现在设备丢失其活动Network连接 - 那么Worker将停止并自动重试(当满足约束时).

有关更多信息,请查看文档.

Answer 2

以下示例在退出之前对捕获的异常重试 3 次。

class RepeatWorker(context : Context, params : WorkerParameters)
    : Worker(context, params) {

    private fun doSomeThing() {
        // do something
    }

    override fun doWork(): Result {

        if (runAttemptCount > 3) {
            return Result.failure()
        }

        try {
            doSomeThing()
        }
        catch (e: Exception) {
            e.printStackTrace()
            return Result.retry()
        }
        return Result.success()
    }
}

注意：默认 BackoffPolicy 是指数级的，其中 30 秒内进行第一次重试（最小重试周期为 10 秒，最大重试周期不超过 18000 秒/5 小时）。

fun start() : LiveData<WorkInfo> {
    val WORK_NAME = "SingleBackupWorker"

    val constraints = Constraints.Builder()
            .setRequiredNetworkType(NetworkType.CONNECTED)
            .build()

    val work = OneTimeWorkRequestBuilder<BackupWorker>()
            .setConstraints(constraints)
            .setInitialDelay(5, TimeUnit.SECONDS)
            .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 1, TimeUnit.MINUTES)
            .build()

    WorkManager.getInstance().enqueueUniqueWork(WORK_NAME, ExistingWorkPolicy.REPLACE, work)

    return WorkManager.getInstance().getWorkInfoByIdLiveData(work.id)
}