如何从 Worker class 获取 ViewModel？

Question

我的应用程序中有一个名为 MainActivity 的 Activivity。

MainActivity 与 OnCreate 方法中的一个ViewModel相关联

...
val someViewModel = ViewModelProviders.of(this).get(SomeViewModel::class.java)
...

我用 Workers 做一些背景工作。

val someWork = OneTimeWorkRequestBuilder<LoginWorker>().build() WorkManager.getInstance().beginUniqueWork("SOMEWORK", ExistingWorkPolicy.REPLACE, captivePortalWork).enqueue()
问题来了... worker 例如循环 10 次，每次只休眠一秒钟...所以我们有 10 秒的后台工作. 我想更新 ViewModel 以显示后台工作的进度并每次更新 UI。

A) 我可以从 MainActivity 访问视图模型并观察 worker 但是我只能在进度成功或失败时更新 ViewModel... 这意味着我可以在工作完成 0% 或 100% 时显示进度。

B) 如果我可以从 Worker class 访问 ViewModel，我可以随时更新 ViewModel。但是我不知道怎么...这个方法在 Worker class.
中不起作用
val someWork = ViewModelProviders.of(this).get(SomeViewModel::class.java)

如何从 Worker class 得到 ViewModel？

Answer 1

您不能为此使用 ViewModel。您需要使用自己的房间数据库并向您的 UI 公开一个 LiveData 以显示进度。

Answer 2

您必须将 Worker 输出 Data 的值分配给 ViewModel，并且在您的 Activity 中观察到此数据，如下所示：

工人代码：

public class MyWorker extends Worker {

    public static final String MY_KEY_DATA_FROM_WORKER = "MY_KEY_DATA_FROM_WORKER";

    public MyWorker(@NonNull Context appContext, @NonNull WorkerParameters workerParams) {
        super(appContext, workerParams);
    }

    @NonNull
    @Override
    public Worker.Result doWork() {
        //here do http or database requests
        String result = "my needed result";

        if (result != null) {
            setOutputData(new Data.Builder()
                    .putString(MY_KEY_DATA_FROM_WORKER, result)
                    .build());

            return Worker.Result.SUCCESS;
        }

        return Result.FAILURE;
    }
}

ViewModel 代码：

 public class MyActivityModel extends ViewModel {

    private final MutableLiveData<String> myLiveData = new MutableLiveData<String>();

    public void loadDataFromWorker(LifecycleOwner lifecycleOwner) {
        OneTimeWorkRequest myWorkerReq = new OneTimeWorkRequest.Builder(MyWorker.class)
                .build();

        WorkManager mWorkManager = WorkManager.getInstance();
        mWorkManager
                .beginWith(myWorkerReq)
                .enqueue();

        mWorkManager.getStatusByIdLiveData(myWorkerReq.getId()).observe(lifecycleOwner, new Observer<WorkStatus>() {
            @Override
            public void onChanged(WorkStatus workStatus) {
                if (workStatus.getState().isFinished()) {

                    // here you asign data to ViewModel
                    Data workOutputData = workStatus.getOutputData();
                    myLiveData.setValue(workOutputData.getString(MyWorker .MY_KEY_DATA_FROM_WORKER));
                }
            }
        });
    }

    public MutableLiveData<String> getData() {
        return myLiveData;
    }
  }

Activity 的代码：

//...

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

    //declare model and start loading data in Worker
    MyActivityModel model = ViewModelProviders.of(this).get(MyActivityModel.class);
    model.loadDataFromWorker(this);

    //observe data from model
    model.getData().observe(this, new Observer<String>() {
        @Override
        public void onChanged(String str) {

        //here you get new String value or null if Work failed 

        }
    });
}

//...

Answer 3

来自非常好的 Google 文档的两个附加信息。

a) 如果您来这里是因为没有 viewmodelscope.launch 就无法运行您的任务，请查看 Android“Threading in WorkManager”文档。

b) 这里的问题大概可以用“Observing intermediate Worker progress”来解决。

Answer 4

简而言之，您不想将 ViewModel 暴露给 WorkManager 或 Worker class，而是将百分比暴露给 ViewModel.

WorkManager 2.3.1+ 添加了对设置和观察中间进度的支持。

For Java developers using a ListenableWorker or a Worker, the setProgressAsync() API returns a ListenableFuture; updating progress is asynchronous, given that the update process involves storing progress information in a database. In Kotlin, you can use the CoroutineWorker object's setProgress() extension function to update progress information.

Source

对于 Kotlin，将 CoroutineWorker 与以下内容一起使用：

companion object {
    const val Progress = "Progress"
    private const val delayDuration = 1L
}

override suspend fun doWork(): Result {
    val firstUpdate = workDataOf(Progress to 0)
    val lastUpdate = workDataOf(Progress to 100)
    setProgress(firstUpdate)
    delay(delayDuration)
    setProgress(lastUpdate)
    return Result.success()
}

在你的ViewModel中，你可以这样观察你的进步：

WorkManager.getInstance(applicationContext)
// requestId is the WorkRequest id
.getWorkInfoByIdLiveData(requestId)
.observe(observer, Observer { workInfo: WorkInfo? ->
        if (workInfo != null) {
            val progress = workInfo.progress
            val value = progress.getInt(Progress, 0)
            // Do something with progress information
        }
})

如果您正在使用 WorkContinuation，并且想要总体百分比，我发现最简单的方法是像这样使用 workInfosLiveData：

WorkContinuation.combine(workForSyncingFlights).also {
it.enqueue()
it.workInfosLiveData.asFlow().conflate().collect { listOfWorkInfo ->
    if (listOfWorkInfo.isNullOrEmpty()) return@collect
    listOfWorkInfo.forEach { workInfo ->
        if (workInfo.state.isFinished) {
            val finished = listOfWorkInfo.filter { info -> info.state.isFinished }.size
            val totalPercent = finished.toDouble().div(listOfWorkInfo.size.toDouble()) * 100
        }
    }
}

如何从 Worker class 获取 ViewModel？

How to get a ViewModel from a Worker class?

android

android-architecture-components

android-viewmodel

android-workmanager