在 Activity 或 Fragment 之外获取 ViewModel 实例的正确方法 [英] The correct way to obtain a ViewModel instance outside of an Activity or a Fragment

问题描述

我正在构建一个位置应用程序，我在其中显示来自 MainActivity 中 Room 数据库的背景位置.我可以通过调用获得一个 ViewModel

I'm building a location app where I display background locations from a Room database in my MainActivity. I can get a ViewModel by calling

locationViewModel = ViewModelProviders.of(this).get(LocationViewModel.class);
locationViewModel.getLocations().observe(this, this);

当我通过 BroadCastReceiver 接收位置更新时，应将周期性背景位置保存到 Room 数据库中.它们应该通过调用 locationViewModel.getLocations().setValue()

Periodic background locations should be saved to the Room database when I receive location updates via a BroadCastReceiver. They should be saved by calling locationViewModel.getLocations().setValue()

public class LocationUpdatesBroadcastReceiver extends BroadcastReceiver {

    static final String ACTION_PROCESS_UPDATES =
            "com.google.android.gms.location.sample.backgroundlocationupdates.action" +
                    ".PROCESS_UPDATES";

    @Override
    public void onReceive(Context context, Intent intent) {
        if (intent != null) {
            final String action = intent.getAction();
            if (ACTION_PROCESS_UPDATES.equals(action)) {
                LocationResult result = LocationResult.extractResult(intent);
                if (result != null) {
                    List<Location> locations = result.getLocations();
                    List<SavedLocation> locationsToSave = covertToSavedLocations(locations)
                    //Need an instance of LocationViewModel to call locationViewModel.getLocations().setValue(locationsToSave)
                }
            }
        }
    }
}

问题是我应该如何在像这个 BroadcastReceiver 这样的非活动类中获取 LocationViewModel 实例?调用 locationViewModel = ViewModelProviders.of(context).get(LocationViewModel.class) 是否正确，其中 context 是我从 onReceive (Context context, Intent intent) 接收的上下文 广播接收器?

Question is how should I get the LocationViewModel instance in a non-activity class like this BroadcastReceiver? Is it correct to call locationViewModel = ViewModelProviders.of(context).get(LocationViewModel.class) where context is the context that I receive from onReceive (Context context, Intent intent) of the BroadcastReceiver?

获取ViewModel后，是否需要使用LiveData.observeForever 和 LiveData.removeObserver 因为 BroadcastReceiver 不是 LifecycleOwner?

After getting the ViewModel, do I need to use LiveData.observeForever and LiveData.removeObserver since the BroadcastReceiver is not a LifecycleOwner?

推荐答案

问题是我应该如何在一个像这个 BroadcastReceiver 这样的非活动类?

Question is how should I get the LocationViewModel instance in a non-activity class like this BroadcastReceiver?

你不应该那样做.它糟糕的设计实践.

You shouldn't do that. Its bad design practice.

调用locationViewModel是否正确=ViewModelProviders.of(context).get(LocationViewModel.class) 其中上下文是我从 onReceive 收到的上下文(上下文上下文，意图意图)的广播接收器?

Is it correct to call locationViewModel = ViewModelProviders.of(context).get(LocationViewModel.class) where context is the context that I receive from onReceive (Context context, Intent intent) of the BroadcastReceiver?

没有.没用的

您可以通过以下方式实现您想要的结果:

在单独的单例类中将 Room DB 操作与 ViewModel 分开.在 ViewModel 和任何其他需要的地方使用它.当接收到 Broadcast 时，通过这个单例类而不是 ViewModel 将数据写入 DB.

Separate your Room DB operation from ViewModel in a separate singleton class. Use it in ViewModel and any other place required. When Broadcast is received, write data to DB through this singleton class rather than ViewModel.

如果您正在观察 Fragment 中的 LiveData，那么它也会更新您的视图.

If you are observing for the LiveData in your Fragment, then it will update your views too.

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