安卓观察多个MutableLiveData

Question

我有一个MVVM设置，有两个片段通过ViewModel交互。我的SourceFragment正在更新VM中的两个MutableLiveData LatLngs。我的第二个是MapFragment，在其中我用两个LatLng LiveData绘制了一条路由。当活动启动时，两个片段都会被加载。SourceFragment更新LatLngs。在请求绘制路线之前，我需要等待地图加载，并且我有第三个MutableLiveData布尔值，在地图加载后更新。目前，我实现这一点的方法是在我的MapFragment中为这三个viewModel设置三个独立的MutableLiveData观察器，并使用一组if语句来检查何时设置了所有这三个MutableLiveData。我有一种感觉，使用像MediatorLiveData这样的东西可以做得更好，但我还没有找到一个我可以解决的例子。MediatorLiveData或其他东西在这里适用吗？

我的源代码片段

viewModel.setPickupLocation(pickupLatLng);
viewModel.setDestinationLatLng(destinationLatLng());

我的地图片段

@Override
public void onActivityCreated(@NonNull Bundle savedInstanceState) {
    Log.d(TAG, "onActivityCreated: called");
    super.onActivityCreated(savedInstanceState);

    getCustomerOrDriverViewModel();

}

private void initViewModels() { 

    viewModel.getPickupLocation().observe(getViewLifecycleOwner(), new Observer<LatLng>() {
        @Override
        public void onChanged(@NonNull LatLng pickupLocation) {
            Log.d(TAG, "onChanged: from onActivityCreated: called for getPickupLocation");

            if(viewModel.getMapReady().getValue() != null) {
                if(viewModel.getMapReady().getValue()) {
                    resetRoute();

                    setSingleMarker(pickupLocation);
                    if(viewModel.getDestinationLatLng().getValue() != null) {
                        plotRoute(viewModel.getDestinationLatLng().getValue(), pickupLocation);
                    }
                }
            }
        }
    });

    viewModel.getDestinationLatLng().observe(getViewLifecycleOwner(), new Observer<LatLng>() {
        @Override
        public void onChanged(@NonNull LatLng destinationLatLng) {
            Log.d(TAG, "onChanged: from onActivityCreated: called for getPickupLocation");
            if(viewModel.getMapReady().getValue() != null) {
                if(viewModel.getMapReady().getValue()) {
                    resetRoute();

                    if(viewModel.getPickupLocation().getValue() != null) {
                        plotRoute(destinationLatLng, viewModel.getPickupLocation().getValue());
                    }
                }
            }
        }
    });

    viewModel.getMapReady().observe(getViewLifecycleOwner(), new Observer<Boolean>() {
        @Override
        public void onChanged(@NonNull Boolean ready) {
            Log.d(TAG, "onChanged: from onActivityCreated: called for getMapReady");
            if(ready) {
                if(viewModel.getPickupLocation().getValue() != null && viewModel.getDestinationLatLng().getValue() != null) {
                    Log.d(TAG, "onChanged: from onActivityCreated: called for getMapReady: plotting route");
                    resetRoute();
                    plotRoute(viewModel.getDestinationLatLng().getValue(), viewModel.getPickupLocation().getValue());
                }
            }
        }
    });
}

mMap.setOnMapLoadedCallback(new GoogleMap.OnMapLoadedCallback() {
    @Override
    public void onMapLoaded() {
        viewModel.setMapReady(true);
    }
});

我的ViewModel

private MutableLiveData<LatLng> pickupLocation = new MutableLiveData<>();
private MutableLiveData<LatLng> destinationLatLng = new MutableLiveData<>();
private MutableLiveData<Boolean> mapReady = new MutableLiveData<>();

public void setPickupLocation(LatLng input) {
    Log.d(TAG, "setPickupLocation: ");
    pickupLocation.setValue(input);
}

public void setDestinationLatLng(LatLng input) {
    Log.d(TAG, "setPickupLocation: ");
    destinationLatLng.setValue(input);
}

public void setMapReady(Boolean input) {
    Log.d(TAG, "setPickupLocation: ");
    mapReady.setValue(input);
}

public MutableLiveData<LatLng> getPickupLocation() {
    Log.d(TAG, "getPickupLocation: ");
    return pickupLocation;
}

public MutableLiveData<LatLng> getDestinationLatLng() {
    Log.d(TAG, "getDestinationLatLng: ");
    return destinationLatLng;
}

public MutableLiveData<Boolean> getMapReady() {
    Log.d(TAG, "getMapReady: ");
    return mapReady;
}

Answer 1

在MyMapFragment中有3个变量来跟踪每个视图模型请求。在片段创建时使所有3个变量都为空。当每个viewModel请求完成时，更改相应的变量。

然后创建一个helper方法

private void setupData(){
    if(variable1 == null || variable2 == null || variable3 == null){
        return;
    }
    plotRoute(xxxxxx);
}

然后在每个视图模型响应中调用setupData()来代替三重嵌套的if语句检查