在Android中的模块之间共享ViewModel实例

Question

I am working on MVVM Architecture. I want to share an instance of view model between module in my android app. when user complete the ride from app module I would like to access my chat module view model instance to perform some db operation ie clear Conversation Entity, etc. I am using Room Database with View Model. ChatActivityNew is an activity in chat module.

App Module Booking Activity

Dialogs.INSTANCE.showRideStatusDialog(mCurrentActivity, new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Dialogs.INSTANCE.dismissDialog();
        Dialogs.INSTANCE.showLoader(mCurrentActivity);
        ChatActivityNew.setMukamalListener(iMukamalCallback);
        dataRepository.requestEndRide(mCurrentActivity, driversDataHandler);
    }
}

Chat Module ChatActivityNew

/**
 * Set the Mukamal Callback listener & call onMukamal abstract
 * method which takes Message view model as a parameter.
 *
 * @param iMukamalCallback is a callback listener.
 */
public static void setMukamalListener(IMukamalCallback iMukamalCallback) {
    mukamalCallback = iMukamalCallback;
    mukamalCallback.onMukamal(mModel);
}

mModel is null because activity is not loaded yet and MessageViewModel is null so how can i access an instance of MessageViewModel.

I have followed the android developer documentation https://developer.android.com/topic/libraries/architecture/viewmodel

Any Help will will be highly appreciable.

EDIT

Dialogs.INSTANCE.showRideStatusDialog(mCurrentActivity, new View.OnClickListener() {
    @Override
    public void onClick(View v) {
          Dialogs.INSTANCE.dismissDialog();
          Dialogs.INSTANCE.showLoader(mCurrentActivity);
          EventBus.getDefault().postSticky(
              new MessageEvent(com.example.chatmodule.utils.Constants.RIDE_COMPLETE)
          );
          dataRepository.requestEndRide(mCurrentActivity, driversDataHandler);
        }
    }

Chat Module Subscribe Method

@Subscribe(threadMode = ThreadMode.MAIN, sticky = true)
    public void onMessageEvent(MessageEvent event) {
        if (mModel != null && event.message.equalsIgnoreCase(RIDE_COMPLETE)){
            mModel.deleteConversation();
            mModel.deleteMessages();
        }
    }

Answer 1

Ideally, you would want to de-couple these view models as much as possible. To achieve what your're trying to do, you'd need an Event Aggregator mechanism.

In your example, your chat module would subscribe to the events of type "NowSave" and your App moudle would publish an event of type "NowSave" when it requires data to be saved.

In the Android world, EventBus looks like the popular library to use for such mechanism: http://greenrobot.org/eventbus/