Android MVVM体系结构-ViewModel中的Android参考/导入

Question

Based on the idea that you should not pass and Android view's or other pure Android components to ViewModel , or have android imports there, consider the next use case:

From my Fragment I want to launch some sort of image processing action and for that I need to initialize my object with the current xml view where I want to show the result. So I create it on the ``Fragment side with the view component and then pass that object over to ViewModel .

My problems are:

1. I'm passing to ViewModel an object with already reference to an Android views.

2. The logic in ViewModel creates a Bitmap and after processing it return that bitmap to the Fragment that observes it, as a result I have reference to some Android Bitmap libraries inside my ViewModel

How to avoid referencing Android stuff in ViewModel if I need the work to be done there?

Answer 1

If I understood you correctly, you are inflating your views in the Fragment , then you generate the bitmap in your ViewModel , and then you pass it back and set it in your Fragment , and in the process you need to pass something more to the ViewModel than just Application instance. If that's the case you need to use the ViewModelFactory . In short, you will write a small class that will create the ViewModel for you, and then you pass it to ViewModelProviders.of(this, ...) as a second parameter.

The usage is shown in this answer. If you look around you should also be able to find its usage in Google samples .