android – Activity with multiple ViewModels-ThrowExceptions

Exception or error:

I have an Activity that contains 3 RecyclerViews. I need populate RecyclerViews with data from remote repository (3 different requests). Can I use multiple ViewModels in the Activity, or is there any better solution (best practice).

How to solve:

In this case I would recommend to use one view model which populates three different LiveData objects. This way the UI can get updated whenever one of your three requests gets a response. For details how to use a RecyclerView with LiveData take a look into the Google Example.

I think having multiple viewmodels per activity only increases complexity and I do not see any value in doing that.

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According to the open/closed principle, you should create three different ViewModels. The complexity isn’t increased that much, and you are gaining the ability to move one ViewModel (or just reuse it) with the corresponding RecyclerView to the another Activity very easily.

Of course, sometimes breaking rules makes sense – for example if you know, there is no chance, that RecyclerView will be reused or moved to another screen, and then you can go for simpler solution with one ViewModel.

The same situation if the ViewModel (even with the 3 lists) is likely to stay always very simple (just three LiveData fields, just a few lines of code to populate them), you can break this rule.

However violation of O/CP is not a good practice – it’s just a conscious breaking of rule.

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I got two recyclerview in a fragment. I think that use two ViewModels would be better. Cause different recyclerviews got their own data request, and state handling especially connections error.
In this case separate into different ViewModels would not increase the the complexity, but I think it well fit the rule of decupling

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Even simpler, you can have one ViewModel, that uses one service class, which in turn uses the three repositories to get the data. For example:

XActivity –> XViewModel –> XService –> {Arepository, Brepository, Crepository}

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