Allow retrieving ViewModels from stores by key

[amaksoft]

Sometimes it is necessary to store multiple instances of same ViewModel type in the one ViewModelStore. The only way to resolve this case is to call ViewModelProvider.get(String key, Class<T> modelClass) with a String key parameter. I think we need to add a key parameter to viewmodel extension if possible.

[arnaudgiuliani]

Hello,

Ok I see. Do you have a concrete example on using different instances of the same ViewModel?

[amaksoft]

Sometimes I use generic ViewModels in my projects. Here is an example.
It's a generalized ViewModel for making an HTTP request without creating similar classes for different screens/requests.

Here is how to use it:

val wiewModel: RequestViewModel<User> = ViewModelProviders.of(this).get("UpdateUser", RequestViewModel.class) as RequestViewModel<User>
viewModel.response.observe(this, Observer { resp: Response<User> ->
    showProgress(resp?.status == Response.Status.LOADING)
        when (resp?.status) {
            Response.Status.SUCCESS -> {
                updateUserFields(resp?.data)
            }
            Response.Status.ERROR -> {
                showError(resp?.error)
            }
            Response.Status.LOADING -> {}
        }
})

btSave.setOnCLickListener {
    viewmodel.makeRequest(httpService.updateUser(makeUpdatedUser()))
}

This way you can have dozens of view models of the same type and even same type parameter, but making different requests. I'm not saying it's the best practices, just exploring this pattern. Feel free to use it if you like.
It's merely an example. I'm sure people can think of more ways to use multiple instances of ViewModel of the same type.

[arnaudgiuliani]

Yes I understand. I will make the patch on a next rc version. Can you check it? I will provide it in 0.9.0-rc-3

Can be cool if you have a very small project example to test this key feature.

[amaksoft]

Sure! I can even add a robolectric based unit-test to my PR to test this

[arnaudgiuliani]

I've just redirect your PR on the right branch. Check the conflicting diffs.