Android Architecture Component: How to insert repository parameter

Question

In a viewmodel class, I've seen sample codes where the constructor takes in a repository as a parameter. Like so:

public SampleViewModel(SampleRepository sampleRepository){ ... }

But in the activity, you use this line to create a viewmodel class ViewModelProviders.of(this).get(SampleViewModel.class). How do you pass a repository as a parameter to the viewmodel? I also come across mentioning of "dependency injection". Being an inexperience programmer, can anyone advice if DI is related to my question?

Answer 1

You have to supply a ViewModelProvider.Factory when you get your viewmodel.

ViewModelProviders.of(this, new SampleViewModelFactory(sampleRepo)).get(SampleViewModel.class)

Here's a sample:

class SampleViewModelFactory implements ViewModelProvider.Factory {

    private final SampleRepository repo;

    @Inject
    public SampleViewModelFactory(SampleRepository repo) {
       this.repo = repo;
    }

    @Override
    public SampleViewModel create(Class modelClass) {
        return new SampleViewModel(repo);
    }
}