Kotlin 基类中的 ViewModelProviders.get(...)

If you have a BaseFragment defined like this:

public class BaseFragment<T extends ViewModel> extends Fragment {

    @Inject
    protected T viewModel;

}

You can use the ViewModelUtils class from the Architecture Components's Github browser sample to create ViewModel factories.

/**
 * Creates a one off view model factory for the given view model instance.
 */
public class ViewModelUtil {
    private ViewModelUtil() {}
    public static <T extends ViewModel> ViewModelProvider.Factory createFor(T model) {
        return new ViewModelProvider.Factory() {
            @Override
            public <T extends ViewModel> T create(Class<T> modelClass) {
                if (modelClass.isAssignableFrom(model.getClass())) {
                    return (T) model;
                }
                throw new IllegalArgumentException("unexpected model class " + modelClass);
            }
        };
    }
}

In the onActivityCreated method of the BaseFragment you can add

    @Override
    public void onActivityCreated(@Nullable final Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        ViewModelProvider.Factory viewModelFactory = ViewModelUtil.createFor(viewModel);
        ViewModelProviders.of(this, viewModelFactory).get(viewModel.getClass());
    }

这项技术的代码来自this blog post.