ViewModelFactory 将为我们提供来自 ViewModelModule 的正确 ViewModel
public class ViewModelFactory implements ViewModelProvider.Factory {
private final Map<Class<? extends ViewModel>, Provider<ViewModel>> viewModels;
@Inject
public ViewModelFactory(Map<Class<? extends ViewModel>, Provider<ViewModel>> viewModels) {
this.viewModels = viewModels;
}
@Override
public <T extends ViewModel> T create(Class<T> modelClass) {
Provider<ViewModel> viewModelProvider = viewModels.get(modelClass);
if (viewModelProvider == null) {
throw new IllegalArgumentException("model class " + modelClass + " not found");
}
return (T) viewModelProvider.get();
}
}
ViewModelModule 负责将所有 ViewModel 类绑定到
Map<Class<? extends ViewModel>, Provider<ViewModel>> viewModels
@Module
public abstract class ViewModelModule {
@Binds
abstract ViewModelProvider.Factory bindViewModelFactory(ViewModelFactory viewModelFactory);
//You are able to declare ViewModelProvider.Factory dependency in another module. For example in ApplicationModule.
@Binds
@IntoMap
@ViewModelKey(UserViewModel.class)
abstract ViewModel userViewModel(UserViewModel userViewModel);
//Others ViewModels
}
ViewModelKey 是在 Map 中用作键的注解，看起来像
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@MapKey
@interface ViewModelKey {
Class<? extends ViewModel> value();
}
现在您可以创建 ViewModel 并满足图表中所有必要的依赖关系
public class UserViewModel extends ViewModel {
private UserFacade userFacade;
@Inject
public UserViewModel(UserFacade userFacade) { // UserFacade should be defined in one of dagger modules
this.userFacade = userFacade;
}
}
实例化视图模型
public class MainActivity extends AppCompatActivity {
@Inject
ViewModelFactory viewModelFactory;
UserViewModel userViewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
((App) getApplication()).getAppComponent().inject(this);
userViewModel = ViewModelProviders.of(this, viewModelFactory).get(UserViewModel.class);
}
}
并且不要伪造将ViewModelModule添加到modules列表中
@Singleton
@Component(modules = {ApplicationModule.class, ViewModelModule.class})
public interface ApplicationComponent {
//
}