使用dagger2的Android生命周期库ViewModel

1> 小智..：

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你需要实现自己的ViewModelProvider.Factory.Google创建了一个示例应用,演示如何将Dagger 2与ViewModels连接.链接.你需要这5件事:

在ViewModel中:

@Inject
public UserViewModel(UserRepository userRepository, RepoRepository repoRepository) {

定义注释:

@Documented
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@MapKey
@interface ViewModelKey {
    Class value();
}

在ViewModelModule中:

@Module
abstract class ViewModelModule {
    @Binds
    @IntoMap
    @ViewModelKey(UserViewModel.class)
    abstract ViewModel bindUserViewModel(UserViewModel userViewModel);

在片段中:

@Inject
ViewModelProvider.Factory viewModelFactory;

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
            userViewModel = ViewModelProviders.of(this, viewModelFactory).get(UserViewModel.class);

厂:

@Singleton
public class GithubViewModelFactory implements ViewModelProvider.Factory {
    private final Map, Provider> creators;

    @Inject
    public GithubViewModelFactory(Map, Provider> creators) {
        this.creators = creators;
    }

    @SuppressWarnings("unchecked")
    @Override
    public  T create(Class modelClass) {
        Provider creator = creators.get(modelClass);
        if (creator == null) {
            for (Map.Entry, Provider> entry : creators.entrySet()) {
                if (modelClass.isAssignableFrom(entry.getKey())) {
                    creator = entry.getValue();
                    break;
                }
            }
        }
        if (creator == null) {
            throw new IllegalArgumentException("unknown model class " + modelClass);
        }
        try {
            return (T) creator.get();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

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您还必须声明:`@Binds abstract ViewModelProvider.Factory bindViewModelFactory(GithubViewModelFactory factory);`在您的ViewModelModule中

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您还需要定义@ViewModelKey https://github.com/googlesamples/android-architecture-components/blob/388a10dd5a814ba6aaa9bf8dee8e7c1c5840b3a5/GithubBrowserSample/app/src/main/java/com/android/example/github/di/ViewModelKey.java

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我相信此答案中缺少一些内容。我仍然让我的工厂为null，Android退回到默认工厂，并产生“没有零参数构造函数”异常。

2> argenkiwi..：

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今天我学会了一种避免为我的ViewModel课程编写工厂的方法:

class ViewModelFactory @Inject constructor(
    private val viewModel: Lazy
) : ViewModelProvider.Factory {
    @Suppress("UNCHECKED_CAST")
    override fun  create(modelClass: Class): T = viewModel.get() as T
}

编辑:正如@Calin在评论中指出的那样,我们Lazy在上面的代码片段中使用Dagger ,而不是Kotlin的.

ViewModel您可以将一个泛型ViewModelFactory注入到您的活动和片段中,而不是注入它,并获取任何实例ViewModel:

class MyActivity : Activity() {

    @Inject
    internal lateinit var viewModelFactory: ViewModelFactory
    private lateinit var viewModel: MyViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        AndroidInjection.inject(this)
        super.onCreate(savedInstanceState)
        this.viewModel = ViewModelProviders.of(this, viewModelFactory)
            .get(MyViewModel::class.java)
        ...
    }

    ...
}

我AndroidInjection.inject(this)和dagger-android库一样使用,但您可以按照自己喜欢的方式注入活动或片段.剩下的就是确保您ViewModel从模块中提供:

@Module
object MyModule {
    @JvmStatic
    @Provides
    fun myViewModel(someDependency: SomeDependency) = MyViewModel(someDependency)
} 

或者将@Inject注释应用于其构造函数:

class MyViewModel @Inject constructor(
    someDependency: SomeDependency
) : ViewModel() {
    ...
}

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啊得到它,是匕首懒惰,而不是从kotlin懒惰:(

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inline fun ViewModelFactory .get(activity:FragmentActivity):T = ViewModelProviders.of(activity,this).get(T :: class.java)