相关疑难解决方法(0)

我正在尝试使用Android架构组件编写示例应用程序,但即使在尝试了几天之后我也无法使用它.它给了我以上例外.

生命周期所有者: -

public class MainActivity extends LifecycleActivity {

    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = findViewById(R.id.tv_user);
        PostViewModel viewModel = ViewModelProviders.of(this).get(PostViewModel.class);
        viewModel.loadPosts();
        viewModel.getPost().observe(this, new Observer<Post>() {
            @Override
            public void onChanged(@Nullable Post post) {
                if(post != null) {
                    textView.setText(post.toString());
                }
            }
        });
    }
}

视图模型: -

public class PostViewModel extends ViewModel {
    private MediatorLiveData<Post> post;
    private PostRepository postRepo;

    PostViewModel() {
        post = new MediatorLiveData<>();
        postRepo = new PostRepository();
    }

    public LiveData<Post> loadPosts() {
        post.addSource(postRepo.getPost(),
                post -> this.post.setValue(post)
        ); …

我正在使用dagger2库.每当我试图运行我的项目时,都表示无法创建视图模型类的实例.

我正在尝试创建实例的主要活动

   ((MovieApplication) getApplication()).getAppComponent().inject(this);
    mViewModel = ViewModelProviders.of(this).get(MoviesDataViewModel.class);

我的工厂班

public class ViewModelFactory implements ViewModelProvider.Factory {
private MoviesDataViewModel mViewModel;

@Inject
public ViewModelFactory(MoviesDataViewModel viewModel) {
    this.mViewModel = viewModel;
}

@Override
public <T extends ViewModel> T create(Class<T> modelClass) {
    if (modelClass.isAssignableFrom(MoviesDataViewModel.class)) {
        return (T) mViewModel;
    }
    throw new IllegalArgumentException("Unknown class name");
}

我的日志

  Caused by: java.lang.RuntimeException: Cannot create an instance of class com.moviedata.viewmodel.MoviesDataViewModel
                                                               at android.arch.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:145)
                                                               at android.arch.lifecycle.ViewModelProviders$DefaultFactory.create(ViewModelProviders.java:143)
                                                               at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:128)
                                                               at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:96)
                                                               at com.moviedata.ui.MainActivity.onCreate(MainActivity.java:28)
                                                               at android.app.Activity.performCreate(Activity.java:6321)
                                                               at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108)
                                                               at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426)
                                                               at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2535) 
                                                               at android.app.ActivityThread.access$1100(ActivityThread.java:154) 
                                                               at …

我正在创建一个应用程序来扫描条形码并将该信息使用 Android 视图模型和 LiveData 获取到房间数据库中。这是错误信息

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.davin.scoutingapp2019/com.example.davin.scoutingapp2019.DataDisplay}: java.lang.RuntimeException: Cannot create an instance of class com.example.davin.scoutingapp2019.TeamViewModel
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2659)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2724)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1473)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6123)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)
 Caused by: java.lang.RuntimeException: Cannot create an instance of class com.example.davin.scoutingapp2019.TeamViewModel
    at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:207)
    at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134)
    at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102)
    at com.example.davin.scoutingapp2019.DataDisplay.onCreate(DataDisplay.java:30)
    at android.app.Activity.performCreate(Activity.java:6672)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1140)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2612)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2724) 
    at android.app.ActivityThread.-wrap12(ActivityThread.java) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1473) 
    at android.os.Handler.dispatchMessage(Handler.java:102) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6123) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at …