Java 如何将数据从活动或片段传递到viewmodel?
我正在创建一个项目,其中我使用MovieDB api获取数据。为此,我使用MVVM体系结构。从MovieListFragment中,我想将诸如热门、顶级等类别传递给MovieViewModel,以便相应地过滤电影,但在那里我得到了空值 以下是MovieListFragment类:-Java 如何将数据从活动或片段传递到viewmodel?,java,android,android-studio,mvvm,android-mvvm,Java,Android,Android Studio,Mvvm,Android Mvvm,我正在创建一个项目,其中我使用MovieDB api获取数据。为此,我使用MVVM体系结构。从MovieListFragment中,我想将诸如热门、顶级等类别传递给MovieViewModel,以便相应地过滤电影,但在那里我得到了空值 以下是MovieListFragment类:- public class MovieListFragment extends Fragment { private MovieViewModel movieViewModel; private st
public class MovieListFragment extends Fragment {
private MovieViewModel movieViewModel;
private static final String BASE_URL = "https://api.themoviedb.org";
private static final String API_KEY = "API_KEY";
private String category;
private GridView gridView;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_movie_list, container, false);
gridView = rootView.findViewById(R.id.images_grid_view);
movieViewModel = ViewModelProviders.of(this).get(MovieViewModel.class);
movieViewModel.setCategory(category); // from here i am passing value
movieViewModel.getMoviesRepository().observe(getActivity(), new Observer<MovieResults>() { // error line no :- 76
@Override
public void onChanged(MovieResults movieResults) {
final List<MovieResults.ResultsBean> listOfMovies = movieResults.getResults(); // error line no :- 79
MovieListAdapter mAdapter = new MovieListAdapter(getContext(), listOfMovies);
gridView.setAdapter(mAdapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mCallback.onImageSelected(position, listOfMovies);
}
});
}
});
return rootView;
}
public void setCategory(String category) {
this.category = category;
}
}
如果在
movieViewModel.setCategory(category)行中获得字符串category
的null
值
,表示MovieListFragment
的category
字段为空
尝试检查是否调用了片段上的setCategory(String category)
方法
如果不是这样,请详细说明错误。例如,它发生在哪一行等。由于类别是由MovieViewModel的构造函数在setter之前读取的,因此它始终为空
作为方法参数的category呢
public class MovieViewModel extends AndroidViewModel {
private static final String API_KEY = "api_key";
private MovieRepository repository;
private MutableLiveData<MovieResults> listOfMovies = new MutableLiveData<MovieResults>();
public MovieViewModel(@NonNull Application application) {
super(application);
}
public MutableLiveData<MovieResults> getMoviesRepository(category) {
loadData(category);
return listOfMovies;
}
private void loadData(category) {
// Do an asynchronous operation to fetch MovieResults.
repository.getListOfMovies(category, API_KEY);
...
// Receive asynchronous result in callback
// Post the result after getting the asynchronous result.
listOfMovies.postValue(response)
}
}
公共类MovieViewModel扩展了AndroidViewModel{
私有静态最终字符串API_KEY=“API_KEY”;
私人电影收藏库;
私有MutableLiveData listOfMovies=新的MutableLiveData();
公共MoviewModel(@NonNull应用程序){
超级(应用);
}
公共可变LiveData getMoviesRepository(类别){
负荷数据(类别);
归还车辆名单;
}
专用void加载数据(类别){
//执行异步操作以获取MovieResults。
getListOfMovies(类别,API_键);
...
//在回调中接收异步结果
//在获得异步结果后发布结果。
listOfMovies.postValue(响应)
}
}
要获得更详细的实现,需要一个repository类
文件:
必须创建viewmodel工厂才能将数据从活动或片段传递到viewmodel。您可以在MovieListFragment类中的。中引用此内容:
首先删除这一行:moviewmodel.setCategory(category)代码>
并在此处传递“category:moviewmodel.getMoviesRepository(category)
类似下面的代码:
movieViewModel.getMoviesRepository(category).observe(getActivity(), new Observer<MovieResults>() { // error line no :- 76
@Override
public void onChanged(MovieResults movieResults) {
final List<MovieResults.ResultsBean> listOfMovies = movieResults.getResults(); // error line no :- 79
MovieListAdapter mAdapter = new MovieListAdapter(getContext(), listOfMovies);
gridView.setAdapter(mAdapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mCallback.onImageSelected(position, listOfMovies);
}
});
}
});
我不知道为什么它在你的情况下不起作用,但你的问题就是我问题的答案。它在我的项目中运行良好。thanksHowrepository
已创建?repository类与模型类类似,但它使用DAO接口将数据获取和设置到脱机房间数据库,还可以从联机服务器获取和设置数据。我找不到一个好的简单的java示例,但可以在GitHub中看到这个简单的项目。他们使用远程和本地存储库谢谢您的详细回答!是的,我知道它可以是一个房间数据库。我的意思是,它是如何创建的(比如repository=new…
)?因为我们不直接在MovieViewModel
中传递repository
(我不知道它是如何创建的)。这不是代码的问题,而是作者和所有回复者的问题。
public class MovieViewModel extends AndroidViewModel {
private static final String API_KEY = "api_key";
private MovieRepository repository;
private MutableLiveData<MovieResults> listOfMovies = new MutableLiveData<MovieResults>();
public MovieViewModel(@NonNull Application application) {
super(application);
}
public MutableLiveData<MovieResults> getMoviesRepository(category) {
loadData(category);
return listOfMovies;
}
private void loadData(category) {
// Do an asynchronous operation to fetch MovieResults.
repository.getListOfMovies(category, API_KEY);
...
// Receive asynchronous result in callback
// Post the result after getting the asynchronous result.
listOfMovies.postValue(response)
}
}
movieViewModel.getMoviesRepository(category).observe(getActivity(), new Observer<MovieResults>() { // error line no :- 76
@Override
public void onChanged(MovieResults movieResults) {
final List<MovieResults.ResultsBean> listOfMovies = movieResults.getResults(); // error line no :- 79
MovieListAdapter mAdapter = new MovieListAdapter(getContext(), listOfMovies);
gridView.setAdapter(mAdapter);
gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
mCallback.onImageSelected(position, listOfMovies);
}
});
}
});
public class MovieViewModel extends AndroidViewModel {
private static final String API_KEY = "api_key";
private MovieRepository repository;
private MutableLiveData<MovieResults> listOfMovies;
public MovieViewModel(@NonNull Application application) {
super(application);
}
public MutableLiveData<MovieResults> getMoviesRepository(String category) {
Log.d("MovieViewModel", category); // but here i am getting null value
listOfMovies = repository.getListOfMovies(category, API_KEY);
return listOfMovies;
}
}