如何将片段的上下文转换为 LifecycleOwner？

Question

我有以下情况。我有一个 activity 包含一个片段。在这个片段中，我显示了一些来自后端数据库的记录。我也在使用如下所示的适配器：

public class MovieAdapter extends PagedListAdapter<Movie, MovieAdapter.MovieViewHolder> {
    private Context context;

    public MovieAdapter(Context context) {this.context = context;}

    @NonNull
    @Override
    public MovieViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        //Create the view
    }

    @Override
    public void onBindViewHolder(@NonNull final MovieViewHolder holder, int position) {
        Movie movie = getItem(position);
        String title = movie.title;
        holder.titleTextView.setText(title);

        MovieRepository movieRepository = new MovieRepository(context);
        LiveData<Movie> liveData = movieRepository.retrieveFavoriteMovie(movie.id);
        liveData.observe(context, m -> { //Error
            if(m != null) {
                boolean favorite = m.favorite;
                if(favorite) {
                    //Do something
                } else {
                    //Do something else
                }
            }
        });
    }

    class MovieViewHolder extends RecyclerView.ViewHolder {
        ImageView favoriteImageView;
        TextView titleTextView;

        MovieViewHolder(View itemView) {
            super(itemView);
            titleTextView = itemView.findViewById(R.id.title_text_view);                favoriteImageView = itemView.findViewById(R.id.favorite_image_view);
        }
    }
}

在 onBindViewHolder 中，我试图检查 Romm 数据库中是否存在特定电影，但我收到此错误：

Wrong 1st argument type. Found: 'android.content.Context', required: 'android.arch.lifecycle.LifecycleOwner'

那么如何将片段的上下文转换为 LifecycleOwner 以便我可以在我的方法中将其用作参数？

Answer 1

android.content.Context 没有实现 android.arch.lifecycle.LifecycleOwner.

您必须传递 AppCompatActivity 的实例，它实现了 android.arch.lifecycle.LifecycleOwner（或任何其他 class 实现的实例）。

或转换 (AppCompatActivity) context，当 context 是 instanceof AppCompatActivity。要以可靠的方式从上下文中获取 Activity，请检查

Answer 2

为找出上面建议的解决方案的人发布这个，下面我为 kotlin android

添加了 this 的简写扩展版本

private fun Context?.getLifeCycleOwner() : AppCompatActivity? = when {
    this is ContextWrapper -> if (this is AppCompatActivity) this else this.baseContext.getLifeCycleOwner()
    else -> null
}

片段中上述扩展的用法如下：

private var mainActivityContext: Context? = null //class level variable

//below statement called after context variable assigned / OnCreate
mainActivityContext?.getLifeCycleOwner()?.let { lifeCycleOwner ->
            YourViewModel.liveDataReturningMethod(text.toString())
                .observe(lifeCycleOwner , Observer { x ->
                    //your logic here...
                })
        }

如何将片段的上下文转换为 LifecycleOwner？

How to transform the context of fragment into a LifecycleOwner?

java

android

android-room

android-livedata

片段中上述扩展的用法如下：