错误 - "Cannot resolve symbol 'context" 尝试在 RecyclerView 中使用 Glide 加载图像时

Question

我用 Room、ViewModel、LiveData 和 RecyclerView 使用 this tutorial 构建了一个笔记应用程序。一切都运作良好。但是，当我开始为每个笔记实现 select 图像的功能时，RecyclerView 随着添加更多带有图像的笔记变得非常滞后和缓慢。

经过一些研究，我发现使用像Glide和Picasso这样的图像加载框架可以使加载速度更快。因此，我尝试使用 Glide 将图像从 Uri 加载到 RecyclerView 项目中。

NoteAdapter.java

public class NoteAdapter extends ListAdapter<Note, NoteAdapter.NoteHolder> {

Context context;

public NoteAdapter() {
    super(DIFF_CALLBACK);
}

private static final DiffUtil.ItemCallback<Note> DIFF_CALLBACK = new DiffUtil.ItemCallback<Note>() {
    @Override
    public boolean areItemsTheSame(@NonNull Note note, @NonNull Note t1) {
        return note.getId() == t1.getId();
    }

    @Override
    public boolean areContentsTheSame(@NonNull Note note, @NonNull Note t1) {
        return note.getTitle().equals(t1.getTitle()) &&  note.getDescription().equals(t1.getDescription()) && note.getImageUri().equals(t1.getImageUri());
    }
};

private OnItemClickListener listener;

@NonNull
@Override
public NoteHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    View itemView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.note_item, viewGroup, false);
    return new NoteHolder(itemView);
}

@Override
public void onBindViewHolder(@NonNull NoteHolder noteHolder, int i) {
    Note currentNote = getItem(i);
    noteHolder.textViewTitle.setText(currentNote.getTitle());
    noteHolder.textViewDescription.setText(currentNote.getDescription());

    Glide.with(context)
            .load(Uri.parse(currentNote.getImageUri()))
            .fit()
            .centerCrop()
            .into(noteHolder.image);

}

public Note getNoteAt(int position) {
    return getItem(position);
}

class NoteHolder extends RecyclerView.ViewHolder {
    private TextView textViewTitle;
    private TextView textViewDescription;
    private ImageView image;

    public NoteHolder(@NonNull View itemView) {
        super(itemView);
        textViewTitle = itemView.findViewById(R.id.text_view_title);
        textViewDescription = itemView.findViewById(R.id.text_view_description);
        image = itemView.findViewById(R.id.image_view);

        itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int position = getAdapterPosition();

                if (listener != null && position != RecyclerView.NO_POSITION) {
                    listener.onItemClick(getItem(position));
                }
            }
        });
    }
}

public interface OnItemClickListener {
    void onItemClick(Note note);
}

public void setOnItemClickListener(OnItemClickListener listener) {
    this.listener = listener;
}

}

但是，Android Studio 给我以下错误 - Cannot resolve symbol 'context'。我的问题是，我应该为这个论点传递什么背景？此外，非常感谢任何其他在加载图像时使 RecyclerView 更快的建议。谢谢！

PS -我不是专业人士，编程只是一种爱好，所以对于任何误用的术语我深表歉意。

Answer 1

你需要定义全局变量

 Context context ;

并将您的代码更改为以下内容：

public class NoteAdapter extends ListAdapter<Note, NoteAdapter.NoteHolder> {

....
Context context;
@NonNull
@Override
public NoteHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    context = viewGroup.getContext();
View itemView = LayoutInflater.from(context).inflate(R.layout.note_item, viewGroup, false);
    return new NoteHolder(itemView);
}

@Override
public void onBindViewHolder(@NonNull NoteHolder noteHolder, int i) {
    Note currentNote = getItem(i);
    noteHolder.textViewTitle.setText(currentNote.getTitle());
    noteHolder.textViewDescription.setText(currentNote.getDescription());

    Glide.with(context)
            .load(Uri.parse(currentNote.getImageUri()))
            .fit()
            .centerCrop()
            .into(noteHolder.image);

}

....

}

错误 - "Cannot resolve symbol 'context" 尝试在 RecyclerView 中使用 Glide 加载图像时

ERROR - "Cannot resolve symbol 'context" when trying to load images using Glide in RecyclerView

java

android

android-recyclerview

android-glide

listadapter