Question

中的CursorRecyclerViewAdapter

当我在recyclerview中使用单一视图类型时它工作正常。但是如果我使用多个视图类型，我会崩溃说int android.support.v7.widget.RecyclerView$ViewHolder.mItemViewType null object reference

我使用以下代码扩展CursorRecyclerViewAdapter

public class PostCursorAdapter extends CursorRecyclerViewAdapter<RecyclerView.ViewHolder> {

private static final int VIEW_HOLDER_TYPE_1=1;
private static final int VIEW_HOLDER_TYPE_2=2;
private Integer viewtype=0;

public PostCursorAdapter(Context context,Cursor cursor){
    super(context,cursor);

}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, Cursor cursor) {
    PostItem postitem = PostItem.fromCursor(cursor);
    Log.d("PostItem",postitem.toString());
        int viewtype=1;

    if (postitem.isFromMe()==true){
       viewtype=1;
      }
     else {
       viewtype=2;
      }

    switch (viewtype) {

        case VIEW_HOLDER_TYPE_1:
            ViewHolder_Type1 viewholder1 = (ViewHolder_Type1) holder;
            TextView mytimeView = (TextView) viewholder1.mytimeTextView;
            mytimeView.setText(postitem.getPostTime());
            TextView mymsgView = (TextView) viewholder1.mymessageTextView;
            mymsgView.setText(postitem.getPostMsg());
            break;

        case VIEW_HOLDER_TYPE_2:
            ViewHolder_Type2 viewholder2 = (ViewHolder_Type2) holder;
            TextView timeView = (TextView) viewholder2.timeTextView;
            timeView.setText(postitem.getPostTime());
            TextView msgView = (TextView) viewholder2.messageTextView;
            msgView.setText(postitem.getPostMsg());
            break;

        default:
            break;
    }
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    View v;

    switch (viewType) {

        case VIEW_HOLDER_TYPE_1:
            v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.mypost, parent, false);
            ViewHolder_Type1 vh1 = new ViewHolder_Type1(v);
            return vh1;

        case VIEW_HOLDER_TYPE_2:
            v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.post, parent, false);
            ViewHolder_Type2 vh2 = new ViewHolder_Type2(v);
            return vh2;

        default:
            break;
    }

    return null;
}
public static class ViewHolder_Type1 extends RecyclerView.ViewHolder {
    public TextView mymessageTextView, mytimeTextView;
    public ViewHolder_Type1(View v) {
        super(v);
        this.mymessageTextView = (TextView) v.findViewById(R.id.mymessageTextView);
        this.mytimeTextView = (TextView) v.findViewById(R.id.mytimeTextView);
    }


}

public static class ViewHolder_Type2 extends RecyclerView.ViewHolder {
    public TextView messageTextView, timeTextView;
    public ViewHolder_Type2(View v) {
        super(v);
        this.messageTextView = (TextView) v.findViewById(R.id.messageTextView);
        this.timeTextView = (TextView) v.findViewById(R.id.timeTextView);
    }
}}

Answer 1

问题（我认为）是RecyclerView没有任何线索，你有多种视图类型。

解决方案可能是覆盖getItemViewType。但是，当您只能从Cursor中决定viewType时，这可能会很棘手。如果是这种情况，我建议您覆盖GetItemViewType类中的CursorRecyclerViewAdapter方法。

@Override
public int getItemViewType(int position){
    int viewType = cursor // somehow determine the viewType;
    return viewType;
}

Answer 2

您应该实现getItemViewType以返回Recycler视图中每个位置的正确ViewType。请参阅教程here。

具有多个视图类型的CursorRecyclerViewAdapter

2 个答案: