android - ListView 自定义适配器重复项

Question

这个适配器有什么问题，当我向下滚动时，我看到底部有重复的行，然后当再次向上滚动时，我也看到顶部有重复的行，这些行以前不存在，其余的 Data项目没有出现

适配器:

public class ClassesListViewAdapter extends BaseAdapter {
    private Context mContext;
    ArrayList<String> Data = new ArrayList<>();


    public ClassesListViewAdapter(Context context, ArrayList<String> data) {
        Data = data;
        mContext = context;
    }

    @Override
    public Object getItem(int position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public int getCount() {
        return Data.size();
    }
    private class ViewHolder{

        TextView ClassDataTV;

    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = ((Activity)mContext).getLayoutInflater();
        ViewHolder holder;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.classes_list_view_item, parent, false);
            holder = new ViewHolder();
            holder.ClassDataTV = (TextView) convertView.findViewById(R.id.ClassDataTV);
            holder.ClassDataTV.setText(Data.get(position));
            convertView.setTag(holder);
        }else{
            holder=(ViewHolder)convertView.getTag();
        }

        return convertView;
    }
}

下面是我如何使用它:

    ArrayList<String> v = new ArrayList<>();
    v.add("AAAAAAA");
    v.add("WWWWWwW");
    v.add("VVVVVVV");
    v.add("SSSSSSSSS");
    v.add("QQQQQQQQQ");
    v.add("YYYYYYYY");
    v.add("TTTTTTT");
    v.add("UUUUUUUUUU");
    v.add("zzzzzzzzzzzz");
    v.add("CCCCCCCCCC");
    v.add("HHHHHHHHHHH");
    v.add("IIIIIIIIII");
    v.add("PPPPPPPPP");
    mListView.setAdapter(new ClassesListViewAdapter(getActivity(), v));

Answer 1

将以下部分代码放在 if-block 之外，它将得到修复:

  @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = ((Activity)mContext).getLayoutInflater();
        ViewHolder holder;
        if (convertView == null) {
            convertView = inflater.inflate(R.layout.classes_list_view_item, parent, false);
            holder = new ViewHolder();
            holder.ClassDataTV = (TextView) convertView.findViewById(R.id.ClassDataTV);

            convertView.setTag(holder);
        }else{
            holder=(ViewHolder)convertView.getTag();
        }

      // initialize your view here 
        holder.ClassDataTV.setText(Data.get(position));
        return convertView;
    }

ViewHolder 模式背后的逻辑告诉你应该这样做。当您滚动时，一些引用将不会再次创建并且 else block 被调用，因此这会导致您的列表未按预期更新。