Question

基本上我有一个sqlite数据库，允许我插入带有标题的酒店图像。以前我有一个问题，因为我在列表中显示了重复的图像，但感谢上帝，我修复了它。现在图像显示得很好。但是，当我向下或向上滚动列表视图时，应用程序崩溃了。

以下是我初始化自定义适配器的方法。

        adapter = new HotelArrayAdapter(this, R.layout.single_row,
            imageArry);
        ListView dataList = (ListView) findViewById(R.id.list);
        dataList.setAdapter(adapter);

这就是我如何设计它覆盖getView（）方法。

        public class HotelArrayAdapter extends ArrayAdapter<Hotels> {
        Context context;
        int layoutResourceId;
         ArrayList<Hotels> data = new ArrayList<Hotels>();
         public HotelArrayAdapter(Context context, int layoutResourceId,
        ArrayList<Hotels> data) {
        super(context, layoutResourceId, data);
        // TODO Auto-generated constructor stub
        this.layoutResourceId=layoutResourceId;
        this.context = context;
        this.data = data;
       }
       @Override
       public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        View row = convertView;

        ImageHolder holder = null;

        if(row==null){
        LayoutInflater inflater =(LayoutInflater)     
        ((Activity)context).getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        row = inflater.inflate(layoutResourceId, parent,false);

        holder = new ImageHolder();
        holder.txtTitle = (TextView)row.findViewById(R.id.titleView);
        holder.imgIcon=(ImageView)row.findViewById(R.id.iconView);
    }
        Hotels picture = data.get(position);
        holder.txtTitle.setText(picture._name);
        //convert byte to bitmap take from contact class

        byte[] outImage=picture._image;
        ByteArrayInputStream imageStream = new ByteArrayInputStream(outImage);
        Bitmap theImage = BitmapFactory.decodeStream(imageStream);
        holder.imgIcon.setImageBitmap(theImage);
    return row;
   }
    static class ImageHolder
    {
        ImageView imgIcon;
        TextView txtTitle;
    }

 }

最后是logcat的输出 12-12 19：43：20.665：E / MessageQueue-JNI（1183）：java.lang.NullPointerException

         12-12 19:43:20.665: E/MessageQueue-JNI(1183):  at 
         athens.tourist.guide.HotelArrayAdapter.getView(HotelArrayAdapter.java:44)

         12-12 19:43:20.665: E/MessageQueue-JNI(1183):  at 
         athens.tourist.guide.HotelArrayAdapter.getView(HotelArrayAdapter.java:44)
         12-12 19:43:20.665: E/MessageQueue-JNI(1183):  at   
         android.widget.AbsListView.obtainView(AbsListView.java:2143)

         12-12 19:43:20.665: E/MessageQueue-JNI(1183):  at  
         android.widget.ListView.makeAndAddView(ListView.java:1831)

         12-12 19:43:20.665: E/MessageQueue-JNI(1183):  at 
         android.widget.ListView.fillUp(ListView.java:708)

Answer 1

应用程序崩溃，因为convertView只为null一次。尝试将holder对象存储为convertView的标记，然后检索它。 e.g

ImageHolder holder = null;

if(row==null){
    LayoutInflater inflater =(LayoutInflater)     
    ((Activity)context).getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    row = inflater.inflate(layoutResourceId, parent,false);

    holder = new ImageHolder();
    holder.txtTitle = (TextView)row.findViewById(R.id.titleView);
    holder.imgIcon=(ImageView)row.findViewById(R.id.iconView);
    row.setTag(holder);
} 
holder = (ImageHolder) row.getTag();

Answer 2

主要问题是当行不为空时，你永远不会初始化持有者所以，这是null并启动 NullPointerException 。

尝试更改此代码片段：

ImageHolder holder = null;

if(row==null){
   LayoutInflater inflater =(LayoutInflater)     
       ((Activity)context).getSystemService(Context.LAYOUT_INFLATER_SERVICE);
   row = inflater.inflate(layoutResourceId, parent,false);

  holder = new ImageHolder();
  holder.txtTitle = (TextView)row.findViewById(R.id.titleView);
  holder.imgIcon=(ImageView)row.findViewById(R.id.iconView);
}

对于这个：

ImageHolder holder = null;

if(row==null){
   LayoutInflater inflater =(LayoutInflater)     
       ((Activity)context).getSystemService(Context.LAYOUT_INFLATER_SERVICE);
   row = inflater.inflate(layoutResourceId, parent,false);

  holder = new ImageHolder();
  holder.txtTitle = (TextView)row.findViewById(R.id.titleView);
  holder.imgIcon=(ImageView)row.findViewById(R.id.iconView);
  row.setTag(holder);
} else {
    holder = (ImageHolder) row.getTag();
}

当我向下或向上滚动时Listview崩溃

2 个答案: