Question

我使用ListView创建了一个景点列表。程序运行并显示输出但在滚动列表时它会关闭一个力。我在这里发布我的代码。请给我一些建议。

package com.example.attraction;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.media.Image;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.HashMap;



public class MainActivity extends Activity {

    private ListView listView;
    private ArrayList<HashMap<String,Object>> data;
    private ListAdapter adapter;
    @Override
    public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    listView = (ListView) findViewById(R.id.listView);

    data = new ArrayList<HashMap<String, Object>>();
    prePareListData();
    adapter = new ListAdapter(this,data);
    listView.setAdapter(adapter);
 }
       private void prePareListData(){

    HashMap<String,Object> row1 = new HashMap<String, Object>();
    row1.put("ID",1);
    row1.put("IMAGE",R.drawable.taj);
    row1.put("NAME","Taj Mahal");
    row1.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row1);

    HashMap<String,Object> row2 = new HashMap<String, Object>();
    row2.put("ID",2);
    row2.put("IMAGE",R.drawable.mehtab_baug);
    row2.put("NAME","Mehtab Bagh");
    row2.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row2);

    HashMap<String,Object> row3 = new HashMap<String, Object>();
    row3.put("ID",3);
    row3.put("IMAGE",R.drawable.ram_baugh);
    row3.put("NAME","Ram bagh");
    row3.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row3);

    HashMap<String,Object> row4 = new HashMap<String, Object>();
    row4.put("ID",4);
    row4.put("IMAGE",R.drawable.agra_fort);
    row4.put("NAME","Agra Fort");
    row4.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row4);


    HashMap<String,Object> row5 = new HashMap<String, Object>();
    row4.put("ID",5);
    row4.put("IMAGE",R.drawable.musamman_burj);
    row4.put("NAME","Musamman Burj");
    row4.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row5);

    HashMap<String,Object> row6 = new HashMap<String, Object>();
    row5.put("ID",6);
    row5.put("IMAGE",R.drawable.tomb_of_akbar_the_great);
    row5.put("NAME","Tomb of Akbar The Great");
    row5.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row6);


    HashMap<String,Object> row7 = new HashMap<String, Object>();
    row6.put("ID",7);
    row6.put("IMAGE",R.drawable.tomb_of_itmad_ud_daula);
    row6.put("NAME","Tomb of Itmad Ud Daula");
    row6.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row7);

    HashMap<String,Object> row8 = new HashMap<String, Object>();
    row7.put("ID",8);
    row7.put("IMAGE",R.drawable.fatepur_sikri);
    row7.put("NAME","Fatehpur Sikri");
    row7.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row8);

   HashMap<String,Object> row9 = new HashMap<String, Object>();
    row8.put("ID",9);
    row8.put("IMAGE",R.drawable.panch_mahal);
    row8.put("NAME","Panch Mahal");
    row8.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row9);

    HashMap<String,Object> row10 = new HashMap<String, Object>();
    row9.put("ID",10);
    row9.put("IMAGE",R.drawable.jamma_masjid);
    row9.put("NAME","Jamma Masjid");
    row9.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row10);


    HashMap<String,Object> row11 = new HashMap<String, Object>();
    row10.put("ID",11);
    row10.put("IMAGE",R.drawable.chini_ka_rauza);
    row10.put("NAME","Chini ka Rauza");
    row10.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row11);


    HashMap<String,Object> row12 = new HashMap<String, Object>();
    row10.put("ID",12);
    row10.put("IMAGE",R.drawable.mankameshwar_temple);
    row10.put("NAME","Mankameshwar Temple");
    row10.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row12);


    HashMap<String,Object> row13 = new HashMap<String, Object>();
    row10.put("ID",13);
    row10.put("IMAGE",R.drawable.tomb_of_mariam);
    row10.put("NAME","Tomb of Mariam Zamani");
    row10.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row13);

    HashMap<String,Object> row14 = new HashMap<String, Object>();
    row10.put("ID",14);
    row10.put("IMAGE",R.drawable.guru_ka_tal);
    row10.put("NAME","Guru ka Tal");
    row10.put("ARROWIMAGE",R.drawable.arrow);
    data.add(row14);        


    }

    class ListAdapter extends BaseAdapter{

    private Context context;
    private ArrayList<HashMap<String,Object>> list;
    public ListAdapter(Context context,ArrayList<HashMap<String,Object>> list){
        this.context = context;
        this.list = list;
    }

    @Override
    public int getCount() {
        return list.size();
    }

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if(convertView == null){
            holder = new ViewHolder();
            convertView =         LayoutInflater.from(context).inflate(R.layout.row,null,false);
            holder.imgItemImage = (ImageView)    convertView.findViewById(R.id.imgItemImage);
            holder.imgItemArrow = (ImageView) convertView.findViewById(R.id.imgItemArrow);
            holder.txtItemName = (TextView) convertView.findViewById(R.id.txtItemName);
            convertView.setTag(holder);
        }else{
            holder = (ViewHolder) convertView.getTag();
        }
        holder.imgItemImage.setImageResource((Integer)list.get(position).get("IMAGE"));
        holder.imgItemArrow.setImageResource((Integer)list.get(position).get("ARROWIMAGE"));
        holder.txtItemName.setText(list.get(position).get("NAME").toString());

        return convertView;
    }

    class ViewHolder{
        ImageView imgItemImage;
        ImageView imgItemArrow;
        TextView  txtItemName;
    }
}

}

Answer 1

将第一行替换为第二行：

ArrayList<HashMap<String, Object>>();
ArrayList<HashMap<String, String>>();

还有一件事：R.drawable.arrow它不是一个字符串，它是一个整数id。

Answer 2

问题在于row11方法

中对象row14到prePareListData的创建和设置数据

你在做什么

HashMap<String,Object> row11 = new HashMap<String, Object>();
row10.put("ID",11);
row10.put("IMAGE",R.drawable.chini_ka_rauza);
row10.put("NAME","Chini ka Rauza");
row10.put("ARROWIMAGE",R.drawable.arrow);
data.add(row11);

您正在创建对象row11，但未在其中设置任何值并将其添加到data。所以当getView调用

时

holder.txtItemName.setText(list.get(position).get("NAME").toString());

list.get(position).get("NAME")基本上是null，您试图在toString

上致电null String

所以你得到NullPointerException

更改

HashMap<String,Object> row11 = new HashMap<String, Object>();
row10.put("ID",11);
row10.put("IMAGE",R.drawable.chini_ka_rauza);
row10.put("NAME","Chini ka Rauza");
row10.put("ARROWIMAGE",R.drawable.arrow);
data.add(row11);

到

HashMap<String,Object> row11 = new HashMap<String, Object>();
row11.put("ID",11);
row11.put("IMAGE",R.drawable.chini_ka_rauza);
row11.put("NAME","Chini ka Rauza");
row11.put("ARROWIMAGE",R.drawable.arrow);
data.add(row11);

并对 row12 执行相同操作 row14

Android ListView显示强制关闭

2 个答案: