ImageView设置图片setBackgroundResource报空指针异常

zhanghw0212 2015-02-27 11:05:15

代码如下：



package com.example.mylistview4;





import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;







import android.app.Activity;

import android.app.AlertDialog;

import android.app.ListActivity;

import android.content.Context;

import android.content.DialogInterface;

import android.graphics.Bitmap;

import android.graphics.BitmapFactory;

import android.os.Bundle;

import android.util.Log;

import android.view.LayoutInflater;

import android.view.Menu;

import android.view.MenuItem;

import android.view.View;

import android.view.View.OnClickListener;

import android.view.ViewGroup;

import android.widget.BaseAdapter;

import android.widget.Button;

import android.widget.ImageView;

import android.widget.ListView;

import android.widget.TextView;



public class MainActivity extends ListActivity {

	

	private List<Map<String,Object>> mData;



	@Override

	protected void onCreate(Bundle savedInstanceState) {

		super.onCreate(savedInstanceState);

		mData = this.getData();

		MyAdapter adapter  = new MyAdapter(this);

		this.setListAdapter(adapter);

//		setContentView(R.layout.activity_main);

	}

	

	



	@Override

	protected void onListItemClick(ListView l, View v, int position, long id) {

		// TODO Auto-generated method stub

		Log.v("MyListView4-click", (String)mData.get(position).get("title"));

		

	}







	private List<Map<String, Object>> getData() {

		// TODO Auto-generated method stub

		 List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();

		 Map<String,Object> map = new HashMap<String,Object>();

		 map.put("title", "G1");

		 map.put("info", "google 2");

		 map.put("img", R.drawable.a2);

		 list.add(map);

		 

		 map = new HashMap<String,Object>();

		 map.put("title", "G2");

		 map.put("info", "google 3");

		 map.put("img", R.drawable.a3);

		 list.add(map);

		 

		 map = new HashMap<String,Object>();

		 map.put("title", "G3");

		 map.put("info", "google 4");

		 map.put("img", R.drawable.a1);

		 list.add(map);

		return list;

	}



	public class MyAdapter extends BaseAdapter{

		

		private LayoutInflater mInflater;

		

		public MyAdapter (Context context){

			this.mInflater = LayoutInflater.from(context);

		}



		@Override

		public int getCount() {

			// TODO Auto-generated method stub

			return mData.size();

		}



		@Override

		public Object getItem(int position) {

			// TODO Auto-generated method stub

			return null;

		}



		@Override

		public long getItemId(int position) {

			// TODO Auto-generated method stub

			return 0;

		}



		@Override

		public View getView(int position, View convertView, ViewGroup parent) {

			// TODO Auto-generated method stub

			ViewHolder holder = null;

			if(convertView == null){

				holder = new ViewHolder();

				convertView = mInflater.inflate(R.layout.activity_main, null);

				holder.img = (ImageView) convertView.findViewById(R.id.image);

				holder.title = (TextView) convertView.findViewById(R.id.title);

				holder.info = (TextView) convertView.findViewById(R.id.info);

				holder.viewBtn = (Button) convertView.findViewById(R.id.view_btn);

				convertView.setTag(holder);

				

			}else{

				holder = (ViewHolder) convertView.getTag(); 

			}

//			Integer img = (Integer) mData.get(position).get("img");

//			Bitmap  tmp=BitmapFactory.decodeResource(this.g,img)

//			

//			ImageView img = (ImageView)mData.get(position).get("img");

//			

//			holder.img.setImageBitmap(img.get );  

			holder.img.setBackgroundResource((Integer) mData.get(position).get("img"));

//			holder.img.setBackgroundResource(img);

			holder.title.setText((String) mData.get(position).get("title"));

			holder.info.setText((String) mData.get(position).get("info"));

			

			holder.viewBtn.setOnClickListener( new OnClickListener() {

				

				@Override

				public void onClick(View v) {

					// TODO Auto-generated method stub

					showInfo();

				}



				

			});

			return convertView;

		}

		

	}

	public  void showInfo() {

		// TODO Auto-generated method stub

		new AlertDialog.Builder(this)

		.setTitle("我的listView").setMessage("介绍....")

		.setPositiveButton("确定", new DialogInterface.OnClickListener() {



			@Override

			public void onClick(DialogInterface dialog, int which) {

				// TODO Auto-generated method stub

				

			}

			

		

		}).show();

	}

	

	public final class ViewHolder{

		public ImageView img;

		public TextView title;

		public TextView info;

		public Button viewBtn;

	}

}

代码运行到 holder.img.setBackgroundResource((Integer) mData.get(position).get("img")); 时就报空指针异常，本人刚刚接触Android，请各位前辈帮忙看看是什么原因，最好能给点说明建议。
感激不尽

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triplesky001 2015-02-27

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引用 3 楼 inquisitive_plus 的回复:

[quote=引用 2 楼 lulong1985 的回复:] 你确定你的资源里面有id是(Integer) mData.get(position).get("img")的图片，上面的同学说的空指针应该在holder.img = (ImageView) convertView.findViewById(R.id.image);就爆了吧

为啥会报？ convertView不为空就不会报错和image在不在都没关系，但R.id.image不在R.layout.activity_main的话得到的holder.img依然是空[/quote] 恩，是这个理，那就是赋值的时候报的

windfury_plus 2015-02-27

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引用 2 楼 lulong1985 的回复:

你确定你的资源里面有id是(Integer) mData.get(position).get("img")的图片，上面的同学说的空指针应该在holder.img = (ImageView) convertView.findViewById(R.id.image);就爆了吧

为啥会报？ convertView不为空就不会报错和image在不在都没关系，但R.id.image不在R.layout.activity_main的话得到的holder.img依然是空

triplesky001 2015-02-27

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你确定你的资源里面有id是(Integer) mData.get(position).get("img")的图片，上面的同学说的空指针应该在holder.img = (ImageView) convertView.findViewById(R.id.image);就爆了吧

windfury_plus 2015-02-27

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convertView = mInflater.inflate(R.layout.activity_main, null); holder.img = (ImageView) convertView.findViewById(R.id.image); R.id.image是不是在布局文件activity_main里不再的话holder.img会为空