Android ListView NullPointerException

[youxunlong]

我想要创建一个ListView显示Android系统中所有的APP
下面是正确的代码(已验证)

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			ViewHolder holder;
			if(convertView==null){
				holder = new ViewHolder();
				convertView = View.inflate(context, R.layout.item_app, null);
				holder.drawable = (ImageView) convertView.findViewById(R.id.iv_app);
				holder.name = (TextView) convertView.findViewById(R.id.tv_appName);
				holder.isRom = (TextView) convertView.findViewById(R.id.tv_isRom);
				holder.size = (TextView) convertView.findViewById(R.id.tv_appSize);
				convertView.setTag(holder);
			}else{
				holder = (ViewHolder) convertView.getTag();
			}
			
			AppInfo appInfo = null;
			//line4
	//		if(position==userList.size()){
	//			TextView tv = new TextView(context);
	//			tv.setText("系统jjjjjjjjjjjjjjjjjjjjjjjjj");
	//			return tv;
	//		}
			if(position>=0 && position<userList.size()){
				appInfo = userList.get(position);
				//exchange line2
	//		}else if(position>userList.size() && position<getCount()){
			}else if(position>=userList.size() && position<getCount()){
				//exchange line3
	//			appInfo = systemList.get(position-userList.size()-1);
				appInfo = systemList.get(position-userList.size());
			}
			holder.drawable.setImageDrawable(appInfo.icon);
			holder.name.setText(appInfo.appName);
			if(appInfo.isInRom){
				holder.isRom.setText("手机内存");
			}else{
				holder.isRom.setText("SD卡内存");
			}
			String size = Formatter.formatFileSize(context, appInfo.appSize);
			holder.size.setText(size);
			
			
			return convertView;
		}
		
		class ViewHolder{
			ImageView drawable;
			TextView name;
			TextView isRom;
			TextView size;
		}

运行结果如下

然后我换了line1,line2,line3,取消注释line4，实现代码如下：

@Override
	public View getView(int position, View convertView, ViewGroup parent) {
		ViewHolder holder;
		if(convertView==null){
			holder = new ViewHolder();
			convertView = View.inflate(context, R.layout.item_app, null);
			holder.drawable = (ImageView) convertView.findViewById(R.id.iv_app);
			holder.name = (TextView) convertView.findViewById(R.id.tv_appName);
			holder.isRom = (TextView) convertView.findViewById(R.id.tv_isRom);
			holder.size = (TextView) convertView.findViewById(R.id.tv_appSize);
			convertView.setTag(holder);
		}else{
			holder = (ViewHolder) convertView.getTag();
		}
		
		AppInfo appInfo = null;
		//line4
		if(position==userList.size()){
			TextView tv = new TextView(context);
			tv.setText("系统jjjjjjjjjjjjjjjjjjjjjjjjj");
			return tv;
		}
		if(position>=0 && position<userList.size()){
			appInfo = userList.get(position);
			//exchange line2
		}else if(position>userList.size() && position<getCount()){
	//		}else if(position>=userList.size() && position<getCount()){
			//exchange line3
			appInfo = systemList.get(position-userList.size()-1);
	//			appInfo = systemList.get(position-userList.size());
		}
		holder.drawable.setImageDrawable(appInfo.icon);
		holder.name.setText(appInfo.appName);
		if(appInfo.isInRom){
			holder.isRom.setText("手机内存");
		}else{
			holder.isRom.setText("SD卡内存");
		}
		String size = Formatter.formatFileSize(context, appInfo.appSize);
		holder.size.setText(size);
		
		
		return convertView;
	}
	
	class ViewHolder{
		ImageView drawable;
		TextView name;
		TextView isRom;
		TextView size;
	}

运行结果如下，ListView中有一个TextView对象

程序运行了，然后我滑动ListView,当TExtView消失时，软件就奔溃了

01-11 09:46:41.046: D/AndroidRuntime(6132): Shutting down VM
	01-11 09:46:41.046: W/dalvikvm(6132): threadid=1: thread exiting with uncaught exception (group=0xa4ce2b20)
	01-11 09:46:41.046: E/AndroidRuntime(6132): FATAL EXCEPTION: main
	01-11 09:46:41.046: E/AndroidRuntime(6132): Process: com.xunlong.softwaremanagermodule, PID: 6132
	01-11 09:46:41.046: E/AndroidRuntime(6132): java.lang.NullPointerException
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at com.xunlong.softwaremanagermodule.AppAdapter.getView(AppAdapter.java:77)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.AbsListView.obtainView(AbsListView.java:2255)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.ListView.makeAndAddView(ListView.java:1790)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.ListView.fillDown(ListView.java:691)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.ListView.fillGap(ListView.java:655)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.AbsListView.trackMotionScroll(AbsListView.java:5143)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.AbsListView.scrollIfNeeded(AbsListView.java:3243)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.AbsListView.onTouchMove(AbsListView.java:3587)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.widget.AbsListView.onTouchEvent(AbsListView.java:3431)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.view.View.dispatchTouchEvent(View.java:7706)
	01-11 09:46:41.046: E/AndroidRuntime(6132): 	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2210)

[YXTS122]

把TextView声明为全局变量看看怎么样。。

[寒冰大神]

错误在 77 行啊，77行是哪行？， 你getCount() 是多少？

[寒冰大神]

把 if(position==userList.size()){ TextView tv = new TextView(context); tv.setText("系统jjjjjjjjjjjjjjjjjjjjjjjjj"); return tv; } 放到 if(convertView==null){ 前面 试试。