Adapter extends ArrayAdapter 的片段代码

<span style="font-family: Arial, Helvetica, sans-serif;"></span><pre name="code" class="java">public class MsgAdapter extends ArrayAdapter<Msg> {
	private int resourceId;
	
	public MsgAdapter(Context context,int textViewResourceId,List<Msg> objects){
		super(context, textViewResourceId, objects);
		resourceId = textViewResourceId;
	}
	
	@Override
	public View getView(int position, View convertView,ViewGroup parent){
		//Log.d("问题","getView " + position + " " + convertView);
		Msg msg = getItem(position);
		View view;
		ViewHolder viewHolder;
		if(convertView == null){
			view = LayoutInflater.from(getContext()).inflate(resourceId,null);
			viewHolder = new ViewHolder();
			viewHolder.leftLayout = (LinearLayout) view.findViewById(R.id.left_layout);
			viewHolder.rightLayout = (LinearLayout) view.findViewById(R.id.right_layout);
			viewHolder.leftMsg = (TextView)view.findViewById(R.id.left_msg);
			viewHolder.rightMsg = (TextView)view.findViewById(R.id.right_msg);
			view.setTag(viewHolder);
			
		}else{
			view = convertView;
			viewHolder = (ViewHolder) view.getTag();
		}
		
		
		if(msg.getType() == Msg.TYPE_RECEIVED){
			//如果是收到的消息，则显示左边的消息布局，将右边的消息布局隐藏。
			viewHolder.leftLayout.setVisibility(View.VISIBLE);
			viewHolder.rightLayout.setVisibility(View.GONE);
			viewHolder.leftMsg.setText(msg.getContent());
		}else if(msg.getType() == Msg.TYPE_SENT){
			//如果是发出的消息，则显示右边的消息布局，将左边的消息布局隐藏
			viewHolder.rightLayout.setVisibility(View.VISIBLE);
			viewHolder.leftLayout.setVisibility(View.GONE);//如果不设置则会出现两边显示的情况。即收到自己发出的信息。
			viewHolder.rightMsg.setText(msg.getContent());
		}
		return view;
		
	}

<span style="font-family: Arial, Helvetica, sans-serif;">Msg msg = getItem(position);</span>

这个函数接收的是从不可视区域进入可视区域的实例。（即listview上要显示的元素项）

<pre name="code" class="java">View convertView 这个值为安卓系统自动为我们缓存的之前加载的布局？

view.setTag(viewHolder);这个函数将我们的viewHolder打包进行保存进View中，这个view不知道怎么工作的。。。。