關於ListView的getView方法被多次重複呼叫的問題

package com.pxy.demo.adapter;

import java.util.ArrayList;

import com.pxy.demo.R;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;

public class MyAdapter extends BaseAdapter{

	private ArrayList<String> list;
	private Context context;
	
	public MyAdapter(Context context,ArrayList<String> list) {
		super();
		this.context = context;
		this.list = list;
	}

	@Override
	public int getCount() {
		return list == null? 0 :list.size();
	}

	@Override
	public Object getItem(int position) {
		return null;
	}

	@Override
	public long getItemId(int position) {
		return 0;
	}

	@Override
	public View getView(int position, View v, ViewGroup parent) {
		ViewHolder holder = null;
		System.out.println("view = "+v + "  position = " + position);
			if(v == null){
				System.out.println("view = null 時進入方法");
				holder = new ViewHolder();
				v = LayoutInflater.from(context).inflate(R.layout.item, null);
				holder.mButton = (Button) v.findViewById(R.id.btn);
				v.setTag(holder);
			}else{
				holder = (ViewHolder) v.getTag();
		}
		String str = list.get(position);
		if(str!=null){
			holder.mButton.setText(str);
		}
		return v;
	}
	
	private class ViewHolder {
       Button mButton;
	}

}