android 定时器，每秒变换一次图片！

在android中，要让每秒进行一次ui更新，就需要利用到定时器和handler，message的结合，如果不使用handler就不能达到更新ui的效果，我的理解是handler中存在一个队列问题，可以保证不产生阻塞。

代码如下：

package com.my;

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.widget.ImageView;
import android.widget.LinearLayout;

public class MainActivity extends Activity
{
private LinearLayout linearlayout;

private ImageView main_imageview;

private int i = 0;

Timer timer = new Timer();

private Handler handler = new Handler()
{
@Override
public void handleMessage(Message msg)
{

Log.e("@@@", i + "");
//index=msg.what;
if (i > 6)
{
i = 0;
}
else
{
switch (i)
{
case 1:
main_imageview.setImageResource(R.drawable.loader_frame_1);
break;
case 2:
main_imageview.setImageResource(R.drawable.loader_frame_2);
break;
case 3:
main_imageview.setImageResource(R.drawable.loader_frame_3);
break;
case 4:
main_imageview.setImageResource(R.drawable.loader_frame_4);
break;
case 5:
main_imageview.setImageResource(R.drawable.loader_frame_5);
break;
case 6:
main_imageview.setImageResource(R.drawable.loader_frame_6);
break;
default:
break;
}
linearlayout.invalidate();
}
super.handleMessage(msg);
}
};

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

initView();
}

public void initView()
{
linearlayout = (LinearLayout) findViewById(R.id.background_main);
main_imageview = (ImageView) findViewById(R.id.main_imageview);

timer.scheduleAtFixedRate(new TimerTask()
{
@Override
public void run()
{
// TODO Auto-generated method stub
i++;
Message mesasge = new Message();
mesasge.what = i;
handler.sendMessage(mesasge);
}
}, 0, 500);
}

@Override
protected void onDestroy()
{
// TODO Auto-generated method stub
timer.cancel();
super.onDestroy();
}
}

在这段代码中有两点需要注意：

第一：在更新完图片后，需要刷新整个布局，linearlayout.invalidate();

第二：在用完定时器timer后，要在Activity被干掉的同时销毁定时器timer。