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。