Android更新UI多线程示例—五秒倒计时

Android UI 中提供invalidate()来更新界面，而invalidate()方法是非线程安全，所以需要借助handler实现。

main.xml：

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
	android:id="@+id/sv2"
	android:layout_width="fill_parent" 
	android:layout_height="fill_parent" >
	<LinearLayout 
	    android:orientation="vertical"
	    android:layout_width="fill_parent"
	    android:layout_height="fill_parent"
	    android:background="#48000000" >
		<TextView  
			android:id="@+id/number"
		    android:layout_width="fill_parent" 
		    android:layout_height="wrap_content" 
		    android:textSize="360px"
			android:textColor="#ffffff"
			android:gravity="center"
			android:paddingTop="180px" />
	</LinearLayout>
</ScrollView>

Test.java：

package com.ucrobotics.test;
 
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.view.WindowManager;
import android.widget.ScrollView;
import android.widget.TextView;
 
public class Test extends Activity {
	private ScrollView sv2;
	private TextView number;
 
	private  CountThread countThread = null;
	private Handler handler=null; 
	private int Count_Num = 5;
 
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN);
 
        try {
        	number = (TextView) findViewById(R.id.number);
 
			sv2 = (ScrollView) findViewById(R.id.sv2); 
			sv2.setFillViewport(true); //让子元素填充
 
			sv2.setBackgroundColor(Color.GREEN);
 
			handler = new Handler();
			countThread = new CountThread();
			countThread.start();
 
		} catch (Exception e) {
			e.printStackTrace();
		}
    }
 
 
    private class CountThread extends Thread{
        public void run()
        {
            while(Count_Num > 0) {
            	handler.post(runnableUi);
    			try {
    				Thread.sleep(1000);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
            }
        }
    }
 
    // 构建Runnable对象，在runnable中更新界面  
    Runnable runnableUi = new  Runnable(){
        @Override  
        public void run() {  
        	number.setText(Count_Num+"");
        	Count_Num--;
        }  
    };  
}

通过示例可以看出，Layout的更新请求需要通过：handler.post(runnableUi) 发送过去。
运行效果就是启动后，屏幕数字从5倒计时到1...