Android 的消息机制（3）-优快云博客

本文介绍如何在Android中通过隐式方式指定Looper来创建Handler对象，从而实现与主线程MessageQueue的交互。通过实例代码展示了创建EventHandler对象的过程及其如何用于更新UI。

当然我们也可以隐式的指定Looper ，代码如下：

^?[Copy to clipboard] Download zuiniuwang.java

/**
* MessageQueue2.java
* com.test
*
* Function： TODO
*
* ver date author
* ──────────────────────────────────
* 2011-3-20 Leon
*
*/
package com.test.messagequeue;
/**
* ClassName:MessageQueue2
* Function: TODO ADD FUNCTION
* Reason: TODO ADD REASON
*
* @author Leon
* @version
* @since Ver 1.1
* @Date 2011-3-20
*/
import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;
public class MessageQueue3 extends Activity implements OnClickListener {
private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT;
private final int FP = LinearLayout.LayoutParams.FILL_PARENT;
public TextView tv;
private myThread t;
private Button btn, btn2, btn3;
private EHandler mHandler;
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
LinearLayout layout = new LinearLayout(this);
layout.setOrientation(LinearLayout.VERTICAL);
btn = new Button(this);
btn.setId(101);
btn.setText("test looper");
btn.setOnClickListener(this);
LinearLayout.LayoutParams param =
new LinearLayout.LayoutParams(100,50);
param.topMargin = 10;
layout.addView(btn, param);
btn2 = new Button(this);
btn2.setId(102);
btn2.setText("exit");
btn2.setOnClickListener(this);
layout.addView(btn2, param);
tv = new TextView(this);
tv.setTextColor(Color.WHITE);
tv.setText("");
LinearLayout.LayoutParams param2 =
new LinearLayout.LayoutParams(FP, WC);
param2.topMargin = 10;
layout.addView(tv, param2);
setContentView(layout);
}
public void onClick(View v) {
switch(v.getId()){
case 101:
// mHandler = new EHandler(Looper.myLooper());
//可以隐式的制定Looper,和上面的效果是一样的
mHandler = new EHandler();
t = new myThread();
t.start();
break;
case 102:
finish();
break;
}
}
//------------------------------------------------------
class EHandler extends Handler {
public EHandler(Looper looper) {
super(looper);
}
public EHandler(){
}
@Override
public void handleMessage(Message msg) {
tv.setText((String)msg.obj);
}
}
//------------------------------------------------------
class myThread extends Thread{
public void run() {
String obj = "This message is from new thread.";
mHandler.removeMessages(0);
Message m = mHandler.obtainMessage(1, 1, 1, obj);
mHandler.sendMessage(m);
}
}

在此代码中，指令：h = new EventHandler()；就等于：h = new EventHandler(Looper.myLooper())；
它建立了当前线程(Current Thread)的EventHandler对象。由于是由main线程执行此指令的，所以此EventHandler对象是用来存取main线程的Message Queue的。

本文转自最牛傻蛋 51CTO博客，原文链接：http://blog.51cto.com/zuiniuwang/718338，如需转载请自行联系原作者