Android 的消息机制（4）
上面的文章我们演示了如何把一个Message由子线程发送给主线程，但是如何将一个Message从主线程发送给子线程呢？子线程在默认的情况下是没有Looper的，也就没有可能操作子线程的消息队列。我们通过查API文档可以看到： Class used to run a message loop for a thread. Threads by default do not have a message loop associated with them; to create one, call prepare() in the thread that is to run the loop, and then loop() to have it process messages until the loop is stopped. Most interaction with a message loop is through the Handler class. 大概意思是，线程在默认情况下是没有Looper的，但是可以通过调用Prepare()方法来运行一个loop，然后使用loop()方法来处理消息直到loop结束。通常的使用方式是： ?[Copy to clipboard] Downloadzuiniuwang.java classLooperThreadextendsThread{ publicHandlermHandler; publicvoidrun(){ Looper.prepare(); mHandler=newHandler(){ publicvoidhandleMessage(Messagemsg){//processincoming //messageshere } }; Looper.loop(); } } 例程如下，基本过程是这样的，启动主线程，然后启动子线程，子线程注册Looper，主线程发送一个Message给子线程，然后子线程的handler处理此消息，再把此消息发送给主线程的消息队列，主线程空间显示此消息~ ?[Copy to clipboard] Downloadzuiniuwang.java /** *MessageExample4.java *com.test.Message * *Function：TODO * *verdateauthor *────────────────────────────────── *2011-3-23Leon * *Copyright(c)2011,TNTAllRightsReserved. */ packagecom.test.Message; importandroid.app.Activity; importandroid.graphics.Color; importandroid.os.Bundle; importandroid.os.Handler; importandroid.os.Looper; importandroid.os.Message; importandroid.view.View; importandroid.view.View.OnClickListener; importandroid.widget.Button; importandroid.widget.LinearLayout; importandroid.widget.TextView; /** *ClassName:MessageExample4主线程如何传递消息给子线程Function:TODOADDFUNCTIONReason: *TODOADDREASON * *@authorLeon *@version *@sinceVer1.1 *@Date2011-3-23 */ publicclassMessageExample4extendsActivityimplementsOnClickListener{ privatefinalintWC=LinearLayout.LayoutParams.WRAP_CONTENT; privatefinalintFP=LinearLayout.LayoutParams.FILL_PARENT; publicTextViewtv; privateButtonbtn,btn2; privateHandlerh; publicvoidonCreate(Bundleicicle){ super.onCreate(icicle); LinearLayoutlayout=newLinearLayout(this); layout.setOrientation(LinearLayout.VERTICAL); btn=newButton(this); btn.setId(101); btn.setText("testlooper"); btn.setOnClickListener(this); LinearLayout.LayoutParamsparam=newLinearLayout.LayoutParams(100,50); param.topMargin=10; layout.addView(btn,param); btn2=newButton(this); btn2.setId(102); btn2.setText("exit"); btn2.setOnClickListener(this); layout.addView(btn2,param); tv=newTextView(this); tv.setTextColor(Color.WHITE); tv.setText(""); LinearLayout.LayoutParamsparam2=newLinearLayout.LayoutParams(FP,WC); param2.topMargin=10; layout.addView(tv,param2); setContentView(layout); //启动子线程 newmyThread().start(); } publicvoidonClick(Viewv){ switch(v.getId()){ case101: Stringobj="mainThread"; Messagem=h.obtainMessage(1,1,1,obj); h.sendMessage(m); break; case102: finish(); break; } } //------------------------------------------------------ classEHandlerextendsHandler{ publicEHandler(Looperlooper){ super(looper); } @Override publicvoidhandleMessage(Messagemsg){ tv.setText((String)msg.obj); } } //------------------------------------------------------ classmyThreadextendsThread{ privateEHandlermHandler; publicvoidrun(){ Looper.prepare(); h=newHandler(){ publicvoidhandleMessage(Messagemsg){ EHandlerha=newEHandler(Looper.getMainLooper()); Stringobj=(String)msg.obj+",myThread"; Messagem=ha.obtainMessage(1,1,1,obj); ha.sendMessage(m); } }; Looper.loop(); } } } 本文转自 最牛傻蛋 51CTO博客，原文链接：http://blog.51cto.com/zuiniuwang/718336，如需转载请自行联系原作者
