Android的消息机制(4)
2011-12-30 11:50 tang768168 阅读(181) 评论(0) 编辑 收藏 举报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:
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class LooperThread extends Thread { public Handler mHandler; public void run() { Looper.prepare(); mHandler = new Handler() { public void handleMessage(Message msg) { // process incoming // messages here } }; 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~
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/** * MessageExample4.java * com.test.Message * * Function: TODO * * ver date author * ────────────────────────────────── * 2011-3-23 Leon * * Copyright (c) 2011, TNT All Rights Reserved. */ package com.test.Message; 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; /** * ClassName:MessageExample4 主线程如何传递消息给子线程 Function: TODO ADD FUNCTION Reason: * TODO ADD REASON * * @author Leon * @version * @since Ver 1.1 * @Date 2011-3-23 */ public class MessageExample4 extends Activity implements OnClickListener { private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT; private final int FP = LinearLayout.LayoutParams.FILL_PARENT; public TextView tv; private Button btn, btn2; private Handler h; 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); // 启动子线程 new myThread().start(); } public void onClick(View v) { switch (v.getId()) { case 101: String obj = "mainThread"; Message m = h.obtainMessage(1, 1, 1, obj); h.sendMessage(m); break; case 102: finish(); break; } } // ------------------------------------------------------ class EHandler extends Handler { public EHandler(Looper looper) { super(looper); } @Override public void handleMessage(Message msg) { tv.setText((String) msg.obj); } } // ------------------------------------------------------ class myThread extends Thread { private EHandler mHandler; public void run() { Looper.prepare(); h = new Handler() { public void handleMessage(Message msg) { EHandler ha = new EHandler(Looper.getMainLooper()); String obj = (String) msg.obj + ", myThread"; Message m = ha.obtainMessage(1, 1, 1, obj); ha.sendMessage(m); } }; Looper.loop(); } } } |
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