1.活用Android线程间通信的Message机制 1.1.Message 代码在frameworks\base\core\java\android\Os\Message.java中。 Message.obtain函数：有多个obtain函数，主要功能一样，只是参数不一样。作用是从Message Pool中取出一个Message，如果Message Pool中已经没有Message可取则新建一个Message返回，同时用对应的参数给得到的Message对象赋值。 Message Pool：大小为10个；通过Message.mPool->（Message并且Message.next）-> （Message并且Message.next）-> （Message并且Message.next）...构造一个Message Pool。Message Pool的第一个元素直接new出来，然后把Message.mPool（static类的static变量）指向它。其他的元素都是使用完的 Message通过Message的recycle函数清理后放到Message Pool（通过Message Pool最后一个Message的next指向需要回收的Message的方式实现）。下图为Message Pool的结构： 
1.2.MessageQueue MessageQueue里面有一个收到的Message的对列： MessageQueue.mMessages(static变量)->( Message并且Message.next)-> ( Message并且Message.next)->...，下图为接收消息的消息队列： 
上层代码通过Handler的sendMessage等函数放入一个message到MessageQueue里面时最终会调用 MessageQueue的 enqueueMessage函数。enqueueMessage根据上面的接收的Message的队列的构造把接收到的Message放入队列中。 MessageQueue的removeMessages函数根据上面的接收的Message的队列的构造把接收到的Message从队列中删除，并且调用对应Message对象的recycle函数把不用的Message放入Message Pool中。 1.3.Looper Looper对象的创建是通过prepare函数，而且每一个Looper对象会和一个线程关联 Java代码
1 public static final void prepare() {
2 if (sThreadLocal.get() != null) {
3 throw new RuntimeException("Only one Looper may be created per thread");
4 }
5 sThreadLocal.set(new Looper());
6 }
public static final void prepare() { if (sThreadLocal.get() != null) { throw new RuntimeException("Only one Looper may be created per thread"); } sThreadLocal.set(new Looper()); } Looper对象创建时会创建一个MessageQueue，主线程默认会创建一个Looper从而有MessageQueue，其他线程默认是 没有 MessageQueue的不能接收Message，如果需要接收Message则需要通过prepare函数创建一个MessageQueue。具体操 作请见示例代码。 Java代码
1 private Looper() {
2 mQueue = new MessageQueue();
3 mRun = true;
4 mThread = Thread.currentThread();
5 }
private Looper() { mQueue = new MessageQueue(); mRun = true; mThread = Thread.currentThread(); } prepareMainLooper函数只给主线程调用（系统处理，程序员不用处理），它会调用prepare建立Looper对象和MessageQueue。 Java代码
public static final void prepareMainLooper() { prepare(); setMainLooper(myLooper()); if (Process.supportsProcesses()) { myLooper().mQueue.mQuitAllowed = false; } } 1 public static final void prepareMainLooper() {
2 prepare();
3 setMainLooper(myLooper());
4 if (Process.supportsProcesses()) {
5 myLooper().mQueue.mQuitAllowed = false;
6 }
7 }
Loop函数从MessageQueue中从前往后取出Message，然后通过Handler的dispatchMessage函数进行消息的 处理（可见消息的处理是Handler负责的），消息处理完了以后通过Message对象的recycle函数放到Message Pool中，以便下次使用，通过Pool的处理提供了一定的内存管理从而加速消息对象的获取。至于需要定时处理的消息如何做到定时处理，请见 MessageQueue的next函数，它在取Message来进行处理时通过判断MessageQueue里面的Message是否符合时间要求来决 定是否需要把Message取出来做处理，通过这种方式做到消息的定时处理。 Java代码
1 public static final void loop() {
2 Looper me = myLooper();
3 MessageQueue queue = me.mQueue;
4 while (true) {
5 Message msg = queue.next(); // might block
6 //if (!me.mRun) {
7 // break;
8 //}
9 if (msg != null) {
10 if (msg.target == null) {
11 // No target is a magic identifier for the quit message
12 return;
13 }
14
15 if (me.mLogging!= null)
16 me.mLogging.println(">>>>> Dispatching to " + msg.target + " "+ msg.callback + ": " + msg.what);
17 msg.target.dispatchMessage(msg);
18 if (me.mLogging!= null)
19 me.mLogging.println("<<<<< Finished to" + msg.target + " "+ msg.callback);
20 msg.recycle();
21 }
22 }
23 }
Java代码
1 public Handler(Looper looper, Callback callback) {
2 mLooper = looper;
3 mQueue = looper.mQueue;
4 mCallback = callback;
5 }
6
7 public interface Callback {
8 public boolean handleMessage(Message msg);
9 }
public Handler(Looper looper, Callback callback) { mLooper = looper; mQueue = looper.mQueue; mCallback = callback; } public interface Callback { public boolean handleMessage(Message msg); } 获取消息：直接通过Message的obtain方法获取一个Message对象。 Java代码
1 public final Message obtainMessage(int what, int arg1, int arg2, Object obj){
2 return Message.obtain(this, what, arg1, arg2, obj);
3 }
public final Message obtainMessage(int what, int arg1, int arg2, Object obj){ return Message.obtain(this, what, arg1, arg2, obj); } 发送消息：通过MessageQueue的enqueueMessage把Message对象放到MessageQueue的接收消息队列中 Java代码
public boolean sendMessageAtTime(Message msg, long uptimeMillis){ boolean sent = false; MessageQueue queue = mQueue; if (queue != null) { msg.target = this; sent = queue.enqueueMessage(msg, uptimeMillis); } else { RuntimeException e = new RuntimeException(this + " sendMessageAtTime() called with no mQueue"); Log.w("Looper", e.getMessage(), e); } return sent; } 1 public boolean sendMessageAtTime(Message msg, long uptimeMillis){
2 boolean sent = false;
3 MessageQueue queue = mQueue;
4 if (queue != null) {
5 msg.target = this;
6 sent = queue.enqueueMessage(msg, uptimeMillis);
7 } else {
8 RuntimeException e = new RuntimeException(this + " sendMessageAtTime() called with no mQueue");
9 Log.w("Looper", e.getMessage(), e);
10 }
11 return sent;
12 }
线程如何处理MessageQueue中接收的消息：在Looper的loop函数中循环取出MessageQueue的接收消息队列中的消息， 然后调用 Hander的dispatchMessage函数对消息进行处理，至于如何处理（相应消息）则由用户指定（三个方法，优先级从高到低：Message里 面的Callback，一个实现了Runnable接口的对象，其中run函数做处理工作；Handler里面的mCallback指向的一个实现了 Callback接口的对象，里面的handleMessage进行处理；处理消息Handler对象对应的类继承并实现了其中 handleMessage函数，通过这个实现的handleMessage函数处理消息）。 Java代码
1 public void dispatchMessage(Message msg) {
2 if (msg.callback != null) {
3 handleCallback(msg);
4 } else {
5 if (mCallback != null) {
6 if (mCallback.handleMessage(msg)) {
7 return;
8 }
9 }
10 handleMessage(msg);
11 }
12 }
public void dispatchMessage(Message msg) { if (msg.callback != null) { handleCallback(msg); } else { if (mCallback != null) { if (mCallback.handleMessage(msg)) { return; } } handleMessage(msg); } } Runnable说明：Runnable只是一个接口，实现了这个接口的类对应的对象也只是个普通的对象，并不是一个Java中的Thread。Thread类经常使用Runnable，很多人有误解，所以这里澄清一下。 从上可知以下关系图： 
其中清理Message是Looper里面的loop函数指把处理过的Message放到Message的Pool里面去，如果里面已经超过最大值10个，则丢弃这个Message对象。 调用Handler是指Looper里面的loop函数从MessageQueue的接收消息队列里面取出消息，然后根据消息指向的Handler对象调用其对应的处理方法。 1.5.代码示例 下面我们会以android实例来展示对应的功能，程序界面于下： 
程序代码如下，后面部分有代码说明： Java代码
1 package com.android.messageexample;
2 import android.app.Activity;
3 import android.content.Context;
4 import android.graphics.Color;
5 import android.os.Bundle;
6 import android.os.Handler;
7 import android.os.Looper;
8 import android.os.Message;
9 import android.util.Log;
10 import android.view.View;
11 import android.view.View.OnClickListener;
12 import android.widget.Button;
13 import android.widget.LinearLayout;
14 import android.widget.TextView;
15 public class MessageExample extends Activity implements OnClickListener {
16 private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT;
17 private final int FP = LinearLayout.LayoutParams.FILL_PARENT;
18 public TextView tv;
19 private EventHandler mHandler;
20 private Handler mOtherThreadHandler=null;
21 private Button btn, btn2, btn3, btn4, btn5, btn6;
22 private NoLooperThread noLooerThread = null;
23 private OwnLooperThread ownLooperThread = null;
24 private ReceiveMessageThread receiveMessageThread =null;
25 private Context context = null;
26 private final String sTag = "MessageExample";
27 private boolean postRunnable = false;
28
29 /** Called when the activity is first created. */
30 @Override
31 public void onCreate(Bundle savedInstanceState) {
32 super.onCreate(savedInstanceState);
33 context = this.getApplicationContext();
34 LinearLayout layout = new LinearLayout(this);
35 layout.setOrientation(LinearLayout.VERTICAL);
36 btn = new Button(this);
37 btn.setId(101);
38 btn.setText("message from main thread self");
39 btn.setOnClickListener(this);
40 LinearLayout.LayoutParams param =
41 new LinearLayout.LayoutParams(250,50);
42 param.topMargin = 10;
43 layout.addView(btn, param);
44 btn2 = new Button(this);
45 btn2.setId(102);
46 btn2.setText("message from other thread to main thread");
47 btn2.setOnClickListener(this);
48 layout.addView(btn2, param);
49 btn3 = new Button(this);
50 btn3.setId(103);
51 btn3.setText("message to other thread from itself");
52 btn3.setOnClickListener(this);
53 layout.addView(btn3, param);
54 btn4 = new Button(this);
55 btn4.setId(104);
56 btn4.setText("message with Runnable as callback from other thread to main thread");
57 btn4.setOnClickListener(this);
58 layout.addView(btn4, param);
59 btn5 = new Button(this);
60 btn5.setId(105);
61 btn5.setText("main thread's message to other thread");
62 btn5.setOnClickListener(this);
63 layout.addView(btn5, param);
64 btn6 = new Button(this);
65 btn6.setId(106);
66 btn6.setText("exit");
67 btn6.setOnClickListener(this);
68 layout.addView(btn6, param);
69 tv = new TextView(this);
70 tv.setTextColor(Color.WHITE);
71 tv.setText("");
72 LinearLayout.LayoutParams param2 =
73 new LinearLayout.LayoutParams(FP, WC);
74 param2.topMargin = 10;
75 layout.addView(tv, param2);
76 setContentView(layout);
77
78 //主线程要发送消息给other thread， 这里创建那个other thread
79 receiveMessageThread = new ReceiveMessageThread();
80 receiveMessageThread.start();
81 }
82
83 //implement the OnClickListener interface
84 @Override
85 public void onClick(View v) {
86 switch(v.getId()){
87 case 101:
88 //主线程发送消息给自己
89 Looper looper;
90 looper = Looper.myLooper(); //get the Main looper related with the main thread
91 //如果不给任何参数的话会用当前线程对应的Looper(这里就是Main Looper)为Handler里面的成员mLooper赋值
92 mHandler = new EventHandler(looper);
93 //mHandler = new EventHandler();
94 // 清除整个MessageQueue里的消息
95 mHandler.removeMessages(0);
96 String obj = "This main thread's message and received by itself!";
97 //得到Message对象
98 Message m = mHandler.obtainMessage(1, 1, 1, obj);
99 // 将Message对象送入到main thread的MessageQueue里面
100 mHandler.sendMessage(m);
101 break;
102 case 102:
103 //other线程发送消息给主线程
104 postRunnable = false;
105 noLooerThread = new NoLooperThread();
106 noLooerThread.start();
107 break;
108 case 103:
109 //other thread获取它自己发送的消息
110 tv.setText("please look at the error level log for other thread received message");
111 ownLooperThread = new OwnLooperThread();
112 ownLooperThread.start();
113 break;
114 case 104:
115 //other thread通过Post Runnable方式发送消息给主线程
116 postRunnable = true;
117 noLooerThread = new NoLooperThread();
118 noLooerThread.start();
119 break;
120 case 105:
121 //主线程发送消息给other thread
122 if(null!=mOtherThreadHandler){
123 tv.setText("please look at the error level log for other thread received message from main thread");
124 String msgObj = "message from mainThread";
125 Message mainThreadMsg = mOtherThreadHandler.obtainMessage(1, 1, 1, msgObj);
126 mOtherThreadHandler.sendMessage(mainThreadMsg);
127 }
128 break;
129 case 106:
130 finish();
131 break;
132 }
133 }
134 class EventHandler extends Handler
135 {
136 public EventHandler(Looper looper) {
137 super(looper);
138 }
139 public EventHandler() {
140 super();
141 }
142 public void handleMessage(Message msg) {
143 //可以根据msg.what执行不同的处理，这里没有这么做
144 switch(msg.what){
145 case 1:
146 tv.setText((String)msg.obj);
147 break;
148 case 2:
149 tv.setText((String)msg.obj);
150 noLooerThread.stop();
151 break;
152 case 3:
153 //不能在非主线程的线程里面更新UI，所以这里通过Log打印收到的消息
154 Log.e(sTag, (String)msg.obj);
155 ownLooperThread.stop();
156 break;
157 default:
158 //不能在非主线程的线程里面更新UI，所以这里通过Log打印收到的消息
159 Log.e(sTag, (String)msg.obj);
160 break;
161 }
162 }
163 }
164 //NoLooperThread
165 class NoLooperThread extends Thread{
166 private EventHandler mNoLooperThreadHandler;
167 public void run() {
168 Looper myLooper, mainLooper;
169 myLooper = Looper.myLooper();
170 mainLooper = Looper.getMainLooper(); //这是一个static函数
171 String obj;
172 if(myLooper == null){
173 mNoLooperThreadHandler = new EventHandler(mainLooper);
174 obj = "NoLooperThread has no looper and handleMessage function executed in main thread!";
175 }
176 else {
177 mNoLooperThreadHandler = new EventHandler(myLooper);
178 obj = "This is from NoLooperThread self and handleMessage function executed in NoLooperThread!";
179 }
180 mNoLooperThreadHandler.removeMessages(0);
181 if(false == postRunnable){
182 //send message to main thread
183 Message m = mNoLooperThreadHandler.obtainMessage(2, 1, 1, obj);
184 mNoLooperThreadHandler.sendMessage(m);
185 Log.e(sTag, "NoLooperThread id:" + this.getId());
186 }else{
187 //下面new出来的实现了Runnable接口的对象中run函数是在Main Thread中执行，不是在NoLooperThread中执行
188 //注意Runnable是一个接口，它里面的run函数被执行时不会再新建一个线程
189 //您可以在run上加断点然后在eclipse调试中看它在哪个线程中执行
190 mNoLooperThreadHandler.post(new Runnable(){
191 @Override
192 public void run() {
193 tv.setText("update UI through handler post runnalbe mechanism!");
194 noLooerThread.stop();
195 }
196 });
197 }
198 }
199 }
200
201 //OwnLooperThread has his own message queue by execute Looper.prepare();
202 class OwnLooperThread extends Thread{
203 private EventHandler mOwnLooperThreadHandler;
204 public void run() {
205 Looper.prepare();
206 Looper myLooper, mainLooper;
207 myLooper = Looper.myLooper();
208 mainLooper = Looper.getMainLooper(); //这是一个static函数
209 String obj;
210 if(myLooper == null){
211 mOwnLooperThreadHandler = new EventHandler(mainLooper);
212 obj = "OwnLooperThread has no looper and handleMessage function executed in main thread!";
213 }
214 else {
215 mOwnLooperThreadHandler = new EventHandler(myLooper);
216 obj = "This is from OwnLooperThread self and handleMessage function executed in NoLooperThread!";
217 }
218 mOwnLooperThreadHandler.removeMessages(0);
219 //给自己发送消息
220 Message m = mOwnLooperThreadHandler.obtainMessage(3, 1, 1, obj);
221 mOwnLooperThreadHandler.sendMessage(m);
222 Looper.loop();
223 }
224 }
225
226 //ReceiveMessageThread has his own message queue by execute Looper.prepare();
227 class ReceiveMessageThread extends Thread{
228 public void run() {
229 Looper.prepare();
230 mOtherThreadHandler = new Handler(){
231 public void handleMessage(Message msg) {
232 Log.e(sTag, (String)msg.obj);
233 }
234 };
235 Looper.loop();
236 }
237 }
238
239 }
package com.android.messageexample; import android.app.Activity; import android.content.Context; import android.graphics.Color; import android.os.Bundle; import android.os.Handler; import android.os.Looper; import android.os.Message; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.LinearLayout; import android.widget.TextView; public class MessageExample extends Activity implements OnClickListener { private final int WC = LinearLayout.LayoutParams.WRAP_CONTENT; private final int FP = LinearLayout.LayoutParams.FILL_PARENT; public TextView tv; private EventHandler mHandler; private Handler mOtherThreadHandler=null; private Button btn, btn2, btn3, btn4, btn5, btn6; private NoLooperThread noLooerThread = null; private OwnLooperThread ownLooperThread = null; private ReceiveMessageThread receiveMessageThread =null; private Context context = null; private final String sTag = "MessageExample"; private boolean postRunnable = false; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); context = this.getApplicationContext(); LinearLayout layout = new LinearLayout(this); layout.setOrientation(LinearLayout.VERTICAL); btn = new Button(this); btn.setId(101); btn.setText("message from main thread self"); btn.setOnClickListener(this); LinearLayout.LayoutParams param = new LinearLayout.LayoutParams(250,50); param.topMargin = 10; layout.addView(btn, param); btn2 = new Button(this); btn2.setId(102); btn2.setText("message from other thread to main thread"); btn2.setOnClickListener(this); layout.addView(btn2, param); btn3 = new Button(this); btn3.setId(103); btn3.setText("message to other thread from itself"); btn3.setOnClickListener(this); layout.addView(btn3, param); btn4 = new Button(this); btn4.setId(104); btn4.setText("message with Runnable as callback from other thread to main thread"); btn4.setOnClickListener(this); layout.addView(btn4, param); btn5 = new Button(this); btn5.setId(105); btn5.setText("main thread's message to other thread"); btn5.setOnClickListener(this); layout.addView(btn5, param); btn6 = new Button(this); btn6.setId(106); btn6.setText("exit"); btn6.setOnClickListener(this); layout.addView(btn6, 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); //主线程要发送消息给other thread， 这里创建那个other thread receiveMessageThread = new ReceiveMessageThread(); receiveMessageThread.start(); } //implement the OnClickListener interface @Override public void onClick(View v) { switch(v.getId()){ case 101: //主线程发送消息给自己 Looper looper; looper = Looper.myLooper(); //get the Main looper related with the main thread //如果不给任何参数的话会用当前线程对应的Looper(这里就是Main Looper)为Handler里面的成员mLooper赋值 mHandler = new EventHandler(looper); //mHandler = new EventHandler(); // 清除整个MessageQueue里的消息 mHandler.removeMessages(0); String obj = "This main thread's message and received by itself!"; //得到Message对象 Message m = mHandler.obtainMessage(1, 1, 1, obj); // 将Message对象送入到main thread的MessageQueue里面 mHandler.sendMessage(m); break; case 102: //other线程发送消息给主线程 postRunnable = false; noLooerThread = new NoLooperThread(); noLooerThread.start(); break; case 103: //other thread获取它自己发送的消息 tv.setText("please look at the error level log for other thread received message"); ownLooperThread = new OwnLooperThread(); ownLooperThread.start(); break; case 104: //other thread通过Post Runnable方式发送消息给主线程 postRunnable = true; noLooerThread = new NoLooperThread(); noLooerThread.start(); break; case 105: //主线程发送消息给other thread if(null!=mOtherThreadHandler){ tv.setText("please look at the error level log for other thread received message from main thread"); String msgObj = "message from mainThread"; Message mainThreadMsg = mOtherThreadHandler.obtainMessage(1, 1, 1, msgObj); mOtherThreadHandler.sendMessage(mainThreadMsg); } break; case 106: finish(); break; } } class EventHandler extends Handler { public EventHandler(Looper looper) { super(looper); } public EventHandler() { super(); } public void handleMessage(Message msg) { //可以根据msg.what执行不同的处理，这里没有这么做 switch(msg.what){ case 1: tv.setText((String)msg.obj); break; case 2: tv.setText((String)msg.obj); noLooerThread.stop(); break; case 3: //不能在非主线程的线程里面更新UI，所以这里通过Log打印收到的消息 Log.e(sTag, (String)msg.obj); ownLooperThread.stop(); break; default: //不能在非主线程的线程里面更新UI，所以这里通过Log打印收到的消息 Log.e(sTag, (String)msg.obj); break; } } } //NoLooperThread class NoLooperThread extends Thread{ private EventHandler mNoLooperThreadHandler; public void run() { Looper myLooper, mainLooper; myLooper = Looper.myLooper(); mainLooper = Looper.getMainLooper(); //这是一个static函数 String obj; if(myLooper == null){ mNoLooperThreadHandler = new EventHandler(mainLooper); obj = "NoLooperThread has no looper and handleMessage function executed in main thread!"; } else { mNoLooperThreadHandler = new EventHandler(myLooper); obj = "This is from NoLooperThread self and handleMessage function executed in NoLooperThread!"; } mNoLooperThreadHandler.removeMessages(0); if(false == postRunnable){ //send message to main thread Message m = mNoLooperThreadHandler.obtainMessage(2, 1, 1, obj); mNoLooperThreadHandler.sendMessage(m); Log.e(sTag, "NoLooperThread id:" + this.getId()); }else{ //下面new出来的实现了Runnable接口的对象中run函数是在Main Thread中执行，不是在NoLooperThread中执行 //注意Runnable是一个接口，它里面的run函数被执行时不会再新建一个线程 //您可以在run上加断点然后在eclipse调试中看它在哪个线程中执行 mNoLooperThreadHandler.post(new Runnable(){ @Override public void run() { tv.setText("update UI through handler post runnalbe mechanism!"); noLooerThread.stop(); } }); } } } //OwnLooperThread has his own message queue by execute Looper.prepare(); class OwnLooperThread extends Thread{ private EventHandler mOwnLooperThreadHandler; public void run() { Looper.prepare(); Looper myLooper, mainLooper; myLooper = Looper.myLooper(); mainLooper = Looper.getMainLooper(); //这是一个static函数 String obj; if(myLooper == null){ mOwnLooperThreadHandler = new EventHandler(mainLooper); obj = "OwnLooperThread has no looper and handleMessage function executed in main thread!"; } else { mOwnLooperThreadHandler = new EventHandler(myLooper); obj = "This is from OwnLooperThread self and handleMessage function executed in NoLooperThread!"; } mOwnLooperThreadHandler.removeMessages(0); //给自己发送消息 Message m = mOwnLooperThreadHandler.obtainMessage(3, 1, 1, obj); mOwnLooperThreadHandler.sendMessage(m); Looper.loop(); } } //ReceiveMessageThread has his own message queue by execute Looper.prepare(); class ReceiveMessageThread extends Thread{ public void run() { Looper.prepare(); mOtherThreadHandler = new Handler(){ public void handleMessage(Message msg) { Log.e(sTag, (String)msg.obj); } }; Looper.loop(); } } } 说明（代码详细解释请见后文）： 使用Looper.myLooper静态方法可以取得当前线程的Looper对象。 使用mHandler = new EevntHandler(Looper.myLooper()); 可建立用来处理当前线程的Handler对象；其中，EevntHandler是Handler的子类。 使用mHandler = new EevntHandler(Looper.getMainLooper()); 可建立用来处理main线程的Handler对象；其中，EevntHandler是Handler的子类。 1.5.1.主线程给自己发送消息示例 主线程发送消息： 在onClick的case 101中创建一个继承自Handler的EventHandler对象，然后获取一个消息，然后通过EventHandler对象调用 sendMessage把消息发送到主线程的MessageQueue中。主线程由系统创建，系统会给它建立一个Looper对象和 MessageQueue，所以可以接收消息。这里只要根据主线程的Looper对象初始化EventHandler对象，就可以通过 EventHandler对象发送消息到主线程的消息队列中。 主线程处理消息： 这里是通过EventHandler的handleMessage函数处理的，其中收到的Message对象中what值为一的消息就是发送给它的，然后把消息里面附带的字符串在TextView上显示出来。 1.5.2.其他线程给主线程发送消息示例 其他线程发送消息（这里是说不使用Runnable作为callback的消息）： 首先 postRunnable设为false，表示不通过Runnable方式进行消息相关的操作。然后启动线程noLooerThread，然后以主线程的 Looper对象为参数建立EventHandler的对象mNoLooperThreadHandler，然后获取一个Message并把一个字符串赋 值给它的一个成员obj，然后通过mNoLooperThreadHandler把消息发送到主线程的MessageQueue中。 主线程处理消息： 这里是通过EventHandler的handleMessage函数处理的，其中收到的Message对象中what值为二的消息就是上面发送给它的，然后把消息里面附带的字符串在TextView上显示出来。 1.5.3.其他线程给自己发送消息示例 其他线程发送消息： 其他非主线程建立后没有自己的Looper对象，所以也没有MessageQueue，需要给非主线程发送消息时需要建立 MessageQueue以便接收消息。下面说明如何给自己建立MessageQueue和Looper对象。从OwnLooperThread的run 函数中可以看见有一个 Looper.prepare()调用，这个就是用来建立非主线程的MessageQueue和Looper对象的。 所以这里的发送消息过程是建立线程mOwnLooperThread，然后线程建立自己的Looper和MessageQueue对象，然后根据 上面建立的Looper对象建立对应的EventHandler对象mOwnLooperThreadHandler，然后由 mOwnLooperThreadHandler建立消息并且发送到自己的MessageQueue里面。 其他线程处理接收的消息： 线程要接收消息需要在run函数中调用Looper.loop()，然后loop函数会从MessageQueue中取出消息交给对应的 Handler对象 mOwnLooperThreadHandler处理，在mOwnLooperThreadHandler的handleMessage函数中会把 Message对象中what值为三的消息（上面发送的消息）在Log中打印出来，可以通过Logcat工具查看log。 1.5.4.其他线程以Runnable为消息参数给主线程发送消息示例 其他线程发送消息（这里是说使用Runnable作为callback的消息）： 首先 postRunnable设为true，表示通过Runnable方式进行消息相关的操作。然后启动线程noLooerThread，然后以主线程的 Looper对象为参数建立EventHandler的对象mNoLooperThreadHandler，然后获取一个Message并把一个字符串赋 值给它的一个成员obj，然后通过mNoLooperThreadHandler把消息发送到主线程的MessageQueue中。 主线程处理消息： 主线程收到上面发送的Message后直接运行上面Runnable对象中的run函数进行相应的操作。run函数通过Log打印一个字符串，可以通过Logcat工具查看log。 1.5.5.主线程给其他线程发送消息示例 主线程发送消息： 这里首先要求线程receiveMessageThread运行（在onCreate函数中完成），并且准备好自己的Looper和 MessageQueue（这个通过ReceiveMessageThread中的run函数中的Looper.prepare()调用完成），然后根据 建立的Looper对象初始化Handler对象mOtherThreadHandler。然后在onClick的case 105中由mOtherThreadHandler建立一个消息（消息中有一个字符串对象）并且发送到线程receiveMessageThread中的 MessageQueue中。 其他线程处理接收的消息： 线程要接收消息需要在run函数中调用Looper.loop()，然后loop函数会从MessageQueue中取出消息交给对应的 Handler对象mOtherThreadHandler处理，在mOtherThreadHandler的handleMessage函数中会把 Message对象中的字符串对象在Log中打印出来，可以通过Logcat工具查看log。 
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posted on 2012-04-23 18:23
Bluesea 阅读(1528)
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