android中Message机制的灵活应用
16lz
2021-12-04
android中Message机制的灵活应用
关键字: 消息机制 handler looper 线程间通信 message messagequeue
引用
来自easyandroid论坛，原文：http://www.easyandroid.com/bbs/viewthread.php?tid=33
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
1. public static final void prepareMainLooper() {
2. prepare();
3. setMainLooper(myLooper());
4. if (Process.supportsProcesses()) {
5. myLooper().mQueue.mQuitAllowed = false;
6. }
7. }
public static final void prepareMainLooper() {
prepare();
setMainLooper(myLooper());
if (Process.supportsProcesses()) {
myLooper().mQueue.mQuitAllowed = false;
}
}
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. }
public static final void loop() {
Looper me = myLooper();
MessageQueue queue = me.mQueue;
while (true) {
Message msg = queue.next(); // might block
//if (!me.mRun) {
// break;
//}
if (msg != null) {
if (msg.target == null) {
// No target is a magic identifier for the quit message
return;
}
if (me.mLogging!= null)
me.mLogging.println(">>>>> Dispatching to " + msg.target + " "+ msg.callback + ": " + msg.what);
msg.target.dispatchMessage(msg);
if (me.mLogging!= null)
me.mLogging.println("<<<<< Finished to" + msg.target + " "+ msg.callback);
msg.recycle();
}
}
}
1.4.Handler
Handler的构造函数表示Handler会有成员变量指向Looper和MessageQueue，后面我们会看到没什么需要这些引用；至于callback是实现了Callback接口的对象，后面会看到这个对象的作用。
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
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. }
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;
}
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。
关键字: 消息机制 handler looper 线程间通信 message messagequeue
引用
来自easyandroid论坛，原文：http://www.easyandroid.com/bbs/viewthread.php?tid=33
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
1. public static final void prepareMainLooper() {
2. prepare();
3. setMainLooper(myLooper());
4. if (Process.supportsProcesses()) {
5. myLooper().mQueue.mQuitAllowed = false;
6. }
7. }
public static final void prepareMainLooper() {
prepare();
setMainLooper(myLooper());
if (Process.supportsProcesses()) {
myLooper().mQueue.mQuitAllowed = false;
}
}
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. }
public static final void loop() {
Looper me = myLooper();
MessageQueue queue = me.mQueue;
while (true) {
Message msg = queue.next(); // might block
//if (!me.mRun) {
// break;
//}
if (msg != null) {
if (msg.target == null) {
// No target is a magic identifier for the quit message
return;
}
if (me.mLogging!= null)
me.mLogging.println(">>>>> Dispatching to " + msg.target + " "+ msg.callback + ": " + msg.what);
msg.target.dispatchMessage(msg);
if (me.mLogging!= null)
me.mLogging.println("<<<<< Finished to" + msg.target + " "+ msg.callback);
msg.recycle();
}
}
}
1.4.Handler
Handler的构造函数表示Handler会有成员变量指向Looper和MessageQueue，后面我们会看到没什么需要这些引用；至于callback是实现了Callback接口的对象，后面会看到这个对象的作用。
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
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. }
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;
}
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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