1.活用Android線程間通信的Message機制 1.1.Message 代碼在frameworks\base\core\java\android\Os\Message.java中。 Message.obtain函數：有多個obtain函數，主要功能一樣，只是參數不一樣。作用是從Message Pool中取出一個Message，如果Message Pool中已經沒有Message可取則新建一個Message返回，同時用對應的參數給得到的Message對象賦值。 Message Pool：大小為10個；通過Message.mPool->（Message并且Message.next）-> （Message并且Message.next）-> （Message并且Message.next）...構造一個Message Pool。Message Pool的第一個元素直接new出來，然后把Message.mPool（static類的static變量）指向它。其他的元素都是使用完的 Message通過Message的recycle函數清理后放到Message Pool（通過Message Pool最后一個Message的next指向需要回收的Message的方式實現）。下圖為Message Pool的結構： 
1.2.MessageQueue MessageQueue里面有一個收到的Message的對列： MessageQueue.mMessages(static變量)->( Message并且Message.next)-> ( Message并且Message.next)->...，下圖為接收消息的消息隊列： 
上層代碼通過Handler的sendMessage等函數放入一個message到MessageQueue里面時最終會調用 MessageQueue的 enqueueMessage函數。enqueueMessage根據上面的接收的Message的隊列的構造把接收到的Message放入隊列中。 MessageQueue的removeMessages函數根據上面的接收的Message的隊列的構造把接收到的Message從隊列中刪除，并且調用對應Message對象的recycle函數把不用的Message放入Message Pool中。 1.3.Looper Looper對象的創建是通過prepare函數，而且每一個Looper對象會和一個線程關聯 Java代碼
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對象創建時會創建一個MessageQueue，主線程默認會創建一個Looper從而有MessageQueue，其他線程默認是 沒有 MessageQueue的不能接收Message，如果需要接收Message則需要通過prepare函數創建一個MessageQueue。具體操 作請見示例代碼。 Java代碼
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函數只給主線程調用（系統處理，程序員不用處理），它會調用prepare建立Looper對象和MessageQueue。 Java代碼
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函數從MessageQueue中從前往后取出Message，然后通過Handler的dispatchMessage函數進行消息的 處理（可見消息的處理是Handler負責的），消息處理完了以后通過Message對象的recycle函數放到Message Pool中，以便下次使用，通過Pool的處理提供了一定的內存管理從而加速消息對象的獲取。至于需要定時處理的消息如何做到定時處理，請見 MessageQueue的next函數，它在取Message來進行處理時通過判斷MessageQueue里面的Message是否符合時間要求來決 定是否需要把Message取出來做處理，通過這種方式做到消息的定時處理。 Java代碼
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代碼
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); } 獲取消息：直接通過Message的obtain方法獲取一個Message對象。 Java代碼
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); } 發送消息：通過MessageQueue的enqueueMessage把Message對象放到MessageQueue的接收消息隊列中 Java代碼
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 }
線程如何處理MessageQueue中接收的消息：在Looper的loop函數中循環取出MessageQueue的接收消息隊列中的消息， 然后調用 Hander的dispatchMessage函數對消息進行處理，至于如何處理（相應消息）則由用戶指定（三個方法，優先級從高到低：Message里 面的Callback，一個實現了Runnable接口的對象，其中run函數做處理工作；Handler里面的mCallback指向的一個實現了 Callback接口的對象，里面的handleMessage進行處理；處理消息Handler對象對應的類繼承并實現了其中 handleMessage函數，通過這個實現的handleMessage函數處理消息）。 Java代碼
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說明：Runnable只是一個接口，實現了這個接口的類對應的對象也只是個普通的對象，并不是一個Java中的Thread。Thread類經常使用Runnable，很多人有誤解，所以這里澄清一下。 從上可知以下關系圖： 
其中清理Message是Looper里面的loop函數指把處理過的Message放到Message的Pool里面去，如果里面已經超過最大值10個，則丟棄這個Message對象。 調用Handler是指Looper里面的loop函數從MessageQueue的接收消息隊列里面取出消息，然后根據消息指向的Handler對象調用其對應的處理方法。 1.5.代碼示例 下面我們會以android實例來展示對應的功能，程序界面于下： 
程序代碼如下，后面部分有代碼說明： Java代碼
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 //主線程要發送消息給other thread， 這里創建那個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 //主線程發送消息給自己
89 Looper looper;
90 looper = Looper.myLooper(); //get the Main looper related with the main thread
91 //如果不給任何參數的話會用當前線程對應的Looper(這里就是Main Looper)為Handler里面的成員mLooper賦值
92 mHandler = new EventHandler(looper);
93 //mHandler = new EventHandler();
94 // 清除整個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對象
98 Message m = mHandler.obtainMessage(1, 1, 1, obj);
99 // 將Message對象送入到main thread的MessageQueue里面
100 mHandler.sendMessage(m);
101 break;
102 case 102:
103 //other線程發送消息給主線程
104 postRunnable = false;
105 noLooerThread = new NoLooperThread();
106 noLooerThread.start();
107 break;
108 case 103:
109 //other thread獲取它自己發送的消息
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通過Post Runnable方式發送消息給主線程
116 postRunnable = true;
117 noLooerThread = new NoLooperThread();
118 noLooerThread.start();
119 break;
120 case 105:
121 //主線程發送消息給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 //可以根據msg.what執行不同的處理，這里沒有這么做
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 //不能在非主線程的線程里面更新UI，所以這里通過Log打印收到的消息
154 Log.e(sTag, (String)msg.obj);
155 ownLooperThread.stop();
156 break;
157 default:
158 //不能在非主線程的線程里面更新UI，所以這里通過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(); //這是一個static函數
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出來的實現了Runnable接口的對象中run函數是在Main Thread中執行，不是在NoLooperThread中執行
188 //注意Runnable是一個接口，它里面的run函數被執行時不會再新建一個線程
189 //您可以在run上加斷點然后在eclipse調試中看它在哪個線程中執行
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(); //這是一個static函數
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 //給自己發送消息
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); //主線程要發送消息給other thread， 這里創建那個other thread receiveMessageThread = new ReceiveMessageThread(); receiveMessageThread.start(); } //implement the OnClickListener interface @Override public void onClick(View v) { switch(v.getId()){ case 101: //主線程發送消息給自己 Looper looper; looper = Looper.myLooper(); //get the Main looper related with the main thread //如果不給任何參數的話會用當前線程對應的Looper(這里就是Main Looper)為Handler里面的成員mLooper賦值 mHandler = new EventHandler(looper); //mHandler = new EventHandler(); // 清除整個MessageQueue里的消息 mHandler.removeMessages(0); String obj = "This main thread's message and received by itself!"; //得到Message對象 Message m = mHandler.obtainMessage(1, 1, 1, obj); // 將Message對象送入到main thread的MessageQueue里面 mHandler.sendMessage(m); break; case 102: //other線程發送消息給主線程 postRunnable = false; noLooerThread = new NoLooperThread(); noLooerThread.start(); break; case 103: //other thread獲取它自己發送的消息 tv.setText("please look at the error level log for other thread received message"); ownLooperThread = new OwnLooperThread(); ownLooperThread.start(); break; case 104: //other thread通過Post Runnable方式發送消息給主線程 postRunnable = true; noLooerThread = new NoLooperThread(); noLooerThread.start(); break; case 105: //主線程發送消息給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) { //可以根據msg.what執行不同的處理，這里沒有這么做 switch(msg.what){ case 1: tv.setText((String)msg.obj); break; case 2: tv.setText((String)msg.obj); noLooerThread.stop(); break; case 3: //不能在非主線程的線程里面更新UI，所以這里通過Log打印收到的消息 Log.e(sTag, (String)msg.obj); ownLooperThread.stop(); break; default: //不能在非主線程的線程里面更新UI，所以這里通過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(); //這是一個static函數 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出來的實現了Runnable接口的對象中run函數是在Main Thread中執行，不是在NoLooperThread中執行 //注意Runnable是一個接口，它里面的run函數被執行時不會再新建一個線程 //您可以在run上加斷點然后在eclipse調試中看它在哪個線程中執行 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(); //這是一個static函數 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); //給自己發送消息 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(); } } } 說明（代碼詳細解釋請見后文）： 使用Looper.myLooper靜態方法可以取得當前線程的Looper對象。 使用mHandler = new EevntHandler(Looper.myLooper()); 可建立用來處理當前線程的Handler對象；其中，EevntHandler是Handler的子類。 使用mHandler = new EevntHandler(Looper.getMainLooper()); 可建立用來處理main線程的Handler對象；其中，EevntHandler是Handler的子類。 1.5.1.主線程給自己發送消息示例 主線程發送消息： 在onClick的case 101中創建一個繼承自Handler的EventHandler對象，然后獲取一個消息，然后通過EventHandler對象調用 sendMessage把消息發送到主線程的MessageQueue中。主線程由系統創建，系統會給它建立一個Looper對象和 MessageQueue，所以可以接收消息。這里只要根據主線程的Looper對象初始化EventHandler對象，就可以通過 EventHandler對象發送消息到主線程的消息隊列中。 主線程處理消息： 這里是通過EventHandler的handleMessage函數處理的，其中收到的Message對象中what值為一的消息就是發送給它的，然后把消息里面附帶的字符串在TextView上顯示出來。 1.5.2.其他線程給主線程發送消息示例 其他線程發送消息（這里是說不使用Runnable作為callback的消息）： 首先 postRunnable設為false，表示不通過Runnable方式進行消息相關的操作。然后啟動線程noLooerThread，然后以主線程的 Looper對象為參數建立EventHandler的對象mNoLooperThreadHandler，然后獲取一個Message并把一個字符串賦 值給它的一個成員obj，然后通過mNoLooperThreadHandler把消息發送到主線程的MessageQueue中。 主線程處理消息： 這里是通過EventHandler的handleMessage函數處理的，其中收到的Message對象中what值為二的消息就是上面發送給它的，然后把消息里面附帶的字符串在TextView上顯示出來。 1.5.3.其他線程給自己發送消息示例 其他線程發送消息： 其他非主線程建立后沒有自己的Looper對象，所以也沒有MessageQueue，需要給非主線程發送消息時需要建立 MessageQueue以便接收消息。下面說明如何給自己建立MessageQueue和Looper對象。從OwnLooperThread的run 函數中可以看見有一個 Looper.prepare()調用，這個就是用來建立非主線程的MessageQueue和Looper對象的。 所以這里的發送消息過程是建立線程mOwnLooperThread，然后線程建立自己的Looper和MessageQueue對象，然后根據 上面建立的Looper對象建立對應的EventHandler對象mOwnLooperThreadHandler，然后由 mOwnLooperThreadHandler建立消息并且發送到自己的MessageQueue里面。 其他線程處理接收的消息： 線程要接收消息需要在run函數中調用Looper.loop()，然后loop函數會從MessageQueue中取出消息交給對應的 Handler對象 mOwnLooperThreadHandler處理，在mOwnLooperThreadHandler的handleMessage函數中會把 Message對象中what值為三的消息（上面發送的消息）在Log中打印出來，可以通過Logcat工具查看log。 1.5.4.其他線程以Runnable為消息參數給主線程發送消息示例 其他線程發送消息（這里是說使用Runnable作為callback的消息）： 首先 postRunnable設為true，表示通過Runnable方式進行消息相關的操作。然后啟動線程noLooerThread，然后以主線程的 Looper對象為參數建立EventHandler的對象mNoLooperThreadHandler，然后獲取一個Message并把一個字符串賦 值給它的一個成員obj，然后通過mNoLooperThreadHandler把消息發送到主線程的MessageQueue中。 主線程處理消息： 主線程收到上面發送的Message后直接運行上面Runnable對象中的run函數進行相應的操作。run函數通過Log打印一個字符串，可以通過Logcat工具查看log。 1.5.5.主線程給其他線程發送消息示例 主線程發送消息： 這里首先要求線程receiveMessageThread運行（在onCreate函數中完成），并且準備好自己的Looper和 MessageQueue（這個通過ReceiveMessageThread中的run函數中的Looper.prepare()調用完成），然后根據 建立的Looper對象初始化Handler對象mOtherThreadHandler。然后在onClick的case 105中由mOtherThreadHandler建立一個消息（消息中有一個字符串對象）并且發送到線程receiveMessageThread中的 MessageQueue中。 其他線程處理接收的消息： 線程要接收消息需要在run函數中調用Looper.loop()，然后loop函數會從MessageQueue中取出消息交給對應的 Handler對象mOtherThreadHandler處理，在mOtherThreadHandler的handleMessage函數中會把 Message對象中的字符串對象在Log中打印出來，可以通過Logcat工具查看log。 
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posted on 2012-04-23 18:23
Bluesea 閱讀(1553)
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