第81章、Handle-Message-Looper消息機制之二（從零開始學Android）

本章著重通過一個網絡通信應用再次了解一下Handle、Message、Looper實際用法。

 

一、設計界面

1、布局文件

打開res/layout/activity_main.xml文件。
輸入以下代碼：

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1. <?xml version="1.0" encoding="utf-8"?>  
2. <LinearLayout   
3.     xmlns:android="http://schemas.android.com/apk/res/android"  
4.     android:layout_width="match_parent"  
5.     android:layout_height="match_parent"  
6.     android:orientation="vertical" >  
7.   
8.     <TextView  
9.         android:id="@+id/tvmsg"  
10.         android:layout_width="wrap_content"  
11.         android:layout_height="wrap_content"  
12.         android:text="" />  
13.   
14. </LinearLayout>  

 

二、程序文件

打開“src/com.genwoxue.hml/MainActivity.java”文件。
然後輸入以下代碼：

[java] view plain copy  

1. package com.genwoxue.hml;  
2.   
3. import java.io.ByteArrayOutputStream;  
4. import java.io.InputStream;  
5.   
6. import org.apache.http.HttpEntity;  
7. import org.apache.http.HttpResponse;  
8. import org.apache.http.client.HttpClient;  
9. import org.apache.http.client.methods.HttpGet;  
10. import org.apache.http.impl.client.DefaultHttpClient;  
11. import android.app.Activity;    
12. import android.app.ProgressDialog;  
13. import android.content.DialogInterface;  
14. import android.os.Bundle;    
15. import android.os.Handler;    
16. import android.os.Looper;    
17. import android.os.Message;    
18. import android.util.Log;    
19. import android.widget.TextView;    
20.   
21. public class MainActivity extends Activity{    
22.             
23.         private String TAG = "HandlerTest";    
24.         private ReceiveMessageThread receiveMessageThread =null;    
25.         private EventHandler mHandler = null;     
26.         private TextView tv = null;   
27.         ProgressDialog pdialog;      
28.           
29.         @Override    
30.         public void onCreate(Bundle savedInstanceState) {    
31.               
32.             super.onCreate(savedInstanceState);    
33.             setContentView(R.layout.activity_main);    
34.             tv = (TextView)super.findViewById(R.id.tvmsg);    
35.               
36.             //創建對話框  
37.             pdialog = new ProgressDialog(this);  
38.             //設置對話框取消按鈕  
39.             pdialog.setButton("cancel", new DialogInterface.OnClickListener() {   
40.                 public void onClick(DialogInterface dialog, int i) {      
41.                     dialog.cancel();          
42.                 }            
43.             });            
44.               
45.             //對話對話框取消事件  
46.             pdialog.setOnCancelListener(new DialogInterface.OnCancelListener() {       
47.                 public void onCancel(DialogInterface dialog) {             
48.                     finish();             
49.                 }            
50.             });            
51.           
52.             //初始化對話框  
53.             pdialog.setCancelable(true);     
54.             pdialog.setMax(100);           
55.             pdialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);       
56.             pdialog.show();         
57.   
58.             tv.setText("正在下載中……");   
59.               
60.             //啟動線程  
61.             receiveMessageThread = new ReceiveMessageThread();      
62.             receiveMessageThread.start();       
63.               
64.         }    
65.           
66.           
67.         //消息處理    
68.         class EventHandler extends Handler{    
69.             public EventHandler(Looper looper){    
70.                 super(looper);    
71.             }    
72.                 
73.             public EventHandler(){    
74.                 super();    
75.             }    
76.             @Override    
77.             public void handleMessage(Message msg) {    
78.                 super.handleMessage(msg);    
79.                 switch(msg.what){    
80.                 case 1:     //消息為1傳遞進度  
81.                     int pos=Integer.valueOf((String)msg.obj);  
82.                     tv.setText((String)msg.obj);   
83.                     pdialog.setProgress(pos);   
84.                     break;    
85.                 case 2:    //消息為2，顯示結果  
86.                     tv.setText((String)msg.obj);   
87.                     pdialog.dismiss();  
88.                     break;    
89.                 default:    
90.                     Log.e(TAG,(String)msg.obj);    
91.                     break;    
92.                 }    
93.             }    
94.         }    
95.            
96.         //創建子線程，下載網頁文件  
97.         class ReceiveMessageThread extends Thread {    
98.                 
99.             @Override    
100.             public void run(){    
101.                 Looper.prepare();    
102.                   System.out.println("thread is start!");  
103.                       
104.                     String result = null;  
105.                     try{                 
106.                         HttpClient client = new DefaultHttpClient();         
107.                         HttpGet get = new HttpGet("http://www.genwoxue.com");        
108.                         HttpResponse response = client.execute(get);          
109.                         HttpEntity entity = response.getEntity();              
110.                         long length = entity.getContentLength();                
111.                         InputStream is = entity.getContent();                  
112.                         System.out.print(length);  
113.                         if(is != null) {                       
114.                             ByteArrayOutputStream baos = new ByteArrayOutputStream();            
115.                             byte[] buf = new byte[128];                    
116.                             int ch = -1;                     
117.                             int count = 0;            
118.                             int percent=0;  
119.                             while((ch = is.read(buf)) != -1) {          
120.                                 baos.write(buf, 0, ch);     
121.                                   
122.                                 count += ch;                          
123.                                 if(length > 0) {          
124.                                       
125.                                     percent=(int) ((count / (float) length) * 100);  
126.                                       
127.                                     Looper looper = Looper.getMainLooper();      
128.                                     mHandler = new EventHandler(looper);    
129.                                     mHandler.removeMessages(1);  
130.                                     Message msg =new Message();  
131.                                     if(percent<100){  
132.                                         msg.what=1;  
133.                                         msg.obj= String.valueOf(percent);    
134.                                     }  
135.                                     else{  
136.                                         result = new String(baos.toByteArray());  
137.                                         msg.what=2;  
138.                                         msg.obj= String.valueOf(result);  
139.                                     }  
140.                                           
141.                                      // 將Message對象送入到main thread的MessageQueue裡面     
142.                                      MainActivity.this.mHandler.sendMessage(msg);  
143.                                           
144.                                     }                           
145.                                     Thread.sleep(50);    // 讓線程休眠50ms                  
146.                                 }            
147.                                         
148.                         }                
149.                     } catch(Exception e) {           
150.                         e.printStackTrace();          
151.                     }               
152.                       
153.                  Looper.loop();    
154.             }    
155.         }    
156.             
157. }    

 

三、配置文件

打開“AndroidManifest.xml”文件。

然後輸入以下代碼：

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1. <?xml version="1.0" encoding="utf-8"?>  
2. <manifest xmlns:android="http://schemas.android.com/apk/res/android"  
3.     package="com.genwoxue.hml"  
4.     android:versionCode="1"  
5.     android:versionName="1.0" >  
6.   
7.     <uses-sdk  
8.         android:minSdkVersion="10"  
9.         android:targetSdkVersion="15" />  
10.       
11.     <uses-permission android:name="android.permission.INTERNET"/>  
12.   
13.     <application  
14.         android:allowBackup="true"  
15.         android:icon="@drawable/ic_launcher"  
16.         android:label="@string/app_name"  
17.         android:theme="@style/AppTheme" >  
18.         <activity  
19.             android:name="com.genwoxue.hml.MainActivity"  
20.             android:label="@string/app_name" >  
21.             <intent-filter>  
22.                 <action android:name="android.intent.action.MAIN" />  
23.                 <category android:name="android.intent.category.LAUNCHER" />  
24.             </intent-filter>  
25.         </activity>  
26.     </application>  
27.   
28. </manifest>  

 

注意：由於要訪問互聯網，需要在AndroidManifest.xml文件中添加權限：

<uses-permission android:name="android.permission.INTERNET"/>

四、運行結果