第81章、Handle-Message-Looper消息机制之二（从零开始学Android）

　　本章着重通过一个网络通信应用再次了解一下Handle、Message、Looper实际用法。

 

一、设计界面

　　1、布局文件

　　打开res/layout/activity_main.xml文件。
　　输入以下代码：

<?xml version="1.0" encoding="utf-8"?><LinearLayout     xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:orientation="vertical" >    <TextView        android:id="@+id/tvmsg"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="" /></LinearLayout>

二、程序文件

　　打开“src/com.genwoxue.hml/MainActivity.java”文件。
　　然后输入以下代码：

package com.genwoxue.hml;import java.io.ByteArrayOutputStream;import java.io.InputStream;import org.apache.http.HttpEntity;import org.apache.http.HttpResponse;import org.apache.http.client.HttpClient;import org.apache.http.client.methods.HttpGet;import org.apache.http.impl.client.DefaultHttpClient;import android.app.Activity;  import android.app.ProgressDialog;import android.content.DialogInterface;import android.os.Bundle;  import android.os.Handler;  import android.os.Looper;  import android.os.Message;  import android.util.Log;  import android.widget.TextView;  public class MainActivity extends Activity{            private String TAG = "HandlerTest";      private ReceiveMessageThread receiveMessageThread =null;      private EventHandler mHandler = null;       private TextView tv = null;     ProgressDialog pdialog;            @Override      public void onCreate(Bundle savedInstanceState) {              super.onCreate(savedInstanceState);          setContentView(R.layout.activity_main);          tv = (TextView)super.findViewById(R.id.tvmsg);                  //创建对话框        pdialog = new ProgressDialog(this);        //设置对话框取消按钮        pdialog.setButton("cancel", new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int i) {    dialog.cancel();        }          });                  //对话对话框取消事件        pdialog.setOnCancelListener(new DialogInterface.OnCancelListener() {     public void onCancel(DialogInterface dialog) {           finish();           }                  });                      //初始化对话框pdialog.setCancelable(true);   pdialog.setMax(100);         pdialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);     pdialog.show();       tv.setText("正在下载中……"); //启动线程receiveMessageThread = new ReceiveMessageThread();    receiveMessageThread.start();         }              //消息处理      class EventHandler extends Handler{          public EventHandler(Looper looper){              super(looper);          }                    public EventHandler(){              super();          }          @Override          public void handleMessage(Message msg) {              super.handleMessage(msg);              switch(msg.what){              case 1:  //消息为1传递进度                int pos=Integer.valueOf((String)msg.obj);                tv.setText((String)msg.obj);                 pdialog.setProgress(pos);                 break;              case 2:    //消息为2，显示结果                tv.setText((String)msg.obj);                 pdialog.dismiss();                break;           default:                  Log.e(TAG,(String)msg.obj);                  break;              }          }      }           //创建子线程，下载网页文件    class ReceiveMessageThread extends Thread {                    @Override          public void run(){              Looper.prepare();            System.out.println("thread is start!");                    String result = null;try{               HttpClient client = new DefaultHttpClient();       HttpGet get = new HttpGet("http://www.genwoxue.com");      HttpResponse response = client.execute(get);        HttpEntity entity = response.getEntity();            long length = entity.getContentLength();              InputStream is = entity.getContent();                System.out.print(length);if(is != null) {                     ByteArrayOutputStream baos = new ByteArrayOutputStream();          byte[] buf = new byte[128];                  int ch = -1;                   int count = 0;          int percent=0;while((ch = is.read(buf)) != -1) {        baos.write(buf, 0, ch);   count += ch;                        if(length > 0) {        percent=(int) ((count / (float) length) * 100);Looper looper = Looper.getMainLooper();                mHandler = new EventHandler(looper);              mHandler.removeMessages(1);            Message msg =new Message();            if(percent<100){            msg.what=1;            msg.obj= String.valueOf(percent);              }            else{            result = new String(baos.toByteArray());            msg.what=2;            msg.obj= String.valueOf(result);            }                     // 将Message对象送入到main thread的MessageQueue里面    MainActivity.this.mHandler.sendMessage(msg);            }                         Thread.sleep(50);    // 让线程休眠50ms                }                    }              } catch(Exception e) {         e.printStackTrace();        }                                      Looper.loop();          }      }        }  

三、配置文件

　　打开“AndroidManifest.xml”文件。

　　然后输入以下代码：

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="com.genwoxue.hml"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk        android:minSdkVersion="10"        android:targetSdkVersion="15" />        <uses-permission android:name="android.permission.INTERNET"/>    <application        android:allowBackup="true"        android:icon="@drawable/ic_launcher"        android:label="@string/app_name"        android:theme="@style/AppTheme" >        <activity            android:name="com.genwoxue.hml.MainActivity"            android:label="@string/app_name" >            <intent-filter>                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application></manifest>

注意：由于要访问互联网，需要在AndroidManifest.xml文件中添加权限：

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

四、运行结果