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

转自：http://blog.csdn.net/jianghuiquan/article/details/8641072

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：

[html] view
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<?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：

[java] view
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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：

[html] view
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<?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