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：

<?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