Android多任务多线程下载

打算实现一个下载功能，当然理想的功能要支持多任务下载、多线程下载、断点续传的功能，我想一步一步来，首先困难摆在了多任务这里。

开始的思路是在一个Service中启动下载的流操作，然后通过Service中声明一个Activity中的Handler更新UI(比如进度条。。。)

可是我发现在Service中声明一个Activity中的Handler是做不到的（可能只是我做不到吧，无法申请内存）

于是，我决定在Activity中直接启动线程，让其运行，调用自身的Handler来更新UI，没想到在这个下载Activity onPause()的时候，线程还是活的，也就是说可以继续下载，下例是我做的一个两个任务同时下载的小例子，后面会把理想中的功能都陆续添加上的。

main.xml配置：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"> 
    <ProgressBar 
        android:id="@+id/progressBar1" 
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        style="?android:attr/progressBarStyleHorizontal"></ProgressBar> 
    <TextView 
        android:id="@+id/textView1" 
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        /> 
    <ProgressBar 
        android:id="@+id/progressBar2"
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        style="?android:attr/progressBarStyleHorizontal"></ProgressBar> 
    <TextView 
        android:id="@+id/textView2" 
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        /> 
</LinearLayout>

AndroidManifest.xml配置：

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="sms.down" 
    android:versionCode="1" 
    android:versionName="1.0"> 
    <uses-sdk android:minSdkVersion="9" /> 
  
    <application android:icon="@drawable/icon" android:label="@string/app_name"> 
        <activity android:name=".MulThreadDownload" 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> 
  
    <!-- 访问 internet 权限 -->
    <uses-permission android:name="android.permission.INTERNET" /> 
    <uses-permission android:name="android.permission.CALL_PHONE" /> 
    <uses-permission android:name="android.permission.SEND_SMS" /> 
    <uses-permission android:name="android.permission.READ_CONTACTS" /> 
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> 
    <uses-permission android:name="android.permission.READ_PHONE_STATE" /> 
</manifest>

Activity程序：

package sms.down; 
  
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream; 
import java.net.HttpURLConnection; 
import java.net.MalformedURLException; 
import java.net.URL; 
import android.app.Activity; 
import android.os.Bundle; 
import android.os.Environment; 
import android.os.Handler; 
import android.os.Message; 
import android.widget.ProgressBar; 
import android.widget.TextView; 
  
public class MulThreadDownload extends Activity { 
    /** Called when the activity is first created. */
    private ProgressBar pb1 = null; 
    private TextView tv1 = null; 
    private ProgressBar pb2 = null; 
    private TextView tv2 = null; 
  
    private String root = Environment.getExternalStorageDirectory() 
            .getAbsolutePath() + File.separator; 
    private String downloadFile = "http://www.android-study.com/resource/qzh.mp3"; 
    private String downloadFile1 = "http://www.android-study.com/resource/wk.mp3"; 
  
    // 声明已经读过的长度变量 
    private int hasRead = 0; 
  
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
  
        pb1 = (ProgressBar) findViewById(R.id.progressBar1); 
        tv1 = (TextView) findViewById(R.id.textView1); 
  
        pb2 = (ProgressBar) findViewById(R.id.progressBar2); 
        tv2 = (TextView) findViewById(R.id.textView2); 
  
        download(downloadFile, root, pb1, tv1); 
  
        download(downloadFile1, root, pb2, tv2); 
    } 
  
    private void download(String url, String targetPath, ProgressBar pb, 
            TextView tv) { 
        DownloadThread dt = new DownloadThread(url, targetPath, pb, tv); 
  
        dt.start(); 
    } 
  
    // 自定义一个Handler类，处理线程消息 
    public class MyHandler extends Handler { 
        private ProgressBar progressBar; 
        private TextView textView; 
  
        // 通过构造函数来确定给哪个ProgressBar刷新 
        public MyHandler(ProgressBar progressBar, TextView textView) { 
            this.progressBar = progressBar; 
            this.textView = textView; 
        } 
  
        public void handleMessage(Message msg) { 
            this.progressBar.setProgress(msg.arg1); 
            this.textView.setText(msg.arg1 + "%"); 
  
            super.handleMessage(msg); 
        } 
    } 
  
    // 下载线程 
    public class DownloadThread extends Thread { 
        private String url = ""; 
        private String targetPath = ""; 
  
        private int hasDownload = 0; 
  
        private int len = -1; 
        private byte buffer[] = new byte[4 * 1024]; 
        private int size = 0; 
        private int rate = 0; 
  
        private MyHandler myHandler = null; 
        private Message msg = null; 
  
        private ProgressBar pb = null; 
        private TextView tv = null; 
  
        public DownloadThread(String url, String targetPath, ProgressBar pb, 
                TextView tv) { 
            this.url = url; 
            this.targetPath = targetPath; 
  
            this.pb = pb; 
            this.tv = tv; 
  
            myHandler = new MyHandler(this.pb, this.tv); 
        } 
  
        public void run() { 
            String targetFileName = this.targetPath 
                    + this.url.substring(this.url.lastIndexOf("/") + 1, 
                            this.url.length()); 
            File downloadFile = new File(targetFileName); 
  
            if (!downloadFile.exists()) { 
                try { 
                    downloadFile.createNewFile(); 
                } catch (IOException e) { 
                    // TODO Auto-generated catch block 
                    e.printStackTrace(); 
                } 
            } 
  
            try { 
                URL fileUrl = new URL(this.url); 
                HttpURLConnection conn = (HttpURLConnection) fileUrl 
                        .openConnection(); 
  
                // 获取文件大小 
                size = conn.getContentLength(); 
  
                InputStream is = conn.getInputStream(); 
  
                OutputStream os = new FileOutputStream(targetFileName); 
  
                while ((len = is.read(buffer)) != -1) { 
                    os.write(buffer); 
  
                    hasDownload += len; 
  
                    rate = (hasDownload * 100 / size); 
  
                    msg = new Message(); 
  
                    msg.arg1 = rate; 
  
                    myHandler.sendMessage(msg); 
  
                    System.out.println(rate + "%"); 
                } 
            } catch (MalformedURLException e) { 
                // TODO Auto-generated catch block 
                e.printStackTrace(); 
            } catch (IOException e) { 
                e.printStackTrace(); 
            } 
  
        } 
    } 
  
}

程序运行效果：