项目需求,需要做一个下载功能，当然理想的功能要支持多任务同时下载，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
开始我的思路是在一个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。。。。。。
首先是布局文件,这个没什么,贴上代码：
main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ProgressBar
android:id="@+id/progressBar1"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
</ProgressBar>
<TextView
android:id="@+id/textView1"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<ProgressBar
android:id="@+id/progressBar2"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
</ProgressBar>
<TextView
android:id="@+id/textView2"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</LinearLayout>
然后是配置文件，上代码：
AndroidManifest.xml
<?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>
下面就是实现代码，代码中有相应的注释：
MulThreadDownload.java
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 final String root = Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator;
private final String downloadFile = "http://gongxue.cn/yingyinkuaiche/UploadFiles_9323/201008/2010082909434077.mp3";
private final String downloadFile1 = "http://gongxue.cn/yingyinkuaiche/UploadFiles_9323/201008/2010082909434077.mp3";
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main);
this.pb1 = (ProgressBar) this.findViewById(R.id.progressBar1);
this.tv1 = (TextView) this.findViewById(R.id.textView1);
this.pb2 = (ProgressBar) this.findViewById(R.id.progressBar2);
this.tv2 = (TextView) this.findViewById(R.id.textView2);
this.download(this.downloadFile, this.root, this.pb1, this.tv1);
this.download(this.downloadFile1, this.root, this.pb2, this.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 final ProgressBar progressBar;
private final 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 final 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;
this.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) {
e.printStackTrace();
}
}
try {
URL fileUrl = new URL(this.url);
HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();
// 获取文件大小
this.size = conn.getContentLength();
InputStream is = conn.getInputStream();
OutputStream os = new FileOutputStream(targetFileName);
while ((this.len = is.read(this.buffer)) != -1) {
os.write(this.buffer);
this.hasDownload += this.len;
this.rate = (this.hasDownload * 100 / this.size);
this.msg = new Message();
this.msg.arg1 = this.rate;
this.myHandler.sendMessage(this.msg);
System.out.println(this.rate + "%");
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
MyThreadTest.java
package sms.down;
import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ProgressBar;
import android.widget.TextView;
public class MyThreadTest extends Activity {
private ProgressBar pb1 = null;
private TextView tv1 = null;
private Handler handler = null;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.main);
this.pb1 = (ProgressBar) this.findViewById(R.id.progressBar1);
this.tv1 = (TextView) this.findViewById(R.id.textView1);
handler = new Handler() {
public void handleMessage(Message msg) {
pb1.setProgress(msg.arg1);
tv1.setText(msg.arg1 + "%");
switch (msg.arg1) {
case 100:
tv1.setText("下载完成!!");
break;
}
super.handleMessage(msg);
}
};
Runnable runnable = new Runnable() {
int i = 0;
public void run() {
while (i != 100) {
i = i + 10;
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
Message message = new Message();
message.arg1 = i;
handler.sendMessage(message);
}
}
};
new Thread(runnable).start();
}
}
下面上一张真机效果图：
源码下载地址：http://download.csdn.net/detail/gulaer/5004954 源码中包含"android 之断点续传详解三部曲之[二] → 断点续传下载"和"android 之断点续传详解三部曲之[三] → 多任务同时下载"代码.
原文地址：http://blog.csdn.net/shimiso/article/details/6763986 非常感谢原作者.
