学习android快两个月了，一直坚持从迷茫中寻找可以得到的尽可能多的东西
想做一个下载功能，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。。。
package oneRain.MulThreadDownload; 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 oneRain.MulThreadDownload.DownloadServicer.DownloadThread; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.os.Environment; import android.os.Handler; import android.os.Looper; 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://192.168.1.5/android/test.zip"; private String downloadFile1 = "http://192.168.1.5/android/test1.exe"; //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; } //万恶的动词和名词 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(); } } } }
