android实现软件自动更新的步骤

package lgx.acc.updatedemo; 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.InputStream; 
import java.net.HttpURLConnection; 
import java.net.URL; 
import android.app.AlertDialog; 
import android.content.Context; 
import android.content.DialogInterface; 
import android.content.Intent; 
import android.net.Uri; 
import android.os.Handler; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.widget.ProgressBar; 
import android.widget.TextView; 
public class UpdateManager { 
 // 应用程序Context 
 private Context mContext; 
 // 是否是最新的应用,默认为false 
 private boolean isNew = false; 
 private boolean intercept = false; 
 // 下载安装包的网络路径 
 private String apkUrl = "http://shouji.360tpcdn.com/360sj/tpi/20130201/" 
   + "com.flikie.wallpapers.gallery_4.apk"; 
 // 保存APK的文件夹 
 private static final String savePath = "/sdcard/updatedemo/"; 
 private static final String saveFileName = savePath 
   + "UpdateDemoRelease.apk"; 
 // 下载线程 
 private Thread downLoadThread; 
 private int progress;// 当前进度 
 TextView text; 
 // 进度条与通知UI刷新的handler和msg常量 
 private ProgressBar mProgress; 
 private static final int DOWN_UPDATE = 1; 
 private static final int DOWN_OVER = 2; 
 public UpdateManager(Context context) { 
  mContext = context; 
 } 
 /** 
  * 检查是否更新的内容 
  */ 
 public void checkUpdateInfo() { 
  //这里的isNew本来是要从服务器获取的，我在这里先假设他需要更新 
  if (isNew) { 
   return; 
  } else { 
   showUpdateDialog(); 
  } 
 } 
 /** 
  * 显示更新程序对话框，供主程序调用 
  */ 
 private void showUpdateDialog() { 
  AlertDialog.Builder builder = new AlertDialog.Builder(mContext); 
  builder.setTitle("软件版本更新"); 
  builder.setMessage("有最新的软件包，请下载!"); 
  builder.setPositiveButton("下载", new DialogInterface.OnClickListener() { 
   @Override 
   public void onClick(DialogInterface dialog, int which) { 
    showDownloadDialog(); 
   } 
  }); 
  builder.setNegativeButton("以后再说", 
    new DialogInterface.OnClickListener() { 
     @Override 
     public void onClick(DialogInterface dialog, int which) { 
      dialog.dismiss(); 
     } 
    }); 
  builder.create().show(); 
 } 
 /** 
  * 显示下载进度的对话框 
  */ 
 private void showDownloadDialog() { 
  AlertDialog.Builder builder = new AlertDialog.Builder(mContext); 
  builder.setTitle("软件版本更新"); 
  LayoutInflater inflater = LayoutInflater.from(mContext); 
  View v = inflater.inflate(R.layout.progress, null); 
  mProgress = (ProgressBar) v.findViewById(R.id.progress); 
  builder.setView(v); 
  builder.setNegativeButton("取消", new DialogInterface.OnClickListener() { 
   @Override 
   public void onClick(DialogInterface dialog, int which) { 
    intercept = true; 
   } 
  }); 
  builder.show(); 
  downloadApk(); 
 } 
 /** 
  * 从服务器下载APK安装包 
  */ 
 private void downloadApk() { 
  downLoadThread = new Thread(mdownApkRunnable); 
  downLoadThread.start(); 
 } 
 private Runnable mdownApkRunnable = new Runnable() { 
  @Override 
  public void run() { 
   URL url; 
   try { 
    url = new URL(apkUrl); 
    HttpURLConnection conn = (HttpURLConnection) url 
      .openConnection(); 
    conn.connect(); 
    int length = conn.getContentLength(); 
    InputStream ins = conn.getInputStream(); 
    File file = new File(savePath); 
    if (!file.exists()) { 
     file.mkdir(); 
    } 
    File apkFile = new File(saveFileName); 
    FileOutputStream fos = new FileOutputStream(apkFile); 
    int count = 0; 
    byte[] buf = new byte[1024]; 
    while (!intercept) { 
     int numread = ins.read(buf); 
     count += numread; 
     progress = (int) (((float) count / length) * 100); 
     // 下载进度 
     mHandler.sendEmptyMessage(DOWN_UPDATE); 
     if (numread <= 0) { 
      // 下载完成通知安装 
      mHandler.sendEmptyMessage(DOWN_OVER); 
      break; 
     } 
     fos.write(buf, 0, numread); 
    } 
    fos.close(); 
    ins.close(); 
   } catch (Exception e) { 
    e.printStackTrace(); 
   } 
  } 
 }; 
 /** 
  * 安装APK内容 
  */ 
 private void installAPK() { 
  File apkFile = new File(saveFileName); 
  if (!apkFile.exists()) { 
   return; 
  } 
  Intent intent = new Intent(Intent.ACTION_VIEW); 
  intent.setDataAndType(Uri.parse("file://" + apkFile.toString()), 
    "application/vnd.android.package-archive"); 
  mContext.startActivity(intent); 
 }; 
 private Handler mHandler = new Handler() { 
  public void handleMessage(android.os.Message msg) { 
   switch (msg.what) { 
   case DOWN_UPDATE: 
    mProgress.setProgress(progress); 
    break; 
   case DOWN_OVER: 
    installAPK(); 
    break; 
   default: 
    break; 
   } 
  } 
 }; 
} 

<?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" > 
 <ProgressBar 
  android:id="@+id/progress" 
  style="?android:attr/progressBarStyleHorizontal" 
  android:layout_width="fill_parent" 
  android:layout_height="wrap_content" /> 
</LinearLayout> 

UpdateManager manager=new UpdateManager(MainActivity.this); 
  manager.checkUpdateInfo(); 

<uses-permission android:name="android.permission.INTERNET"/> 
 <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>