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"/