其主要原理是：

在应用程序启动，取server在版本 ，

以下这个是获取当前应用的版本号信息

private void getCurVersion() {        try {            PackageInfo pInfo = context.getPackageManager().getPackageInfo(                    context.getPackageName(), 0);            curVersion = pInfo.versionName;            curVersionCode = pInfo.versionCode;        } catch (NameNotFoundException e) {            Log.e("update", e.getMessage());            curVersion = "1.0.1";            curVersionCode = 1;        }    }

以下则是通过java net包来get版本号信息。进行比較

server端格式例如以下     version_1.0.2

HttpURLConnection 获取输入流。再用

BufferedReader 缓冲流。readline成String，再比較

private boolean check_update(){		String getstring = null;		String version=null;		getCurVersion();		try {						URL myurl=new URL(app_check);						HttpURLConnection urlconnection=(HttpURLConnection) myurl.openConnection();			urlconnection.setReadTimeout(50000);			urlconnection.setConnectTimeout(50000);			urlconnection.connect();			InputStream in=urlconnection.getInputStream();						   BufferedReader buffread;			   buffread=new BufferedReader(new InputStreamReader(in,"utf-8"));			   String line;				line=buffread.readLine();				while(line!=null){					getstring+=line;					line=buffread.readLine();									}				int index=getstring.indexOf("version_");				//2.0.1				version=getstring.substring(index+8, index+13);				in.close();				Log.e("version",version);		} catch (MalformedURLException e) {			// TODO Auto-generated catch block			e.printStackTrace();		} catch (IOException e) {			// TODO Auto-generated catch block			e.printStackTrace();		}	    if(version!=null){		if(version.compareTo(curVersion)>0)			return true;		else			return false;	    }	    else	    	return false;	}

接下来则是弹出一对话框以及调用下载线程

private void showdownDialog(){		 AlertDialog.Builder dialog = new AlertDialog.Builder(context);  	        dialog.setTitle("软件版本号更新");  	        dialog.setMessage("有最新的app更新");  	       dialog.setNegativeButton("以后再说", new OnClickListener(){			@Override			public void onClick(DialogInterface arg0, int arg1) {				// TODO Auto-generated method stub				arg0.dismiss();			}	       	       });	       dialog.setPositiveButton("确定", new OnClickListener(){			@Override			public void onClick(DialogInterface dialog, int which) {				// TODO Auto-generated method stub				//确定里面调用下载线程，同一时候显示下载的那个进度对话框				dialog.dismiss();				cancel=true;				downapk();				showDownapk();			}	    	   	       });	       dialog.show();	}

最后则是发出一个Intent广播

private void setInstall(){

File apkfile = new File(apk_path);  

       if (!apkfile.exists()) {  

           return;  

       }      

       Intent i = new Intent(Intent.ACTION_VIEW);  

       i.setDataAndType(Uri.parse("file://" + apkfile.toString()), "application/vnd.android.package-archive");   

       context.startActivity(i); 

}

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