<TextView
  android:id="@+id/tv_splash_version"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:textColor="#000000"
  android:textStyle="bold"
  android:shadowDx="1"//阴影的偏移量
  android:shadowDy="1"
  android:shadowRadius="0.2"//阴影的半径
  android:shadowColor="#ffff00"
  android:text="版本：1.0"
  android:textSize="16sp"
  android:layout_centerInParent="true"/>

public String getAppVersion(){
  PackageManager pm = getPackageManager();
  try {
    PackageInfo info = pm.getPackageInfo(getPackageName(), 0);
    return info.versionName;
  } catch (NameNotFoundException e) {
    e.printStackTrace();
    //不可能发生；
    return "";
  }
}

protected void showUpdateDialog() {
 AlertDialog.Builder build = new Builder(this);
 build.setTitle("发现新版本");
 build.setMessage(description);
 build.setNegativeButton("立刻升级", new OnClickListener() {

   @Override
   public void onClick(DialogInterface dialog, int which) {
     //升级的代码；
   };
 });
 build.setPositiveButton("下次再说", new OnClickListener() {

   @Override
   public void onClick(DialogInterface dialog, int which) {
     dialog.dismiss();
 enterHome();

   }
 });
 build.show();

private void checkup() {
 new Thread() {
   public void run() {
     Message msg = Message.obtain();
     long startTime = System.currentTimeMillis();//启动该线程的系统时间
     try {
       //请求网络的代码
       URL url = new URL(getString(R.string.serverurl));
       HttpURLConnection conn = (HttpURLConnection) url
           .openConnection();
       conn.setRequestMethod("GET");//请求方法
       conn.setConnectTimeout(4000);//超时时间
       int code = conn.getResponseCode();//返回码200请求成功
       if (code == 200) {
         InputStream is = conn.getInputStream();
         String result = StreamTools.readFromStream(is);
         Log.i(TAG, "联网成功" + result);
         JSONObject obj = new JSONObject(result);//解析json字符串
         String version = (String) obj.get("version");//版本信息
         description = (String) obj.get("description");//描述信息
         apkurl = (String) obj.get("apkurl");
         if (getAppVersion().equals(version)) {
           msg.what = ENTER_HOME;
         } else {
           msg.what = SHOW_UPDATE_DIALOG;

         }
       }
     } catch (MalformedURLException e) {

       e.printStackTrace();
       msg.what = URL_ERROR;
     } catch (IOException e) {
       e.printStackTrace();
       msg.what = NETWORK_ERROR;
     } catch (JSONException e) {
       e.printStackTrace();
       msg.what = JSON_ERROR;
     } finally {
       handler.sendMessage(msg);
       long endTime = System.currentTimeMillis();//该线程执行完毕的时间
       long dTime = endTime-startTime;//该线程的阻塞时间
       if (dTime<3000) {
         try {
           Thread.sleep(3000-dTime);//若该线程的阻塞时间小于三秒继续睡眠到三秒
         } catch (InterruptedException e) {              
           e.printStackTrace();
         }
       }
     }
   }
 }.start();

 }
handler

 private Handler handler = new Handler() {

 @Override
 public void handleMessage(Message msg) {
   // TODO Auto-generated method stub
   super.handleMessage(msg);
   switch (msg.what) {
   case SHOW_UPDATE_DIALOG:
     showUpdateDialog();
     break;
   case ENTER_HOME:
     Toast.makeText(getApplicationContext(), "", 0).show();
     enterhome();
     break;
   case URL_ERROR:
     Toast.makeText(getApplicationContext(), "URL_ERROR", 0).show();
     enterhome();
     break;
   case NETWORK_ERROR:
     Toast.makeText(getApplicationContext(), "NETWORK_ERROR", 0).show();
     enterhome();
     break;

   case JSON_ERROR:
     Toast.makeText(getApplicationContext(), "JSON_ERROR", 0).show();
     enterhome();
     break;
   }
 }
};

  if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
      FinalHttp finalHttp = new FinalHttp();
        finalHttp.download(apkurl,Environment.getExternalStorageDirectory().getAbsolutePath()+
         "/mobilesafe2.0.apk" , new AjaxCallBack<File>() {

          @Override
          public void onLoading(long count, long current) {
            super.onLoading(count, current);
            tv_uapdate_info.setVisibility(View.VISIBLE);
            int progress =(int) (current*100/count);
                tv_uapdate_info.setText("下载进度："+progress+"%");
          }

          @Override
          public void onFailure(Throwable t, int errorNo,
              String strMsg) {
            t.printStackTrace();
            Toast.makeText(getApplicationContext(), "下载失败", 0).show();
            enterhome();

            super.onFailure(t, errorNo, strMsg);
          }

          @Override
          public void onSuccess(File t) {

            super.onSuccess(t);
            installAPK(t);

          }

          private void installAPK(File t) {
            Intent intent = new Intent();//自动安装程序可调用该段代码
            intent.setAction("android.intent.action.VIEW");
            intent.addCategory("android.intent.category.DEFAULT");
            intent.setDataAndType(Uri.fromFile(t), "application/vnd.android.package-archive");
            startActivity(intent);            
          }

        });

      }else{
        Toast.makeText(getApplicationContext(), "请插入内存卡再试",0).show();
        return;

      }

public class WelcomeActivity extends Activity  
{ 
  //定义一个handler,用来接收延迟发送的信息-启动activity 
  private Handler handler = new Handler() 
  { 
    @Override 
    <span style="color: #ff0000;">public void handleMessage(Message msg) </span> 
    { 
      // TODO Auto-generated method stub 
      super.handleMessage(msg); 
      switch(msg.what) 
      { 
      case 0x123: 
        Intent intent = new Intent(WelcomeActivity.this,  
            OnlineExamActivity.class); 
        startActivity(intent); 
        finish(); 
      } 
    } 
  }; 

@Override 
  protected void onCreate(Bundle savedInstanceState) 
  { 
    // TODO Auto-generated method stub 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.welcome_activity); 
    start(); 
  } 
 
  private void start()  
  { 
    <span style="color: #ff0000;">handler.sendEmptyMessageDelayed(0x123, 3000);</span> 
  }