UIApplication的作用--演示：

    - (void)viewDidLoad {

    [superviewDidLoad];

    UIApplication*app = [UIApplicationsharedApplication];

    UIUserNotificationSettings*settings = [UIUserNotificationSettingssettingsForTypes:UIUserNotificationTypeBadgecategories:nil];

      //注冊通知

     [appregisterUserNotificationSettings:settings];

     //1.設(shè)置應(yīng)用程序圖標(biāo)提醒數(shù)字

       app.applicationIconBadgeNumber=0;

     //2.設(shè)置聯(lián)網(wǎng)狀態(tài)

      app.networkActivityIndicatorVisible=YES;

      //3.設(shè)置狀態(tài)欄

      //在iOS7之后狀態(tài)欄都是交給控制器管理，不用下方的代碼了。

     app.statusBarHidden = YES;

       [app setStatusBarHidden:YES withAnimation:UIStatusBarAnimationSlide];

       //4.打電話,發(fā)短信,打開網(wǎng)頁.

       URL:資源唯一路徑

       //http://www.baidu.com

      //URL:協(xié)議頭//路徑//       http://

      //其實蘋果就是根據(jù)協(xié)議頭判斷用什么軟件去打開

      NSURL*url = [NSURLURLWithString:@"http://www.baidu.com"];

      [appopenURL:url];

        }

          //隱藏狀態(tài)欄

        -(BOOL)prefersStatusBarHidden

         {

         return YES;

           }