每个app有且只有一个UIApplication对象，当程序启动的时候通过调用UIApplicationMain方法得到的。可以通过sharedApplication方法得到。

UIApplication对象的主要任务是处理用户事件的处理路径，例如分发一个UIEvent到另外一个对象去处理。UIApplication对象持有众多的UIWindow对象，因此可以组织app的展示。UIApplication对象还能处理一些资源，例如通过openURL:打开邮箱客户端或者设置界面等。

获得UIApplication对象

[UIApplication sharedApplication]

获得UIApplicationDelegate对象

[[UIApplication sharedApplication] delegate]

获得UIWindow对象

[[UIApplication sharedApplication] windows];   //UIWindow数组

[[UIApplication sharedApplication] keyWindow]; //UIWindow数组中最后调用makeKeyAndVisible方法的UIWindow对象

控制和处理UIEvent

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

{//分发一个event到另外一个对象去处理

    [[UIApplication sharedApplication] sendAction:@selector(action: forEvent:) to:[CustomHandler sharedCustomHandler] from:self forEvent:event];

}

[[UIApplication sharedApplication] beginIgnoringInteractionEvents]; //开始忽略Event

//...中间调用动画等操作

[[UIApplication sharedApplication] endIgnoringInteractionEvents];   //结束忽略Event

[UIApplication sharedApplication].applicationSupportsShakeToEdit = YES;  //晃动是否有撤销或者重做动作

打开URL资源

[[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];//打开设置界面

配置通知设置

UIUserNotificationType  types = UIUserNotificationTypeBadge | UIUserNotificationTypeSound | UIUserNotificationTypeAlert;

UIUserNotificationSettings  *mySettings  = [UIUserNotificationSettings settingsForTypes:types categories:nil];

[[UIApplication sharedApplication] registerUserNotificationSettings:mySettings]; //注册远程推送通知

[[UIApplication sharedApplication] registerForRemoteNotifications];//注册

[[UIApplication sharedApplication] unregisterForRemoteNotifications];//注销

    NSDate *date = [NSDate dateWithTimeIntervalSinceNow:10];

    UILocalNotification *localNotif = [[UILocalNotification alloc] init];

    localNotif.fireDate = date;  //时间

    localNotif.timeZone = [NSTimeZone localTimeZone]; //时区

    localNotif.repeatInterval = NSCalendarUnitMinute; //间隔

    localNotif.soundName = UILocalNotificationDefaultSoundName; //声音

    localNotif.alertBody = @"Local Test";   //通知内容

    localNotif.applicationIconBadgeNumber = 1;  //数字标示

    localNotif.userInfo = @{@"key":@"test"};    //info

    [[UIApplication sharedApplication] scheduleLocalNotification:localNotif]; //注册通知

    [[UIApplication sharedApplication] presentLocalNotificationNow:localNotif]; //立即通知

    [[UIApplication sharedApplication] cancelAllLocalNotifications]; //取消所有通知

    [[UIApplication sharedApplication] cancelLocalNotification:localNotif]; //取消特定的通知

    NSArray *arr = [[UIApplication sharedApplication] scheduledLocalNotifications];  //所有的通知

后台运行相关

    [[UIApplication sharedApplication] applicationState]; //app状态

    [[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:3600]; //设置后台运行时间

    NSTimeInterval remainTime = [[UIApplication sharedApplication] backgroundTimeRemaining]; //app后台运行的时间

    NSLog(@"remainTIme = %f",remainTime);

    int state = [[UIApplication sharedApplication] backgroundRefreshStatus]; //后台刷新的状态

    NSLog(@"state = %d",state);

    [[UIApplication sharedApplication] beginBackgroundTaskWithName:@"taskOne" expirationHandler:^{

    }];

    [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{

    }];

    [[UIApplication sharedApplication] endBackgroundTask:1];

远程的控制相关

    [[UIApplication sharedApplication] beginReceivingRemoteControlEvents];

    [[UIApplication sharedApplication] endReceivingRemoteControlEvents];

系统的Idle Timer

[UIApplication sharedApplication].idleTimerDisabled = YES; //不让手机休眠

APP样式

    //隐藏状态条

    [[UIApplication sharedApplication] setStatusBarHidden:YES];

    [[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation:UIStatusBarAnimationSlide];

    //设置状态条的样式

    [[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleDefault];

    [[UIApplication sharedApplication] statusBarStyle];

    //状态条的Frame

    [[UIApplication sharedApplication] statusBarFrame];

    //网络是否可见

    [[UIApplication sharedApplication] isNetworkActivityIndicatorVisible];

    //badge数字

    [UIApplication sharedApplication].applicationIconBadgeNumber = 2;

    //屏幕的方向

    [[UIApplication sharedApplication] userInterfaceLayoutDirection];

设置状态条的方向

[[UIApplication sharedApplication] setStatusBarOrientation:UIInterfaceOrientationLandscapeLeft animated:YES];

数据类型

UIBackgroundTaskIdentifier : Int

typedef enum : NSUInteger {

   UIRemoteNotificationTypeNone    = 0,

   UIRemoteNotificationTypeBadge   = 1 << 0,

   UIRemoteNotificationTypeSound   = 1 << 1,

   UIRemoteNotificationTypeAlert   = 1 << 2,

   UIRemoteNotificationTypeNewsstandContentAvailability = 1 << 3

} UIRemoteNotificationType;

typedef enum : NSInteger {

   UIStatusBarStyleDefault,

   UIStatusBarStyleLightContent,

   UIStatusBarStyleBlackTranslucent,

   UIStatusBarStyleBlackOpaque

} UIStatusBarStyle;

typedef enum : NSInteger {

   UIStatusBarAnimationNone,

   UIStatusBarAnimationFade,

   UIStatusBarAnimationSlide,

} UIStatusBarAnimation;

typedef enum : NSInteger  {

   UIApplicationStateActive ,

   UIApplicationStateInactive ,

   UIApplicationStateBackground

} UIApplicationState;

const UIBackgroundTaskIdentifier  UIBackgroundTaskInvalid ;

const NSTimeInterval  UIMinimumKeepAliveTimeout;

typedef enum : NSUInteger  {

   UIBackgroundFetchResultNewData ,

   UIBackgroundFetchResultNoData ,

   UIBackgroundFetchResultFailed

} UIBackgroundFetchResult;

const NSTimeInterval  UIApplicationBackgroundFetchIntervalMinimum ;

const NSTimeInterval  UIApplicationBackgroundFetchIntervalNever;

typedef enum : NSUInteger  {

   UIBackgroundRefreshStatusRestricted ,

   UIBackgroundRefreshStatusDenied ,

   UIBackgroundRefreshStatusAvailable

} UIBackgroundRefreshStatus;

typedef enum : NSInteger  {

   UIInterfaceOrientationUnknown             = UIDeviceOrientationUnknown ,

   UIInterfaceOrientationPortrait            = UIDeviceOrientationPortrait ,

   UIInterfaceOrientationPortraitUpsideDown  = UIDeviceOrientationPortraitUpsideDown ,

   UIInterfaceOrientationLandscapeLeft       = UIDeviceOrientationLandscapeRight ,

   UIInterfaceOrientationLandscapeRight      = UIDeviceOrientationLandscapeLeft

} UIInterfaceOrientation;

typedef enum : NSInteger  {

   UIUserInterfaceLayoutDirectionLeftToRight ,

   UIUserInterfaceLayoutDirectionRightToLeft ,

} UIUserInterfaceLayoutDirection;

NSString *const  UIApplicationOpenSettingsURLString;

NSString *const  UIApplicationStatusBarOrientationUserInfoKey ;

NSString *const  UIApplicationStatusBarFrameUserInfoKey;

NSString *const  UIContentSizeCategoryExtraSmall ;

NSString *const  UIContentSizeCategorySmall ;

NSString *const  UIContentSizeCategoryMedium ;

NSString *const  UIContentSizeCategoryLarge ;

NSString *const  UIContentSizeCategoryExtraLarge ;

NSString *const  UIContentSizeCategoryExtraExtraLarge ;

NSString *const  UIContentSizeCategoryExtraExtraExtraLarge;

NSString *const  UIContentSizeCategoryAccessibilityMedium ;

NSString *const  UIContentSizeCategoryAccessibilityLarge ;

NSString *const  UIContentSizeCategoryAccessibilityExtraLarge ;

NSString *const  UIContentSizeCategoryAccessibilityExtraExtraLarge ;

NSString *const  UIContentSizeCategoryAccessibilityExtraExtraExtraLarge;

NSString *const  UIApplicationInvalidInterfaceOrientationException;

通知

UIApplicationBackgroundRefreshStatusDidChangeNotification

UIApplicationDidBecomeActiveNotification

UIApplicationDidChangeStatusBarFrameNotification

UIApplicationDidChangeStatusBarOrientationNotification

UIApplicationDidEnterBackgroundNotification

UIApplicationDidFinishLaunchingNotification

UIApplicationDidReceiveMemoryWarningNotification

UIApplicationProtectedDataDidBecomeAvailable

UIApplicationProtectedDataWillBecomeUnavailable

UIApplicationSignificantTimeChangeNotification

UIApplicationUserDidTakeScreenshotNotification

UIApplicationWillChangeStatusBarOrientationNotification

UIApplicationWillChangeStatusBarFrameNotification

UIApplicationWillEnterForegroundNotification

UIApplicationWillResignActiveNotification

UIApplicationWillTerminateNotification

UIContentSizeCategoryDidChangeNotification