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

ios UIApplication简单使用