ios UIApplication is simple to use

1, a program has only one UIApplication

//Obtain
UIApplication *app = [UIApplication sharedApplication];

// get error
UIApplication *app = [[UIApplication alloc] init];
//UIApplication is a singleton, if you try to create a new UIApplication object in the program, it will prompt an error

2. Using the obtained UIApplication, you can perform some application-level operations (reminder box of the app icon, display the networking status, make a call, open a web page, control the status bar )

//The reminder box of the app icon (the little red dot with information on the icon)
app.applocationIconBadgeNumber = 10; //10 is the reminder number

//To implement the above method, user notification must be registered:

//create user notification
UIUserNotificationSettings *settings = [UIUserNotificationSettings settingsForTypes:UIUserNotificationTypeBadge categories:nil];
//Notification for registered users
[app registerUserNotificationSettings: settings];

//Set the network status
app.networkActivityIndicatorVisible = YES;

//open the Web page
NSURL *url = [NSURL URLWithString: @"http://www.baidu.com"];
[[UIApplication sharedApplication] openURL: url];

//Protocol header: http, https, file, tel

//control the status bar

//After ios7, the status bar is determined by the controller by default, so:

// (1) When the View controller-based status bar appearance of the info.plist file is set to NO, the control of the status bar in the controller will be invalid

// hide the status bar
[app setStatusBarHidden: YES];
  
//Set the font color mode of the status bar
[app setStatusBarStyle:UIStatusBarStyleLightContent];

//Set the animation to hide the status bar
[app setStatusBarHidden: YES withAnimation: UIStatusBarAnimationSlide];





// (2) When the View controller-based status bar appearance of the info.plist file is set to YES, the UIApplication modification control bar is invalid, and a method needs to be added in the controller (ViewController)

//whether to hide the status bar
- (BOOL)prefersStatusBarHidden {
          return YES;
}
//Set the status bar font color
- (UIStatusBarStyle)preferredStatusBarStyle {
          return UIStatusBarStyleLightContent;
}

3,UIApplicationDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
       //Called when the program is started
}

- (void)applicationWillResignActive:(UIApplication *)application {
       //Called when the program loses focus means that it cannot interact with the user
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
       //Called when the program enters the background
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
       //Called when the program is about to enter the foreground
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
       //Called when the program gets the focus to interact with the user
}

- (void)applicationWillTerminate:(UIApplication *)application {
       //Calling this method when the program is closed cannot be verified
}

- (void)applicationDidReceiveMemoryWarning:(UIApplication *)application
{
       //Called when the program receives a memory warning
}


/*
When the program runs, the calling sequence is:
     1  application:didFinishLaunchingWithOptions:
     2  applicationDidBecomeActive:
Enter the program first, and then get the focus. At this time, the user can perform interactive operations such as clicking
*/

/*
Press the Home button:
     1  applicationWillResignActive:
     2  applicationDidEnterBackground:
First lose focus, can't interact, and then the program enters the background
*/

/*
Enter the program again:
     1  applicationWillEnterForeground:
     2  applicationDidBecomeActive:
First call the method about to enter the foreground, and then enter the program to get the focus
*/

ios UIApplication is simple to use

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