IOS app starts

IOS app starts
1. main function 2. UIApplicationMain * Create UIApplication object * Create the delegate object of UIApplication 3. when the delegate object starts to process (Listen) system events (no storyboard is available) * after the program is started, the agent's application: didfinishlaunchingwitexceptions: Method * in application: didfinishlaunchingwitexceptions: create UIWindow * Create and set the rootViewController * display window of UIWindow 3. according to Info. plist to get the file name of the primary storyboard, load the primary storyboard (with storyboard) * Create UIWindow * Create and set the UIWindow rootViewController * display window