ios项目sb启动验证

//
//  AppDelegate.h
//

#import 
@interface AppDelegate : UIResponder 
@property (strong, nonatomic) UIWindow *window;
@end


//
//  AppDelegate.m
//  

#import "AppDelegate.h"
@implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSLog(@"application:%@",application);
    NSLog(@"AppDelegete:%@",self);
    NSLog(@"application.delegate:%@",application.delegate);
    NSLog(@"AppDelegete.window(self.window):%@",self.window);
    NSLog(@"application.windows:%@",application.windows);
    NSLog(@"application.keyWindow:%@",application.keyWindow);
    NSLog(@"AppDelegete.window.rootVC:%@",self.window.rootViewController);  
  
    return YES;
}

@end

//
//  ViewController.m
//

#import "ViewController.h"
@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"ViewController:%@",self);
}
@end

2017-02-18 21:23:24.137 WZMainController[2680:211019] application:
2017-02-18 21:23:24.137 WZMainController[2680:211019] AppDelegete:
2017-02-18 21:23:24.137 WZMainController[2680:211019] application.delegate:
2017-02-18 21:23:24.137 WZMainController[2680:211019] AppDelegete.window(self.window):

以上验证，通过sb启动，显示的window就是AppDelegate.h中的@property(strong)UIWindow *window; 而window.rootVC就是sb中绑定ViewController类的那个视图控制器。而application.keyWindow为null,因为UIApplication类的@property(nullable, nonatomic,readonly) UIWindow *keyWindow;可为空。故以后获取根控制器最可靠的方式是[UIApplication sharedApplication].windows[0];