- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    // Override point for customization after application launch.

    _navigationController=[[UINavigationController alloc]initWithRootViewController:[[UIViewController alloc] init]];

    _window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    _window.rootViewController = _navigationController;

    _window.backgroundColor = [UIColor redColor];

    [_window makeKeyAndVisible];

    return YES;

}

AppDelegate.h里加入

@property (strong,nonatomic)UINavigationController *navigationController;

iOS 9以后要设置rootviewcontroller

把你AppDelegate.m里写的UIwindow部分代码发来看看