创建控制器的几种方式

    // bundle:nil参数传nil，指的是从mainbundle中加载，mainbundle中包含项目中所有的资源
    MJThreeViewController *three = [[MJThreeViewController alloc] initWithNibName:@"MJThree5345" bundle:nil];
    self.window.rootViewController = three;

// 根据代码创建控制器
    UIViewController *vc = [[UIViewController alloc]init];
    vc.view.backgroundColor = [UIColor blueColor];
    self.window.rootViewController = vc;

// 根据storyboard创建控制器
    UIStoryboard *board = [UIStoryboard storyboardWithName:@"one" bundle:nil];
    UIViewController *vc = [board instantiateViewControllerWithIdentifier:@"myredview"];
    self.window.rootViewController = vc;