在我的ViewController的viewDidLoad中，我添加了一个按钮:lettutorialButton=UIButton.buttonWithType(UIButtonType.System)as!UIButtontutorialButton.frame=CGRectMake(0,(UIScreen.mainScreen().bounds.size.height/4)*3,UIScreen.mainScreen().bounds.size.width,20)tutorialButton.titleLabel?.textAlignment=NSTextAlignment.Ce