//声明闭包
typealias valueBlock = (Float)->()
var returnPrice: valueBlock?
 
 
//调用该闭包
self.returnPrice?(price)

let sb = UIStoryboard(name:"Main", bundle: nil)
        
let vc = sb.instantiateViewControllerWithIdentifier("keypadViewVC") as! keypadViewVC
        
//B类的回调
vc.returnPrice = {price in self.gratuityBtn.setTitle(String(format: "%.2f", price), forState:UIControlState.Normal)}
        
self.presentViewController(vc, animated: true, completion: nil)