swift扩展Extension_011-swift延展基本使用

//: Playground - noun: a place where people can play

import UIKit

//----扩展Extension---------//
//作用：给已有的类、结构体、枚举扩展新的功能(方法和属性)
//Swift中的扩展没有名字 

//1.扩展属性：只能添加计算属性，不能添加存储属性
extension UIView {

    //var isSuperView = false

    var height : CGFloat {

          get {

            return self.frame.size.height

         }
        set {

            self.frame.size.height = newValue

        }

    }

}

var myView = UIView.init(frame: CGRectMake(100, 100, 100, 100))
myView.height = 200
print(myView.height)

//2.扩展方法

extension String {

    //字符串子串的截取
    func subStringFromStartIndexAndEndIndex(start : Int, end : Int) -> String {

        var count = 0
        var result = ""

        for char in self.characters {

            if count >= start {
                result += "\(char)"
            }

            if count >= end {
                break
            }

            count++

        }

        return result

    }

    //Bool转化为String
    static func stringWithBool(value : Bool) -> String {

        return "\(value)"
    }

}

var str = "Hello 88"
str.subStringFromStartIndexAndEndIndex(0, end: 4)
String.stringWithBool(true)