swift 单例定义

方法一：

import Foundation

class SingleOne {

//单例
static let shareSingleOne = SingleOne()

}

方法二：

import Foundation

class SingleTwo {

//单例
class func shareSingleTwo()->SingleTwo{
struct Singleton{
static var oncetoken : dispatch_once_t = 0
static var single:SingleTwo?
}
dispatch_once(&Singleton.oncetoken,{
Singleton.single=shareSingleTwo()
}
)
return Singleton.single!
}

}

方法三：

import Foundation

//全局的常量
let single = SingleThree()

class SingleThree {

class var sharedInstance : SingleThree {
return single
}
}

方法四：

import Foundation class SingleFour { static var sharedInstance : SingleFour { struct Static { static let instance : SingleFour = SingleFour() } return Static.instance } }