swift 的 guard & defer

移动组周技术分享

guard 使用

守卫，和隐式解析搭配有奇效

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// 原始方法 (强解包可能会出现问题)
func tranIntToString1(x: Int?) -> String {
    if x == nil || x! <= 0 {
  	    // 不符合值的要求时，写点代码
        return ""
    }
    // 使用x
    return x!.description
}
// 改进
func tranIntToString2(x: Int?) -> String {
    if let x = x where x>0 {
        return x.description
    }
    return ""
}
// 保镖模式
// 和上面写法对比
func tranIntToString3(x: Int?) -> String {
    guard let x = x where x > 0 else {
        return ""
    }
    // 变量不符合条件判断时，执行下面代码
    return x.description
}
// 非可选型
func tranIntToString4(x: Int) -> String {
    guard x > 0 else {
        return ""
    }
    return x.description
}
// 常常用于条件判断拦截
var view = UIView(frame: CGRectMake(0,0,80,80))
view.backgroundColor = UIColor.redColor()
UIView.animateWithDuration(0.3) { [weak view]() -> Void in
    guard let view = view where view.alpha>0 else {return}
    view.alpha = 0
}

懒加载

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//1.分析 NSArray 是一个闭包的返回值，而这是一个没有参数的闭包 
lazy var dataArray:NSArray = { [] }() 
//2.也可以写成这样 
lazy var dataArray:NSArray = { return NSArray() }()
//3.从plist文件加载 
lazy var dataArray:Array<XWWine> = {
    let winePath = NSBundle.mainBundle().pathForResource("wine.plist", ofType: nil)!
    let winesM = NSMutableArray(contentsOfFile: winePath);
    var tmpArray:Array<XWWine>! = []
    for tmpWineDict in winesM! {
        var wine:XWWine = XWWine.wineWithDict(tmpWineDict as! NSDictionary)
        tmpArray.append(wine)
    }
    //lazy闭包里就运行一次
    return tmpArray
}()

调用的时候再在家初始化方法（懒加载）

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lazy private var underlineView: UIView = {
    let view = UIView(frame: .zero)
    return view
}()

defer 关键字

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/*
    defer 关键字
*/
postfix func ++(inout x: Int) -> Int {
    defer {
        x = x/2
        defer {
            x += 100
        }
    }
    return x
}
//
//postfix func ++(inout x: Int) -> Int {
//    let current = x
//    x += 2
//    return current
//}
var num = 100
let num2 = num++
num		//150
num2	//100
prefix func ++(inout x:Int) -> Int {
    x += 2
    return x
}
var number = 100
let number2 = ++number
number 		// 102
number2		// 102

嵌套枚举使用(简直就是动态Model)

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public enum MenuScrollingMode {
    case ScrollEnabled
    case ScrollEnabledAndBouces
    case PagingEnabled
}
public enum MenuItemWidthMode {
    case Flexible
    case Fixed(width: CGFloat)
}
public enum MenuDisplayMode {
    case Standard(widthMode: MenuItemWidthMode, centerItem: Bool, scrollingMode: MenuScrollingMode)
    case SegmentedControl
    case Infinite(widthMode: MenuItemWidthMode)
}
// 初始化：用来携带信息很不错
public var menuDisplayMode = MenuDisplayMode.Standard(widthMode: PagingMenuOptions.MenuItemWidthMode.Fixed(width: 44), centerItem: false, scrollingMode: PagingMenuOptions.MenuScrollingMode.PagingEnabled)
// 实例
func labelWidth(size size: CGSize, widthMode: PagingMenuOptions.MenuItemWidthMode) -> CGFloat {
    switch widthMode {
    case .Flexible: return ceil(size.width)
    case let .Fixed(width): return width
    }
}