与目标c关联的对象存储进行交互

Question

我正在尝试创建一个实用程序，将闭包添加为UIControls的事件处理程序，尽管我遇到了一些问题，下面是代码：

public func addCallBack(callback: Void -> Void, forControlEvents events: UIControlEvents)
{   
    var optClosureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? Dictionary<UInt, Set<ClosureWrapper>>

    if optClosureDict == nil {
        optClosureDict = Dictionary<UInt, Set<ClosureWrapper>>()
    }

    var closureDict = optClosureDict!

    if closureDict[events.rawValue] == nil {
        closureDict[events.rawValue] = Set<ClosureWrapper>()
    }

    var closures = closureDict[events.rawValue]!

    let wrapper = ClosureWrapper(callback:callback)
    addTarget(wrapper, action:"invoked", forControlEvents: events)
    closures.insert(wrapper)

    objc_setAssociatedObject(self, &UIControlClosureDictKey, optClosureDict!, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
    var res = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? Dictionary<UInt, Set<ClosureWrapper>>
}

1)在调用返回可选API的情况下，这两个if语句看起来都很难看；如果它是零，我想用一些默认的方法覆盖它，那么我必须强制展开它。有没有一种更地道的“更快”的方法来做到这一点？

2)另外，当我创建一个包含一个键值对int到闭包的closureDict时，我使用setAssociatedObject存储它，然后在getAssociatedObject中检索回什么，我会得到一个带有0键值对的字典。怎么一回事？这是个问题，因为我的closureWrapper没有被保留，而且整个事情都不起作用

Answer 1

您可以简化行：

var optClosureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? Dictionary<UInt, Set<ClosureWrapper>>

if optClosureDict == nil {
    optClosureDict = Dictionary<UInt, Set<ClosureWrapper>>()
}

var closureDict = optClosureDict!

至

var closureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? Dictionary<UInt, Set<ClosureWrapper>> ?? Dictionary<UInt, Set<ClosureWrapper>>()

或者，您可以定义一个类型以使其更具可读性：

typealias ClosureDict = [UInt : Set<ClosureWrapper>]

然后这一行变成：

var closureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? ClosureDict ?? ClosureDict()

--

另外，下面的代码不符合您的要求：

var closures = closureDict[events.rawValue]!

let wrapper = ClosureWrapper(callback:callback)
addTarget(wrapper, action:"invoked", forControlEvents: events)
closures.insert(wrapper)

问题是Set是一个struct，与class不同，它不是一个“引用”类型。因此，var closures = ...行正在创建一个新的Set<ClosureWrapper>副本，而不是引用原始副本。因此，您正在更新Set<ClosureWrapper>的副本，而不是引用closureDict中的副本。

您可以在完成之后更新closureDict：

var closures = closureDict[events.rawValue]!

let wrapper = ClosureWrapper(callback:callback)
addTarget(wrapper, action:"invoked", forControlEvents: events)
closures.insert(wrapper)

closureDict[events.rawValue] = closures

或者更简单地，在原地更新它：

let wrapper = ClosureWrapper(callback:callback)
addTarget(wrapper, action:"invoked", forControlEvents: events)
closureDict[events.rawValue]!.insert(wrapper)

--

因此，这产生了以下备选方案：

func addCallBack(callback: Void -> Void, forControlEvents events: UIControlEvents) {
    var closureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? ClosureDict ?? ClosureDict()

    if closureDict[events.rawValue] == nil {
        closureDict[events.rawValue] = Set<ClosureWrapper>()
    }

    let wrapper = ClosureWrapper(callback:callback)
    addTarget(wrapper, action:"invoked", forControlEvents: events)
    closureDict[events.rawValue]!.insert(wrapper)

    objc_setAssociatedObject(self, &UIControlClosureDictKey, closureDict, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}

或

func addCallBack(callback: Void -> Void, forControlEvents events: UIControlEvents) {
    var closureDict = objc_getAssociatedObject(self, &UIControlClosureDictKey) as? ClosureDict ?? ClosureDict()

    var closures = closureDict[events.rawValue] ?? Set<ClosureWrapper>()

    let wrapper = ClosureWrapper(callback:callback)
    addTarget(wrapper, action:"invoked", forControlEvents: events)
    closures.insert(wrapper)

    closureDict[events.rawValue] = closures

    objc_setAssociatedObject(self, &UIControlClosureDictKey, closureDict, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}