从swift与objective 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来添加闭包作为 UIControls 的事件处理程序，尽管我遇到了一些问题，这里是代码：

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) 两个 if 语句看起来都很难看，我调用了一个返回可选的 API，如果它是 nil，我想用一些默认值覆盖它，那么我必须强制解包它。有没有更惯用的“Swifter”方式来做到这一点？

2) 同样，当我创建一个具有一个 int 键值对的闭包字典时，我使用 setAssociatedObject 将其存储，然后我在 getAssociatedObject 中检索回来的内容，我得到一个包含 0 个键值对的字典。到底是怎么回事？这是一个问题，因为我的closureWrapper 没有被保留并且整个事情都没有工作

Answer 1

你可以简化线条：

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

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

var closureDict = optClosureDict!

到

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>]

然后那行变成：

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

--

另外，下面的代码并没有达到你的预期：

var closures = closureDict[events.rawValue]!

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

问题在于Set 是struct，与class 不同，它不是“引用”类型。所以var closures = ... 行正在制作Set<ClosureWrapper> 的新副本，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

或者更简单地说，就地更新它：

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

--

因此这会产生以下替代方案：

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)
}