查看蘋果官方開(kāi)發(fā)文檔會(huì)發(fā)現(xiàn)NSView有兩個(gè)方法鼠標(biāo)進(jìn)入mouseEntered(with:)和鼠標(biāo)退出mouseExited(with:)兩個(gè)方法脱衙；
雖然文檔上說(shuō)：子類覆寫這兩個(gè)方法可以接受到對(duì)應(yīng)的事件侥猬；但實(shí)際上還需要override updateTrackingAreas方法并且更新對(duì)應(yīng)的trackingAreas

具體實(shí)現(xiàn)的代碼如下

class MouseTrackingView: NSView {
    var isMouseInside: Bool = false {
        didSet {
            print("isMouseInside:\(isMouseInside)")
        }
    }
    
    override func mouseExited(with event: NSEvent) {
        isMouseInside = false
    }
    
    override func mouseEntered(with event: NSEvent) {
        isMouseInside = true
    }
    
    override func updateTrackingAreas() {
        trackingAreas.forEach(removeTrackingArea(_:))
        addTrackingArea(.init(rect: .zero,
                              options: [.activeAlways, .inVisibleRect, .mouseEnteredAndExited],
                              owner: self,
                              userInfo: nil))
    }
}

實(shí)現(xiàn)懸停的邏輯是鼠標(biāo)進(jìn)入時(shí)改變按鈕樣式或者展示氣泡；鼠標(biāo)退出時(shí)恢復(fù)樣式或者氣泡消失捐韩；
為了實(shí)現(xiàn)視圖跟業(yè)務(wù)邏輯代碼分離需要定義一個(gè)鼠標(biāo)移動(dòng)事件退唠；
定義一個(gè)MouseMoveEvent的枚舉類型；并且增加subscribeMouseMoveEvent的事件訂閱方法便可將業(yè)務(wù)代碼和UI視圖的代碼分離開(kāi)來(lái)荤胁；具體實(shí)現(xiàn)如下

class MouseTrackingView: NSView {
    enum MouseMoveEvent {
        case exited, entered
    }
    
    typealias MouseMoveEventObserver = (MouseMoveEvent) -> Void
    
    private var observer: MouseMoveEventObserver?
    
    var mouseMoveEvent: MouseMoveEvent = .exited {
        didSet {
            observer?(mouseMoveEvent)
        }
    }
    
    override func mouseExited(with event: NSEvent) {
        mouseMoveEvent = .exited
    }
    
    override func mouseEntered(with event: NSEvent) {
        mouseMoveEvent = .entered
    }
    
    override func updateTrackingAreas() {
        trackingAreas.forEach(removeTrackingArea(_:))
        addTrackingArea(.init(rect: .zero,
                              options: [.activeAlways, .inVisibleRect, .mouseEnteredAndExited],
                              owner: self,
                              userInfo: nil))
    }
    
    func subscribeMouseMoveEvent(_ observer: MouseMoveEventObserver?) {
        self.observer = observer
    }
}

使用方法：

        @IBOutlet weak var mouseView: MouseTrackingView!

        mouseView.subscribeMouseMoveEvent { event in
            print("mouse event: \(event)")
            switch event {
            case .exited: break
            case .entered: break
            }
        }

到目前為止鼠標(biāo)懸停的目的已經(jīng)達(dá)到了铜邮；但是有一個(gè)小問(wèn)題：假設(shè)項(xiàng)目中有需求對(duì)NSTextField、NSView寨蹋、NSButton等等控件都需要實(shí)現(xiàn)鼠標(biāo)懸停的功能；那按照上面的方法就需要子類化所有控件扔茅、MouseMovableTextFiled已旧、MouseMovableView、MouseMovableButton; 顯然這樣做會(huì)出現(xiàn)大量重復(fù)的模版代碼召娜；

使用協(xié)議實(shí)現(xiàn)鼠標(biāo)懸停接口

如果可以定義一個(gè)協(xié)議MouseTrackable來(lái)實(shí)現(xiàn)鼠標(biāo)懸停的接口运褪；那么只要實(shí)現(xiàn)此協(xié)議的控件就能獲得鼠標(biāo)懸停的能力extension NSView: MouseTrackable {} ；代碼實(shí)現(xiàn)如下

import AppKit

enum MouseMoveEvent {
    case exited, entered
}

// MARK: -
protocol MouseTrackable {
    func subscribeMouseMoveEvent(_ observer: @escaping (MouseMoveEvent) -> Void)
}

// MARK: -
protocol MouseTrackCompatible {
    var mouseTracker: MouseTrackable { get }
}

// MARK: -
class MouseTracker: MouseTrackable {
    typealias MouseMoveEventObserver = (MouseMoveEvent) -> Void
    private var observer: MouseMoveEventObserver?
    
    private var event: MouseMoveEvent = .exited {
        didSet {
            observer?(event)
        }
    }
    
    func subscribeMouseMoveEvent(_ observer: @escaping MouseMoveEventObserver) {
        self.observer = observer
    }
    
    func updateMouseMoveEvent(_ event: MouseMoveEvent) {
        self.event = event
    }
}

// MARK: -
extension NSView: MouseTrackCompatible  {
    static var _mouseTracker: Int = 0
    var mouseTracker: MouseTrackable {
        guard let tracker = objc_getAssociatedObject(self, &Self._mouseTracker) as? MouseTracker else {
            let tracker = MouseTracker()
            objc_setAssociatedObject(self, &Self._mouseTracker, tracker, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
            exchangeUpdateTrackingAreasImplementation()
            return tracker
        }
        return tracker
    }
    
    open override func mouseExited(with event: NSEvent) {
        (mouseTracker as? MouseTracker)?.updateMouseMoveEvent(.exited)
    }
    
    open override func mouseEntered(with event: NSEvent) {
        (mouseTracker as? MouseTracker)?.updateMouseMoveEvent(.entered)
    }
   
    private func exchangeUpdateTrackingAreasImplementation() {
        let classObj = Self.self
        let origin = class_getInstanceMethod(classObj, #selector(updateTrackingAreas))!
        let new = class_getInstanceMethod(classObj, #selector(swizzle_updateTrackingAreas))!
        method_exchangeImplementations(origin, new)
    }
    
    @objc
    private func swizzle_updateTrackingAreas() {
        swizzle_updateTrackingAreas()
        trackingAreas.forEach(removeTrackingArea(_:))
        addTrackingArea(.init(rect: .zero,
                              options: [.activeAlways, .inVisibleRect, .mouseEnteredAndExited],
                              owner: self,
                              userInfo: nil))
    }
}

使用方法：

      self.label
         .mouseTracker
        .subscribeMouseMoveEvent { event in
            print("mouse event: \(event)")
            switch event {
            case .exited: break
            case .entered: break
            }
        }

使用協(xié)議實(shí)現(xiàn)鼠標(biāo)懸停接口的好處就是不用對(duì)目標(biāo)控件進(jìn)行子類化玖瘸；通過(guò)對(duì)NSView拓展出mouseTracker對(duì)象后便可以簡(jiǎn)單的實(shí)現(xiàn)鼠標(biāo)移動(dòng)事件的訂閱秸讹；當(dāng)然NSButton、NSImageView捕捂、NSTextField也會(huì)自動(dòng)繼承這個(gè)屬性方法广匙；

源代碼：
https://github.com/jifucao/ViewHover