在 Swift 中，您可以像这样为按钮创建一个函数：
button.addTarget(self, action: #selector(buttonAction), forControlEvents: .TouchUpInside)
但是有办法让我做这样的事情：
button.whenButtonIsClicked({Insert code here})
这样我什至没有为按钮声明一个显式函数。我知道我可以使用按钮标签，但我更愿意这样做。
【问题讨论】：
UIButton 的子类来做到这一点。
标签： swift button uibutton closures
创建您自己的UIButton 子类来执行此操作：
class MyButton: UIButton {
var action: (() -> Void)?
func whenButtonIsClicked(action: @escaping () -> Void) {
self.action = action
self.addTarget(self, action: #selector(MyButton.clicked), for: .touchUpInside)
}
// Button Event Handler:
// I have not marked this as @IBAction because it is not intended to
// be hooked up to Interface Builder
@objc func clicked() {
action?()
}
}
当您以编程方式创建按钮然后调用whenButtonIsClicked 来设置其功能时，将MyButton 替换为UIButton。
您也可以在 Storyboard 中将其与 UIButtons 一起使用（只需将其类更改为 MyButton），然后在 viewDidLoad 中调用 whenButtonIsClicked。
@IBOutlet weak var theButton: MyButton!
var count = 0
override func viewDidLoad() {
super.viewDidLoad()
// be sure to declare [unowned self] if you access
// properties or methods of the class so that you
// don't create a strong reference cycle
theButton.whenButtonIsClicked { [unowned self] in
self.count += 1
print("count = \(self.count)")
}
更强大的实现
认识到程序员可能想要处理的事件不仅仅是.touchUpInside，我编写了这个功能更强大的版本，它支持每个UIButton 的多个闭包和每个事件类型的多个闭包。
class ClosureButton: UIButton {
private var actions = [UInt : [((UIControl.Event) -> Void)]]()
private let funcDict: [UInt : Selector] = [
UIControl.Event.touchCancel.rawValue: #selector(eventTouchCancel),
UIControl.Event.touchDown.rawValue: #selector(eventTouchDown),
UIControl.Event.touchDownRepeat.rawValue: #selector(eventTouchDownRepeat),
UIControl.Event.touchUpInside.rawValue: #selector(eventTouchUpInside),
UIControl.Event.touchUpOutside.rawValue: #selector(eventTouchUpOutside),
UIControl.Event.touchDragEnter.rawValue: #selector(eventTouchDragEnter),
UIControl.Event.touchDragExit.rawValue: #selector(eventTouchDragExit),
UIControl.Event.touchDragInside.rawValue: #selector(eventTouchDragInside),
UIControl.Event.touchDragOutside.rawValue: #selector(eventTouchDragOutside)
]
func handle(events: [UIControl.Event], action: @escaping (UIControl.Event) -> Void) {
for event in events {
if var closures = actions[event.rawValue] {
closures.append(action)
actions[event.rawValue] = closures
} else {
guard let sel = funcDict[event.rawValue] else { continue }
self.addTarget(self, action: sel, for: event)
actions[event.rawValue] = [action]
}
}
}
private func callActions(for event: UIControl.Event) {
guard let actions = actions[event.rawValue] else { return }
for action in actions {
action(event)
}
}
@objc private func eventTouchCancel() { callActions(for: .touchCancel) }
@objc private func eventTouchDown() { callActions(for: .touchDown) }
@objc private func eventTouchDownRepeat() { callActions(for: .touchDownRepeat) }
@objc private func eventTouchUpInside() { callActions(for: .touchUpInside) }
@objc private func eventTouchUpOutside() { callActions(for: .touchUpOutside) }
@objc private func eventTouchDragEnter() { callActions(for: .touchDragEnter) }
@objc private func eventTouchDragExit() { callActions(for: .touchDragExit) }
@objc private func eventTouchDragInside() { callActions(for: .touchDragInside) }
@objc private func eventTouchDragOutside() { callActions(for: .touchDragOutside) }
}
演示
class ViewController: UIViewController {
var count = 0
override func viewDidLoad() {
super.viewDidLoad()
let button = ClosureButton(frame: CGRect(x: 50, y: 100, width: 60, height: 40))
button.setTitle("press me", for: .normal)
button.setTitleColor(.blue, for: .normal)
// Demonstration of handling a single UIControl.Event type.
// If your closure accesses self, be sure to declare [unowned self]
// to prevent a strong reference cycle
button.handle(events: [.touchUpInside]) { [unowned self] _ in
self.count += 1
print("count = \(self.count)")
}
// Define a second handler for touchUpInside:
button.handle(events: [.touchUpInside]) { _ in
print("I'll be called on touchUpInside too")
}
let manyEvents: [UIControl.Event] = [.touchCancel, .touchUpInside, .touchDown, .touchDownRepeat, .touchUpOutside, .touchDragEnter,
.touchDragExit, .touchDragInside, .touchDragOutside]
// Demonstration of handling multiple events
button.handle(events: manyEvents) { event in
switch event {
case .touchCancel:
print("touchCancel")
case .touchDown:
print("touchDown")
case .touchDownRepeat:
print("touchDownRepeat")
case .touchUpInside:
print("touchUpInside")
case .touchUpOutside:
print("touchUpOutside")
case .touchDragEnter:
print("touchDragEnter")
case .touchDragExit:
print("touchDragExit")
case .touchDragInside:
print("touchDragInside")
case .touchDragOutside:
print("touchDragOutside")
default:
break
}
}
self.view.addSubview(button)
}
}
【讨论】：
@IBAction修饰符而不是@objc，它会感觉更好的逻辑。
@IBAction 用于您要在 Interface Builder 中连接的功能。 @objc 用于选择器，所以即使@IBAction 包含@objc，我觉得@objc 在这里更合适，因为clicked 是一种内部方法，不打算通过IB 连接。
@IBAction 修饰符会向读者表明，实际方法在这里是一个真正的事件处理程序，而不是用于通用回调方法（例如通知、计时器等）的通用 @objc 修饰符
@IBAction，我相信我会收到有关如何将该方法连接到情节提要中的按钮的问题。
@IBAction 标记方法表示该方法是一个事件处理程序，并且不会仅标记代码和 IB 之间的排他连接;您可以将它仅用于这样的目的，但这并不普遍，您不能期望@IBAction自动只使用这样的用例。
这个会起作用的！ 确保不要更改按钮的标签
extension UIButton {
private func actionHandleBlock(action:(()->())? = nil) {
struct __ {
var closure : (() -> Void)?
typealias EmptyCallback = ()->()
static var action : [EmptyCallback] = []
}
if action != nil {
// __.action![(__.action?.count)!] = action!
self.tag = (__.action.count)
__.action.append(action!)
} else {
let exe = __.action[self.tag]
exe()
}
}
@objc private func triggerActionHandleBlock() {
self.actionHandleBlock()
}
func addAction(forControlEvents control :UIControlEvents, ForAction action:@escaping () -> Void) {
self.actionHandleBlock(action: action)
self.addTarget(self, action: #selector(triggerActionHandleBlock), for: control)
}
}
【讨论】：
let bt1 = UIButton(type: UIButtonType.InfoDark)
bt1.frame = CGRectMake(130, 80, 40, 40)
let bt2 = UIButton(type: UIButtonType.RoundedRect)
bt2.frame = CGRectMake(80, 180, 150, 44)
bt2.backgroundColor = UIColor.purpleColor()
bt2.tintColor = UIColor.yellowColor()
bt2.setTitle("Tap Me", forState: UIControlState.Normal)
bt2.addTarget(self, action: "buttonTap", forControlEvents: UIControlEvents.TouchUpInside)
let bt3 = UIButton(type: UIButtonType.RoundedRect)
bt3.backgroundColor = UIColor.brownColor()
bt3.tintColor = UIColor.redColor()
bt3.setTitle("Tap Me", forState: UIControlState.Normal)
bt3.frame = CGRectMake(80, 280, 150, 44)
bt3.layer.masksToBounds = true
bt3.layer.cornerRadius = 10
bt3.layer.borderColor = UIColor.lightGrayColor().CGColor
self.view.addSubview(bt1)
self.view.addSubview(bt2)
self.view.addSubview(bt3)
}
func buttonTap(button:UIButton)
{
let alert = UIAlertController(title: "Information", message: "UIButton Event", preferredStyle: UIAlertControllerStyle.Alert)
let OKAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: nil)
alert.addAction(OKAction)
}
【讨论】：
您也可以只继承 UIView 并拥有一个类似于 vacawama 的闭包属性。
var action: () -> ()?
然后重写touchesBegan 方法以在触摸按钮时调用该函数。使用这种方法虽然您不会获得从 UIBitton 开始的所有好处。
【讨论】：
如果您不想做任何“有问题的”事情（即，使用 Objective-C 的动态功能，或添加您自己的触摸处理程序等）并且纯粹在 Swift 中执行此操作，那么很遗憾，这是不可能的。
任何时候你在 Swift 中看到#selector，编译器都会在后台调用objc_MsgSend。 Swift 不支持 Objective-C 的动态性。无论好坏，这意味着为了将这个选择器的使用替换为一个块，您可能需要执行一些黑魔法才能使其工作，并且您必须使用 Objective-C 构造来这样做。
如果您对“令人讨厌的动态 Objective-C 东西”没有任何疑虑，您可以通过在 UIButton 上定义扩展来实现这一点，然后使用关联对象动态地将函数关联到对象。我将在此停止，但如果您想了解更多信息，NSHipster 有一个很棒的 overview 关于关联对象以及如何使用它们。
【讨论】：