如何从 Swift 中的 valueChanged 事件获取触摸坐标

背景

I've 以前学过的 https://stackoverflow.com/a/34764356/3681880如何使用手势识别器或continueTrackingWithTouch获取当前触摸位置的持续更新，然后使用它们执行如下操作：

然而现在，我想学习如何使用目标来做同样的事情。我已经可以通过使用来获得触地和触地事件TouchDown and TouchUpInside，但我不知道如何获得持续更新。我假设它将使用ValueChanged事件，但到目前为止还不起作用。

这是我尝试过的：

ViewController.swift

import UIKit
class ViewController: UIViewController {

    @IBOutlet weak var myCustomControl: MyCustomControl!
    @IBOutlet weak var trackingBeganLabel: UILabel!
    @IBOutlet weak var trackingEndedLabel: UILabel!
    @IBOutlet weak var xLabel: UILabel!
    @IBOutlet weak var yLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()

        // these work
        myCustomControl.addTarget(self, action: "myTouchDown", forControlEvents: UIControlEvents.TouchDown)
        myCustomControl.addTarget(self, action: "myTouchUpInside", forControlEvents: UIControlEvents.TouchUpInside)

        // this doesn't work
        myCustomControl.addTarget(self, action: "myValueChangedEvent:",
            forControlEvents: UIControlEvents.ValueChanged)
    }

    // this works
    func myTouchDown() {
        trackingBeganLabel.text = "Touched down"
    }

    // this works
    func myTouchUpInside() {
        trackingEndedLabel.text = "Touch up inside"
    }

    // this doesn't work, function never gets called
    func myValueChangedEvent(sender: UIControl) { 
        let location = sender.convertPoint(CGPointZero, toView: myCustomControl) 
        xLabel.text = "x: \(location.x)"
        yLabel.text = "y: \(location.y)"
    }
}

MyCustomControl.swift

import UIKit
class MyCustomControl: UIControl {
    // currently empty. Do I need to add something here?
}

Notes

• 得到@CaseyWagner的答案后更改了代码。编译器不再抛出错误，但是UIControlEvents.ValueChanged永远不会被解雇。
• 这个问题是我试图得到一个完整的答案方法一：添加目标的部分这个答案 https://stackoverflow.com/a/34764356/3681880.

Use UIControlEvents.TouchDragInside代替UIControlEvents.ValueChanged（另请注意，操作方法接收两个参数）：

myCustomControl.addTarget(self, action: "didDragInsideControl:withEvent:",
        forControlEvents: UIControlEvents.TouchDragInside)

处理函数如下所示：

func didDragInsideControl(control: MyCustomControl, withEvent event: UIEvent) {
    let touch = event.touchesForView(control)!.first!
    let location = touch.locationInView(control)
    xLabel.text = "x: \(location.x)"
    yLabel.text = "y: \(location.y)"
}