CAShapeLayer奇怪的動畫行為

Question

我正在嘗試創建一個動畫，其中當用戶拖動UIView時淡出兩行，而當用戶釋放拖動時淡出兩行。
因此，我有兩個函數undrawLines （在平移手勢開始時調用）和redrawLines （在平移手勢結束時調用），這些函數由我的UIPanGestureRecognizer操作處理程序調用。

func undrawLines() {

    line1.opacity = 0.0
    line2.opacity = 0.0

    line1.removeAllAnimations()
    line2.removeAllAnimations()

    let opacityLine = CABasicAnimation(keyPath: "opacity")
    opacityLine.fromValue = 1.0
    opacityLine.toValue = 0.0
    opacityLine.duration = 0.15

    line1.add(opacityLine, forKey: "disappearLine1")
    line2.add(opacityLine, forKey: "disappearLine2")

    DispatchQueue.main.asyncAfter(deadline: .now() + 0.3, execute: {
        mill.line1.removeFromSuperlayer()
        mill.line2.removeFromSuperlayer()
    })
}

func redrawLines() {

    line1.opacity = 1.0
    line2.opacity = 1.0

    print("redraw")
    line1.removeAllAnimations()
    line2.removeAllAnimations()

    self.layer.addSublayer(line1)
    self.layer.addSublayer(line2)

    let opacityLine = CABasicAnimation(keyPath: "opacity")
    opacityLine.fromValue = 0.0
    opacityLine.toValue = 1.0
    opacityLine.duration = 0.15

    line1.add(opacityMill, forKey: "appearLine1")
    line2.add(opacityMill, forKey: "appearLine2")
}

問題在於，當redrawLines動畫仍在運行時調用undrawLines ，這些行顯示出奇怪的行為，並且不透明度為0。
這是一個演示，第一部分顯示了應該如何，第二部分顯示了錯誤：

Answer 1

我相信這里的問題是您與完成處理程序之間的競爭狀況：

DispatchQueue.main.asyncAfter(deadline: .now() + 0.3, execute: {
    mill.line1.removeFromSuperlayer()
    mill.line2.removeFromSuperlayer()
})

如果您的用戶釋放了，因此在0.3秒的超時之前調用了redrawLines ，則仍然會調用它並刪除行。

您可能想要保留一個指示當前意圖的狀態標志，然后在異步回調中對其進行檢查：

func undrawLines() {

    self.linesHidden = true // update state

    line1.opacity = 0.0
    line2.opacity = 0.0

    line1.removeAllAnimations()
    line2.removeAllAnimations()

    let opacityLine = CABasicAnimation(keyPath: "opacity")
    opacityLine.fromValue = 1.0
    opacityLine.toValue = 0.0
    opacityLine.duration = 0.15

    line1.add(opacityLine, forKey: "disappearLine1")
    line2.add(opacityLine, forKey: "disappearLine2")

    DispatchQueue.main.asyncAfter(deadline: .now() + 0.3, execute: { [weak self] in
        if self?.linesHidden == true { // check this is still what we want to do
            mill.line1.removeFromSuperlayer()
            mill.line2.removeFromSuperlayer()
        }
    })
}

func redrawLines() {

    self.linesHidden = false // update state

    line1.opacity = 1.0
    line2.opacity = 1.0

    print("redraw")
    line1.removeAllAnimations()
    line2.removeAllAnimations()

    self.layer.addSublayer(line1)
    self.layer.addSublayer(line2)

    let opacityLine = CABasicAnimation(keyPath: "opacity")
    opacityLine.fromValue = 0.0
    opacityLine.toValue = 1.0
    opacityLine.duration = 0.15

    line1.add(opacityMill, forKey: "appearLine1")
    line2.add(opacityMill, forKey: "appearLine2")
}

您顯然需要將實例var linesHidden實例添加到該類中，以使其同樣起作用:)