带Swift3的CALayer +隐式动画子类 [英] Subclassing CALayer + Implicit Animation w/ Swift3

问题描述

我试图通过重写CALayer来实现隐式动画。我通读了文档，发现它相当复杂。而且，我找不到任何不错的代码示例，也找不到很好的解释或使用任何Swift的互联网帖子。

I am trying to implement "implicit animations" by overriding CALayer. I've read through the documentation and find it rather complicated. More over, I can't find any decent code examples, or internet posts explaining it well or using any Swift.

我由子类 BandBaseCG 实现，该子类试图为属性 param1提供隐式动画，并覆盖了 needsDisplay（forKey：），它的确会用我的属性调用一次，并返回true。

I've implemented by subclass BandBaseCG which attempts to provide implicit animation for property param1, and overridden needsDisplay(forKey:) which does get called once with my property where I return true.

但是这里出了问题。我的理解是，我必须返回一个符合 CAAction 协议的对象，比如说 CABasicAnimation ，这就是我的目的做。但是， action（forKey：）或 defaultAction（forKey：）不会与 param1 键。

But here is where it goes wrong. My understanding is that I must return an object conforming to the CAAction protocol, say a CABasicAnimation, and this is what I do. However, action(forKey:) or defaultAction(forKey:) do not get called with the param1 key.

因此，我了解到可以在 draw（ctx：）中提供Core-Graphics绘图代码响应某些 layer.param1 = 2 来实现实际的隐式动画。但是我到此为止，因为API根本无法按我预期的那样工作。

So I understand that at some point I can provide Core-Graphics drawing code in draw(in ctx:) to implement the actual implicit animation in response to some layer.param1 = 2. But I just cannot get to this point because the API is simply not working how I expected.

这是我当前的实现方式：

Here is my current implementation:

import Foundation
import QuartzCore

class BandBaseCG: CALayer {

   @NSManaged var param1: Float

   override init(layer: Any) {

      super.init(layer: layer)

   }

   override init() {
      super.init()

   }

   required init?(coder aDecoder: NSCoder) {
      fatalError("init(coder:) has not been implemented")
   }


   override func action(forKey event: String) -> CAAction? {

      print(event)

      if event == "param1" {

         let ba = CABasicAnimation(keyPath: event)
         ba.duration = 2
         ba.fromValue = (presentation()! as BandBaseCG).param1
         ba.toValue = 2

         return ba
      }

      return super.action(forKey: event)
   }


   override func draw(in ctx: CGContext) {
      print("draw")
   }


   override class func defaultAction(forKey event: String) -> CAAction?     {

      if event == "param1" {

         let ba = CABasicAnimation(keyPath: event)
         ba.duration = 2
         ba.fromValue = 0
         ba.toValue = 2

         return ba
      }

      return super.defaultAction(forKey: event)
   }

   override class func needsDisplay(forKey key: String) -> Bool {

      print(key)

      if key == "param1" {
         return true
      }

      return super.needsDisplay(forKey: key)
   }

   override func display() {
      print("param value: \(param1)")
   }

}

推荐答案

工作示例（来自我的书）：

Here's a complete working example (from my book):

class MyView : UIView { // exists purely to host MyLayer
    override class var layerClass : AnyClass {
        return MyLayer.self
    }
    override func draw(_ rect: CGRect) {} // so that layer will draw itself
}
class MyLayer : CALayer {
    @NSManaged var thickness : CGFloat
    override class func needsDisplay(forKey key: String) -> Bool {
        if key == #keyPath(thickness) {
            return true
        }
        return super.needsDisplay(forKey:key)
    }
    override func draw(in con: CGContext) {
        let r = self.bounds.insetBy(dx:20, dy:20)
        con.setFillColor(UIColor.red.cgColor)
        con.fill(r)
        con.setLineWidth(self.thickness)
        con.stroke(r)
    }
    override func action(forKey key: String) -> CAAction? {
        if key == #keyPath(thickness) {
            let ba = CABasicAnimation(keyPath: key)
            ba.fromValue = self.presentation()!.value(forKey:key)
            return ba
        }
        return super.action(forKey:key)
    }
}

您会发现，如果将MyView放入应用程序中，则可以说

You will find that if you put a MyView into your app, you can say

let lay = v.layer as! MyLayer
lay.thickness = 10 // or whatever

它将使更改生效在边框的厚度。

and that it will animate the change in the border thickness.

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