Swift中的子类不会继承其超类的初始化程序 [英] Subclass in Swift does not inherit initialiser of its superclass

问题描述

在尝试对NSBezierPath进行子类化时，我偶然发现了一个非常奇怪的问题.

I have stumbled upon a very strange issue when trying to subclass NSBezierPath.

下面是我的子类的定义:

Below is the definition of my subclass:

class OSBezierPath: NSBezierPath {
        
    func addLineToPoint(point:CGPoint) {
        self.lineToPoint(point)
    }
}

除了无法访问NSBezierPath的某些初始化程序外，该子类的工作原理也不同.例如，下面的行无效:

This subclass works apart from the fact that I cannot access some of the initialisers of the NSBezierPath. For example, line below is invalid:

let path = OSBezierPath(ovalInRect: rect)

编译器抛出错误

调用中的额外参数'ovalInRect'

Extra argument 'ovalInRect' in call

此错误的原因

另一个问题对此原因进行了很好的解释.但是，建议的答案对我来说效果不佳，因为我要实现的目标是在iOS和Mac OS上都使用OSBezierPath.

Cause of this bug

Cause of this bug is well-explained in another question. However, the suggested answer doesn't work well for me because what I am trying to achieve is to use OSBezierPath on both iOS and Mac OS.

我的原始代码是这样的:

My original code read like this:

#if os(iOS)
    typealias OSBezierPath = UIBezierPath
#else
    class OSBezierPath: NSBezierPath {
        
        func addLineToPoint(point:CGPoint) {
            self.lineToPoint(point)
        }
    }
#endif

此代码不起作用，但是我发现有2个变通方法，比起另一个问题的建议答案，它更适合我的目的.

This code doesn't work, but I have found 2 workarounds which are more elegant for my purpose than the suggested answer in another question.

推荐答案

第一个解决方案

此解决方案使用扩展名将功能添加到NSBezierPath，这将使其能够以与UIBezierPath相同的方式绘制线条.

1st solution

This solution uses extension to add a function to NSBezierPath which will allow it to draw lines in the same way as UIBezierPath.

#if os(iOS)
    typealias OSBezierPath = UIBezierPath
#else
    typealias OSBezierPath = NSBezierPath
    
    extension OSBezierPath {
        func addLineToPoint(point:CGPoint) {
            self.lineToPoint(point)
        }
    }
#endif

这避免了任何潜在的错误，因为不涉及子类.因此，请在下面一行:

This avoids any potential bug because there is no subclassing involved. Therefore, line below:

let path = OSBezierPath(ovalInRect: rect)

实际上翻译为:

let path = NSBezierPath(ovalInRect: rect)

所以编译器很高兴:)

第二个解决方案使用了UIBezierPath的类函数已在Xcode 7中转换为适当的初始化程序这一事实，因此，下面的代码将起作用:

Second solution uses the fact that class functions of UIBezierPath were converted to proper initialisers in Xcode 7. So, code below will work:

#if os(iOS)
    class OSBezierPath: UIBezierPath {
        func lineToPoint(point:CGPoint) {
            self.addLineToPoint(point)
        }
    }
#else
    typealias OSBezierPath = NSBezierPath
#endif

这允许我们通过在iOS和Mac OS上调用lineToPoint来使用OSBezierPath.

This allows us to use OSBezierPath by calling lineToPoint on both iOS and Mac OS.

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