无法识别UIImageWriteToSavedPhotosAlbum中的Swift Selector，为什么？

Question

的iOS API函数UIImageWriteToSavedPhotosAlbum需要选择作为一个argment：

func UIImageWriteToSavedPhotosAlbum(_ image: UIImage, 
           _ completionTarget: Any?, 
           _ completionSelector: Selector?, 
           _ contextInfo: UnsafeMutableRawPointer?) 

https://developer.apple.com/documentation/uikit/1619125-uiimagewritetosavedphotosalbum

然而，在迅速，当我调用该函数，选择永远不会被认可：

class Base { 
    func save_image(img:UIImage) { 
     UIImageWriteToSavedPhotosAlbum(img, self, Selector("image:didFinishSavingWithError:contextInfo:"), nil) 
     // I also tried this: 
     // UIImageWriteToSavedPhotosAlbum(img, self, #selector(image(_:didFinishSavingWithError:contextInfo:)) 
    } 

    @objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) { 
     print("Photo Saved Successfully") 
    } 
} 

class Child:Base { 
} 

// This is how I call the save_image function: 
let child = Child() 
child.save_image() 

由于你可以看到，我尝试从签名和字符串构造选择器，但都不起作用。我总是在运行时遇到这个错误：

'XXX.Child' does not implement methodSignatureForSelector: -- trouble ahead 
Unrecognized selector ...... 

这里发生了什么？我想知道这是否是因为swift没有看到Child类的方法，因为该方法是从Base类继承的？

如何成功传递选择器？

相关的问题我已阅读：

@selector() in Swift?

Answer 1

提供一些指导你的选择，以帮助其找到合适的功能：

class Base { 
    func save_image(img:UIImage) { 
     UIImageWriteToSavedPhotosAlbum(img, self, #selector(Base.image(_:didFinishSavingWithError:contextInfo:)), nil) 
    } 

    @objc func image(_ image: UIImage, didFinishSavingWithError error: Error?, contextInfo: UnsafeRawPointer) { 
     print("Photo Saved Successfully") 
    } 
} 

class Child:Base { 
} 

// This is how I call the save_image function: 
let child = Child() 
child.save_image() 

Answer 2

methodSignatureForSelector是NSObject的的方法。 所以，你需要继承NSObject类。

class Base: NSObject { 
    ... 
}