SwiftUI UIViewControllerRepresentable，Coordinator(self) 是什么意思？

Question

在制作 UIViewControllerRepresentable（在 SwiftUI 中使用 UIKit 组件）时，Coordinator(self) 意味着什么？ 我对“自我”代表什么有点困惑。

import SwiftUI

struct ImagePicker: UIViewControllerRepresentable {
    @Binding var image: UIImage?
    @Environment(\.presentationMode) var presentationMode

    class Coordinator: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
        var parent: ImagePicker
        
        init(_ parent: ImagePicker) {
            self.parent = parent
        }
        
        func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
            if let uiImage = info[.originalImage] as? UIImage {
                parent.image = uiImage
            }
            
            parent.presentationMode.wrappedValue.dismiss()
        }
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
    
    func makeUIViewController(context: Context) -> UIImagePickerController {
        let picker = UIImagePickerController()
        picker.delegate = context.coordinator
        return picker
    }
    
    func updateUIViewController(_ uiViewController: UIImagePickerController, context: Context) {
        
    }
}

Answer 1

不幸的是，在许多例子中，

Coordinator(self)

是一个错误。

self

表示 SwiftUI 更新后立即丢弃的结构，因此协调器对象挂在它上面是没有意义的。任何对

self

的函数调用都不会执行任何操作。正确的方法是

Coordinator()

，Apple 的

Fruta 示例

中的 PaymentButton.swift 中有一个示例。通过此更改，您的代码将类似于：

import SwiftUI

struct ImagePicker: UIViewControllerRepresentable {
    @Binding var image: UIImage?
    @Environment(\.presentationMode) var presentationMode


    func makeCoordinator() -> Coordinator {
        Coordinator()
    }

    func makeUIViewController(context: Context) -> UIImagePickerController {
        context.coordinator.imagePicker       
    }
    
    func updateUIViewController(_ uiViewController: UIImagePickerController, context: Context) {
        context.coordinator.didPickImage = { image in
            self.image = image
        }
    }

    class Coordinator: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
        
        lazy var imagePicker: UIImagePickerController =  {
            let picker = UIImagePickerController()
            picker.delegate = self
            return picker
        }()
        
        var didPickImage: ((Void) -> UIImage)?

        func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
            if let uiImage = info[.originalImage] as? UIImage {
                didPickImage?(uiImage)
            }
        }
    }
    

}

Answer 2

self

始终表示“当前实例”。所以当你写...

struct ImagePicker: UIViewControllerRepresentable {
    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }
}

...

self

表示“此 ImagePicker 实例”。

您这样说是因为协调器的初始化程序的声明方式：

class Coordinator: NSObject, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    var parent: ImagePicker
    init(_ parent: ImagePicker) {
        self.parent = parent
    }
}

协调器需要一个

parent

才能初始化；你正在初始化一个协调器，并且你告诉它

parent

应该是谁，即你（即

self

，这个ImagePicker）。

如果这些概念给您带来麻烦，您可能需要研究什么是类型和实例（面向对象编程）和/或 Swift 初始化器和初始化是如何表达的。