Swift 中系统 API delegate 参数一定要在当前类实现传 self 吗

因为要写原生插件，swift 刚接触，语法比 objc 好看多了。

在开发相机组件时遇到一个问题，AVCapturePhotoCaptureDelegate 契约用自定义 UIView/UIViewController 实现没问题， 换成独立的类实现就回调不了，不是什么原因。

上代码：

TakePhotoDelegate.swift

import Foundation import AVFoundation import UIKit public typealias TakePhotoCallback = ((String, String) -> Void)?; class TakePhotoWithCompletion : NSObject, AVCapturePhotoCaptureDelegate { // ... var completion: TakePhotoCallback; init(callback: TakePhotoCallback) { self.completion = callback; super.init(); } func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) { // todo sth self.completion!("{file path}", "{error}"); } } 

CameraxView.swift

import AVFoundation import UIKit class CameraxView: UIView { // ... @objc func takePhoto(options: Dictionary<String, String>, completion: TakePhotoCallback) { let photoSettings = AVCapturePhotoSettings.init(format:[AVVideoCodecKey:AVVideoCodecType.jpeg]) let delegate = TakePhotoWithCompletion.init(callback: completion) imageOutPut?.capturePhoto(with:photoSettings, delegate: delegate) } // ... } 

点击拍照按钮能听到快门声，但是 photoOutput 没有回调

如果换成如下自定义 UIView 实现 AVCapturePhotoCaptureDelegate 没有问题，能正常回调

import AVFoundation import UIKit class CameraxView: UIView, AVCapturePhotoCaptureDelegate { // ... var completion: TakePhotoCallback = nil; @objc func takePhoto(options: Dictionary<String, String>) { let photoSettings = AVCapturePhotoSettings.init(format:[AVVideoCodecKey:AVVideoCodecType.jpeg]) self.completion = completion imageOutPut?.capturePhoto(with:photoSettings, delegate: self) } @objc func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) { // todo sth self.completion!("{file path}", "{error}"); } // ... } 

有这个差异的原因是因为系统 API 的限制吗还是 swift 语言层面问题， 如果 takePhoto 方法希望传闭包参数回调拍照结果，正确应该怎么写。

（回调参数赋值给实例对象, 个人感觉是个很奇怪的做法）