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）