如何在 Swift 中检测 UIImageView 上的 UIImageView 更改或 KVO 炒锅

Question

我正在尝试检测 UIImageView (UIimage) 是否已更改或未使用 KeyValueObserver 或任何其他可能的方法，我的图像视图在第一次加载时有一个图像，所以它不是 image.image != nil 我正在使用 UIPickerController，所以当我选择图像时，值会发生变化，我想检测这种变化，以便我可以运行一些代码，例如 Ex：更改按钮的颜色或启用它

btn.backgroundColor = UIColor.green
btn.isEnabled = true

所以我尝试以这种方式添加观察者，但什么也没发生，没有打印输出，没有断点

let driverPImg: UIImageView = {
        let image = UIImageView(image: #imageLiteral(resourceName: "DriverPimg"))
        image.layer.cornerRadius = 75
        image.clipsToBounds = true
        image.contentMode = .scaleAspectFill
        image.isUserInteractionEnabled = true
        image.translatesAutoresizingMaskIntoConstraints = false
        return image
    }()
let key1: String = "key1"
        // in ViewDidLoad
        override func viewDidLoad() {
                super.viewDidLoad()
    
          self.ProfileImg.image!.addObserver(self, forKeyPath: key1, options: .new, context: nil)
    }


override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == key1{
            print("not changed")
        }else{
        print("it did changed")
        }
    }

Answer 1

1. UIImageView 子类
2. 覆盖image属性
3. 在didSet方法中做一些判断

class SUIImageView: UIImageView {
    open var didSetImageBlock: ((_ image: UIImage?) -> Void)?
    open override var image: UIImage? {
        didSet {
            print("did Set image")
            if let didSetImage = didSetImageBlock {
                didSetImage(image)
            }
        }
    }
}

let driverPImg: SUIImageView = {
    let image =  let image = SUIImageView(image: #imageLiteral(resourceName: "DriverPimg"))
    image.layer.cornerRadius = 75
    image.clipsToBounds = true
    image.contentMode = .scaleAspectFill
    image.isUserInteractionEnabled = true
    image.translatesAutoresizingMaskIntoConstraints = false
    return image
}()

// Set the placeholder image before `didSetImageBlock` . So the first time
// you set the placeholder image, `didSetImageBlock` won't be triggered. 
// After the `didSetImageBlock` is set, if the image of the ImageView is 
// changed, `didSetImageBlock` will be triggered. 
driverPImg.didSetImageBlock = { (image: UIImage?) in
    //
    print("did Set Image Block")
}

如果你还想使用 KVO，最好先阅读这个doc。

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