iOS：检测我的 UIView 何时添加到其他视图中

在iOS开发中，我们经常需要检测一个UIView何时被添加到其他视图中。这对于我们在视图层次结构中执行特定操作或进行一些UI调整非常有用。幸运的是，在iOS中，我们可以通过使用KVO（键值观察）来轻松地实现这一点。

swift
import UIKit
class CustomView: UIView {
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        // Add KVO observer for superview property
        self.addObserver(self, forKeyPath: "superview", options: .new, context: nil)
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        
        // Add KVO observer for superview property
        self.addObserver(self, forKeyPath: "superview", options: .new, context: nil)
    }
    
    deinit {
        // Remove KVO observer when the view is deallocated
        self.removeObserver(self, forKeyPath: "superview")
    }
    
    // KVO observation callback
    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        if keyPath == "superview" {
            if self.superview != nil {
                // View is added to another view
                print("View is added to another view")
            } else {
                // View is removed from its superview
                print("View is removed from its superview")
            }
        }
    }
}

swift
// Create a superview
let superview = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
// Create a custom view
let customView = CustomView(frame: CGRect(x: 50, y: 50, width: 100, height: 100))
// Add custom view to superview
superview.addSubview(customView)
// Output: View is added to another view
// Remove custom view from superview
customView.removeFromSuperview()
// Output: View is removed from its superview