NSTextField subclass with focus and blur callback.

TextField.swift

import Cocoa

protocol TextFieldDelegate: class {
    func textFieldDidBecomeFirstResponder(_ textField: TextField)
    func textFieldDidResignFirstResponder(_ textField: TextField)
}

class TextField: NSTextField {

    weak var firstResponderDelegate: TextFieldDelegate?

    private var isFocused = false {
        didSet {
            if isFocused {
                firstResponderDelegate?.textFieldDidBecomeFirstResponder(self)
            } else {
                firstResponderDelegate?.textFieldDidResignFirstResponder(self)
            }
        }
    }

    override func resignFirstResponder() -> Bool {
        let willResign = super.resignFirstResponder()
        
        if willResign, let _ = currentEditor() {
            isFocused = true
        }
        
        return status
    }
    
    override func textDidEndEditing(_ notification: Notification) {
        super.textDidEndEditing(notification)
        if currentEditor() == nil { 
            onceFocus = false
        }
    }
    
}