import UIKit
class LYWTextField: UITextField {
    let LYWPlaceholderLabelKey = "_placeholderLabel.textColor"
    override func awakeFromNib() {
        super.awakeFromNib()
        var count:UInt32 = 0
        let vars = class_copyIvarList(UITextField.self, &count)
        for i in 0..<count {
            let ivar = vars![Int(i)]
            print("\(String(describing: ivar_getName(ivar)))")
        }
        tintColor = textColor
        _ = resignFirstResponder()
    }
    override func becomeFirstResponder() -> Bool {
        self.setValue(textColor, forKeyPath: LYWPlaceholderLabelKey)
        return super.becomeFirstResponder()
    }
    override func resignFirstResponder() -> Bool {
        self.setValue(UIColor.gray, forKeyPath: LYWPlaceholderLabelKey)
        return super.resignFirstResponder()
    }
}