Swift UISearchBar私有属性获取

 /// 寻找子视图
    func findSubview(type: UIResponder.Type, resursion: Bool)-> UIView? {
        for e in self.subviews.enumerated() {
            if e.element.isKind(of: type) {
                return e.element;
            }
        }
        
        if resursion == true {
            for e in self.subviews.enumerated() {
                let tmpView = e.element.findSubview(type: type, resursion: resursion)
                if tmpView != nil {
                    return tmpView;
                }
            }
        }
        return nil;
    }
   
// 使用示例
@objc public extension UISearchBar{
    
    var textfield: UITextField? {
        get {
            var obj = objc_getAssociatedObject(self, RuntimeKeyFromSelector(#function)) as? UITextField;
            if obj == nil {
                obj = self.findSubview(type: UITextField.self, resursion: true) as? UITextField
                objc_setAssociatedObject(self, RuntimeKeyFromSelector(#function), obj, .OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            }
            return obj;
        }
    }
    
    var cancellBtn: UIButton? {
        get {
            var obj = objc_getAssociatedObject(self, RuntimeKeyFromSelector(#function)) as? UIButton;
            if obj == nil {
                obj = self.findSubview(type: (NSClassFromString("UINavigationButton") as! UIResponder.Type).self, resursion: true) as? UIButton
                objc_setAssociatedObject(self, RuntimeKeyFromSelector(#function), obj, .OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            }
            return obj;
        }
    } 
}