CommandBinding question. How to enable command button

Question

My code is here>>

public class Player:INotifyPropertyChanging
{
        string addressBar;
        public string Url
        {
            get {

                return addressBar;
            }
            set { addressBar = value; OnPropertyChanged("Url"); }
        }
        public Regex regVillage = new Regex(@"\?doc=\d+&sys=[a-zA-Z0-9]{2}");

        RelayCommand _AddAttackTask;
        public ICommand AddAttackTask
        {
            get {
                if (_AddAttackTask == null)
                {
                    _AddAttackTask = new RelayCommand(param =>
                    {

                    }, param => this.CanAttack);
                }
                return _AddAttackTask;
            }
        }

        public Boolean CanAttack
        {
            get{
                if (Url == null) return false;
                return regVillage.IsMatch(Url);
            }            
        }
}

On the xaml, i have textbox and button. Textbox binded by url, button binded by AddAttackTask. When i change textbox value,Url changed.Main target is When changing url, button bring to enable or disable. But button always disabled.

I'm getting RelayCommand class from WPF Apps With The Model-View-ViewModel Design Pattern

What is wrong on my code?

Please fix my command binding!

Answer 1

I found it yourself.

Must call CommandManager.InvalidateRequerySuggested(); function after changing property

public string Url
        {
            get {

                return addressBar;
            }
            set { addressBar = value; OnPropertyChanged("Url"); 
                  CommandManager.InvalidateRequerySuggested();
            }
        }