Update UI from ViewModel class (MVVM pattern) in WPF

Question

I\'m using the MVVM pattern in my first WPF app and have a problem with something quite basic I assume.

When the user hits the \"save\" button on my view, a command

Answer 1

You could always do something like this:

public class SaveDemo : INotifyPropertyChanged
{
  public event PropertyChangedEventHandler PropertyChanged;
  private bool _canSave;

  public bool CanSave
  {
    get { return _canSave; }
    set
    {
      if (_canSave != value)
      {
        _canSave = value;
        OnChange("CanSave");
      }
    }
  }

  public void Save()
  {
    _canSave = false;

    // Do the lengthy operation
    _canSave = true;
  }

  private void OnChange(string p)
  {
    PropertyChangedEventHandler handler = PropertyChanged;
    if (handler != null)
    {
      handler(this, new PropertyChangedEventArgs(p));
    }
  }
}

Then you could bind the IsEnabled property of the button to the CanSave property, and it will automatically be enabled/disabled. An alternative method, and one I would go with would be to use the Command CanExecute to sort this, but the idea is similar enough for you to work with.