Using WPF Validation rules and the disabling of a 'Save' button

Question

I have a page where a few textboxes cannot be empty before clicking a Save button.

Answer 1

Here is a helper method which tracks validation errors on the dependency objects (and all its children) and calls delegate to notify about the change. It also tracks removal of the children with validation errors.

 public static void AddErrorHandler(DependencyObject element, Action setHasValidationErrors)
        {
            var errors = new List>();

            RoutedEventHandler sourceUnloaded = null;

            sourceUnloaded = (sender, args) =>
                {
                    if (sender is FrameworkElement)
                        ((FrameworkElement) sender).Unloaded -= sourceUnloaded;
                    else
                        ((FrameworkContentElement) sender).Unloaded -= sourceUnloaded;

                    foreach (var error in errors.Where(err => err.Item1 == sender).ToArray())
                        errors.Remove(error);

                    setHasValidationErrors(errors.Any());
                };

            EventHandler errorHandler = (_, args) =>
                {
                    if (args.Action == ValidationErrorEventAction.Added)
                    {
                        errors.Add(new Tuple(args.OriginalSource, args.Error));

                        if (args.OriginalSource is FrameworkElement)
                            ((FrameworkElement)args.OriginalSource).Unloaded += sourceUnloaded;
                        else if (args.OriginalSource is FrameworkContentElement)
                            ((FrameworkContentElement)args.OriginalSource).Unloaded += sourceUnloaded;
                    }
                    else
                    {
                        var error = errors
                            .FirstOrDefault(err => err.Item1 == args.OriginalSource && err.Item2 == args.Error);

                        if (error != null) 
                            errors.Remove(error);
                    }

                    setHasValidationErrors(errors.Any());
                };


            System.Windows.Controls.Validation.AddErrorHandler(element, errorHandler);
        }