WPF

var propertyMetadata = new FrameworkPropertyMetadata(1.0, OnIncrementChanged, OnCoerceIncrementProperty);
IncrementProperty = DependencyProperty.Register("Increment",
                                                typeof (Double),
                                                typeof (NumericTextBox),
                                                propertyMetadata,
                                                IsIncrementValid);

 public static readonly DependencyProperty IncrementProperty;

 [EditorBrowsable]
 public Double Increment
 {
     get { return (Double) GetValue(IncrementProperty); }
     set { SetValue(IncrementProperty, value); }
 }

 private static object OnCoerceIncrementProperty(DependencyObject sender, object data)
 {
     var value = (Double) data;
     var numericTextBox = (NumericTextBox) sender;

     if (numericTextBox.IsWholeNumberOnly)
     {
         return 1.0;
     }

     if (value > 0 && value <= 1)
     {
         return value;
     }

     return 1.0;
 }

 private static void OnIncrementChanged(DependencyObject obj, DependencyPropertyChangedEventArgs eventArgs){}

 // Note that this a validation for the type, not an instance!
 private static bool IsIncrementValid(object value)
 {
     var val = (Double) value;
     return val > 0 && val <= 1;
 }