没啥好说的，直接上代码：

public class NumberInputBehaviour : Behavior
     
          {        protected override void OnAttached()        {            base.OnAttached();            InputMethod.SetIsInputMethodEnabled(AssociatedObject, false);            AssociatedObject.PreviewTextInput += AssociatedObject_PreviewTextInput;            AssociatedObject.TextChanged += AssociatedObject_TextChanged;            AssociatedObject.LostFocus += AssociatedObject_LostFocus;        }        protected override void OnDetaching()        {            base.OnDetaching();            AssociatedObject.PreviewTextInput -= AssociatedObject_PreviewTextInput;            AssociatedObject.TextChanged -= AssociatedObject_TextChanged;            AssociatedObject.LostFocus -= AssociatedObject_LostFocus;        }        private void AssociatedObject_LostFocus(object sender, RoutedEventArgs e)        {            if (string.IsNullOrEmpty(AssociatedObject.Text))            {                if (!string.IsNullOrEmpty(NullText))                {                    AssociatedObject.Text = NullText;                }            }        }        private void AssociatedObject_TextChanged(object sender, TextChangedEventArgs e)        {            if (Convert.ToInt32(AssociatedObject.Text) == 0)            {                AssociatedObject.Text = "500";                AssociatedObject.SelectionStart = AssociatedObject.Text.Length;            }        }        private void AssociatedObject_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)        {            Regex re = new Regex("[^0-9]+");            e.Handled = re.IsMatch(e.Text);                 }        public String NullText        {            get { return (String)GetValue(NullTextProperty); }            set { SetValue(NullTextProperty, value); }        }        // Using a DependencyProperty as the backing store for NullText.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty NullTextProperty =            DependencyProperty.Register("NullText", typeof(String), typeof(NumberInputBehaviour), new PropertyMetadata(""));    }
     

xaml 使用方法 ：

OK....