Вы можете создать водяной знак, который можно добавить к любому TextBox с помощью свойства Attached. Вот источник прикрепленного свойства:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Documents;
/// <summary>
/// Class that provides the Watermark attached property
/// </summary>
public static class WatermarkService
{
/// <summary>
/// Watermark Attached Dependency Property
/// </summary>
public static readonly DependencyProperty WatermarkProperty = DependencyProperty.RegisterAttached(
"Watermark",
typeof(object),
typeof(WatermarkService),
new FrameworkPropertyMetadata((object)null, new PropertyChangedCallback(OnWatermarkChanged)));
#region Private Fields
/// <summary>
/// Dictionary of ItemsControls
/// </summary>
private static readonly Dictionary<object, ItemsControl> itemsControls = new Dictionary<object, ItemsControl>();
#endregion
/// <summary>
/// Gets the Watermark property. This dependency property indicates the watermark for the control.
/// </summary>
/// <param name="d"><see cref="DependencyObject"/> to get the property from</param>
/// <returns>The value of the Watermark property</returns>
public static object GetWatermark(DependencyObject d)
{
return (object)d.GetValue(WatermarkProperty);
}
/// <summary>
/// Sets the Watermark property. This dependency property indicates the watermark for the control.
/// </summary>
/// <param name="d"><see cref="DependencyObject"/> to set the property on</param>
/// <param name="value">value of the property</param>
public static void SetWatermark(DependencyObject d, object value)
{
d.SetValue(WatermarkProperty, value);
}
/// <summary>
/// Handles changes to the Watermark property.
/// </summary>
/// <param name="d"><see cref="DependencyObject"/> that fired the event</param>
/// <param name="e">A <see cref="DependencyPropertyChangedEventArgs"/> that contains the event data.</param>
private static void OnWatermarkChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
Control control = (Control)d;
control.Loaded += Control_Loaded;
if (d is ComboBox)
{
control.GotKeyboardFocus += Control_GotKeyboardFocus;
control.LostKeyboardFocus += Control_Loaded;
}
else if (d is TextBox)
{
control.GotKeyboardFocus += Control_GotKeyboardFocus;
control.LostKeyboardFocus += Control_Loaded;
((TextBox)control).TextChanged += Control_GotKeyboardFocus;
}
if (d is ItemsControl && !(d is ComboBox))
{
ItemsControl i = (ItemsControl)d;
// for Items property
i.ItemContainerGenerator.ItemsChanged += ItemsChanged;
itemsControls.Add(i.ItemContainerGenerator, i);
// for ItemsSource property
DependencyPropertyDescriptor prop = DependencyPropertyDescriptor.FromProperty(ItemsControl.ItemsSourceProperty, i.GetType());
prop.AddValueChanged(i, ItemsSourceChanged);
}
}
#region Event Handlers
/// <summary>
/// Handle the GotFocus event on the control
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">A <see cref="RoutedEventArgs"/> that contains the event data.</param>
private static void Control_GotKeyboardFocus(object sender, RoutedEventArgs e)
{
Control c = (Control)sender;
if (ShouldShowWatermark(c))
{
ShowWatermark(c);
}
else
{
RemoveWatermark(c);
}
}
/// <summary>
/// Handle the Loaded and LostFocus event on the control
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">A <see cref="RoutedEventArgs"/> that contains the event data.</param>
private static void Control_Loaded(object sender, RoutedEventArgs e)
{
Control control = (Control)sender;
if (ShouldShowWatermark(control))
{
ShowWatermark(control);
}
}
/// <summary>
/// Event handler for the items source changed event
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">A <see cref="EventArgs"/> that contains the event data.</param>
private static void ItemsSourceChanged(object sender, EventArgs e)
{
ItemsControl c = (ItemsControl)sender;
if (c.ItemsSource != null)
{
if (ShouldShowWatermark(c))
{
ShowWatermark(c);
}
else
{
RemoveWatermark(c);
}
}
else
{
ShowWatermark(c);
}
}
/// <summary>
/// Event handler for the items changed event
/// </summary>
/// <param name="sender">The source of the event.</param>
/// <param name="e">A <see cref="ItemsChangedEventArgs"/> that contains the event data.</param>
private static void ItemsChanged(object sender, ItemsChangedEventArgs e)
{
ItemsControl control;
if (itemsControls.TryGetValue(sender, out control))
{
if (ShouldShowWatermark(control))
{
ShowWatermark(control);
}
else
{
RemoveWatermark(control);
}
}
}
#endregion
#region Helper Methods
/// <summary>
/// Remove the watermark from the specified element
/// </summary>
/// <param name="control">Element to remove the watermark from</param>
private static void RemoveWatermark(UIElement control)
{
AdornerLayer layer = AdornerLayer.GetAdornerLayer(control);
// layer could be null if control is no longer in the visual tree
if (layer != null)
{
Adorner[] adorners = layer.GetAdorners(control);
if (adorners == null)
{
return;
}
foreach (Adorner adorner in adorners)
{
if (adorner is WatermarkAdorner)
{
adorner.Visibility = Visibility.Hidden;
layer.Remove(adorner);
}
}
}
}
/// <summary>
/// Show the watermark on the specified control
/// </summary>
/// <param name="control">Control to show the watermark on</param>
private static void ShowWatermark(Control control)
{
AdornerLayer layer = AdornerLayer.GetAdornerLayer(control);
// layer could be null if control is no longer in the visual tree
if (layer != null)
{
layer.Add(new WatermarkAdorner(control, GetWatermark(control)));
}
}
/// <summary>
/// Indicates whether or not the watermark should be shown on the specified control
/// </summary>
/// <param name="c"><see cref="Control"/> to test</param>
/// <returns>true if the watermark should be shown; false otherwise</returns>
private static bool ShouldShowWatermark(Control c)
{
if (c is ComboBox)
{
return (c as ComboBox).Text == string.Empty;
}
else if (c is TextBoxBase)
{
return (c as TextBox).Text == string.Empty;
}
else if (c is ItemsControl)
{
return (c as ItemsControl).Items.Count == 0;
}
else
{
return false;
}
}
#endregion
}
Присоединенное свойство использует класс с именем WatermarkAdorner, вот этот источник:
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Media;
/// <summary>
/// Adorner for the watermark
/// </summary>
internal class WatermarkAdorner : Adorner
{
#region Private Fields
/// <summary>
/// <see cref="ContentPresenter"/> that holds the watermark
/// </summary>
private readonly ContentPresenter contentPresenter;
#endregion
#region Constructor
/// <summary>
/// Initializes a new instance of the <see cref="WatermarkAdorner"/> class
/// </summary>
/// <param name="adornedElement"><see cref="UIElement"/> to be adorned</param>
/// <param name="watermark">The watermark</param>
public WatermarkAdorner(UIElement adornedElement, object watermark) :
base(adornedElement)
{
this.IsHitTestVisible = false;
this.contentPresenter = new ContentPresenter();
this.contentPresenter.Content = watermark;
this.contentPresenter.Opacity = 0.5;
this.contentPresenter.Margin = new Thickness(Control.Margin.Left + Control.Padding.Left, Control.Margin.Top + Control.Padding.Top, 0, 0);
if (this.Control is ItemsControl && !(this.Control is ComboBox))
{
this.contentPresenter.VerticalAlignment = VerticalAlignment.Center;
this.contentPresenter.HorizontalAlignment = HorizontalAlignment.Center;
}
// Hide the control adorner when the adorned element is hidden
Binding binding = new Binding("IsVisible");
binding.Source = adornedElement;
binding.Converter = new BooleanToVisibilityConverter();
this.SetBinding(VisibilityProperty, binding);
}
#endregion
#region Protected Properties
/// <summary>
/// Gets the number of children for the <see cref="ContainerVisual"/>.
/// </summary>
protected override int VisualChildrenCount
{
get { return 1; }
}
#endregion
#region Private Properties
/// <summary>
/// Gets the control that is being adorned
/// </summary>
private Control Control
{
get { return (Control)this.AdornedElement; }
}
#endregion
#region Protected Overrides
/// <summary>
/// Returns a specified child <see cref="Visual"/> for the parent <see cref="ContainerVisual"/>.
/// </summary>
/// <param name="index">A 32-bit signed integer that represents the index value of the child <see cref="Visual"/>. The value of index must be between 0 and <see cref="VisualChildrenCount"/> - 1.</param>
/// <returns>The child <see cref="Visual"/>.</returns>
protected override Visual GetVisualChild(int index)
{
return this.contentPresenter;
}
/// <summary>
/// Implements any custom measuring behavior for the adorner.
/// </summary>
/// <param name="constraint">A size to constrain the adorner to.</param>
/// <returns>A <see cref="Size"/> object representing the amount of layout space needed by the adorner.</returns>
protected override Size MeasureOverride(Size constraint)
{
// Here's the secret to getting the adorner to cover the whole control
this.contentPresenter.Measure(Control.RenderSize);
return Control.RenderSize;
}
/// <summary>
/// When overridden in a derived class, positions child elements and determines a size for a <see cref="FrameworkElement"/> derived class.
/// </summary>
/// <param name="finalSize">The final area within the parent that this element should use to arrange itself and its children.</param>
/// <returns>The actual size used.</returns>
protected override Size ArrangeOverride(Size finalSize)
{
this.contentPresenter.Arrange(new Rect(finalSize));
return finalSize;
}
#endregion
}
Теперь вы можете поставить водяной знак на любом текстовом поле, например так:
<AdornerDecorator>
<TextBox x:Name="SearchTextBox">
<controls:WatermarkService.Watermark>
<TextBlock>Type here to search text</TextBlock>
</controls:WatermarkService.Watermark>
</TextBox>
</AdornerDecorator>
Водяной знак может быть любым, что вы хотите (текст, изображения ...). В дополнение к работе с TextBoxes, этот водяной знак также работает для ComboBoxes и ItemControls.
Этот код был адаптирован из этого сообщения в блоге .