原理：在失去焦点和获取焦点的时候，判断Text值是否为空或者是否与水印值相同，然后修改TextBox中的Text和Foreground。
代码如下：
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/* ============================================================================== 2 * 类名称：WatermarkTextBox 3 * 类描述： 4 * 创建人：neoyee 5 * 创建时间：2014/2/25 17:24:11 6 * 修改人： 7 * 修改时间： 8 * 修改备注： 9 * @version 1.010 * ==============================================================================*/using
System;using
System.Collections.Generic;using
System.Linq;using
System.Text;using
System.Threading.Tasks;using
System.Windows;using
System.Windows.Controls;using
System.Windows.Media;using
Windows.UI;namespace
WP8.Controls{ public
sealed class WatermarkTextBox : TextBox { private
static readonly DependencyProperty WatermarkTextProperty = DependencyProperty.Register("WatermarkText", typeof(string), typeof(WatermarkTextBox), new
PropertyMetadata(string.Empty, new
PropertyChangedCallback(WatermarkTextChanged))); private
static readonly DependencyProperty WatermarkForegroundProperty = DependencyProperty.Register("WatermarkForeground", typeof(SolidColorBrush), typeof(WatermarkTextBox), new
PropertyMetadata(new
SolidColorBrush(Colors.Black))); private
static readonly DependencyProperty WatermarkBackgroundProperty = DependencyProperty.Register("WatermarkBackground", typeof(SolidColorBrush), typeof(WatermarkTextBox), new
PropertyMetadata(new
SolidColorBrush(Colors.White))); private
static readonly DependencyProperty NormalForegroundProperty = DependencyProperty.Register("NormalForeground", typeof(SolidColorBrush), typeof(WatermarkTextBox), new
PropertyMetadata(new
SolidColorBrush(Colors.Black), NormalForegroundPropertyChanged)); private
static readonly DependencyProperty NormalBackgroundProperty = DependencyProperty.Register("NormalBackground", typeof(SolidColorBrush), typeof(WatermarkTextBox), new
PropertyMetadata(new
SolidColorBrush(Colors.White))); private
static void NormalForegroundPropertyChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args) { var
watermarkTextBox = obj as
WatermarkTextBox; if
(watermarkTextBox != null) watermarkTextBox.NormalForegroundChanged((SolidColorBrush)args.NewValue); } private
void NormalForegroundChanged(SolidColorBrush value) { Foreground = value; } public
SolidColorBrush NormalBackground { get
{ return
(SolidColorBrush)GetValue(NormalBackgroundProperty); } set
{ SetValue(NormalBackgroundProperty, value); } } public
SolidColorBrush NormalForeground { get
{ return
(SolidColorBrush)GetValue(NormalForegroundProperty); } set
{ SetValue(NormalForegroundProperty, value); } } public
SolidColorBrush WatermarkBackground { get
{ return
(SolidColorBrush)GetValue(WatermarkBackgroundProperty); } set
{ SetValue(WatermarkBackgroundProperty, value); } } public
SolidColorBrush WatermarkForeground { get
{ return
(SolidColorBrush)GetValue(WatermarkForegroundProperty); } set
{ SetValue(WatermarkForegroundProperty, value); } } public
string WatermarkText { get
{ return
(string)GetValue(WatermarkTextProperty); } set
{ SetValue(WatermarkTextProperty, value); } } public
WatermarkTextBox() { this.LostFocus += WatermarkTextBox_LostFocus; this.GotFocus += WatermarkTextBox_GotFocus; this.TextChanged += WatermarkTextBox_TextChanged; if
(string.IsNullOrEmpty(this.Text)) { this.Text = WatermarkText; Foreground = WatermarkForeground; } } void
WatermarkTextBox_TextChanged(object
sender, TextChangedEventArgs e) { if
(Text == WatermarkText) { this.Text = WatermarkText; Foreground = WatermarkForeground; } else
if (Text != WatermarkText) { Foreground = NormalForeground; } } private
static void WatermarkTextChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args) { ((WatermarkTextBox)obj).WatermarkTextChanged(args.OldValue, args.NewValue); } private
void WatermarkTextChanged(object
OldValue, object
NewValue) { } void
WatermarkTextBox_GotFocus(object
sender, RoutedEventArgs e) { if
(this.Text == WatermarkText && Foreground == WatermarkForeground) { this.Text = string.Empty; Foreground = NormalForeground; } } void
WatermarkTextBox_LostFocus(object
sender, RoutedEventArgs e) { if
(string.IsNullOrEmpty(this.Text) || Text == WatermarkText) { this.Text = WatermarkText; Foreground = WatermarkForeground; } } }} |
原文：http://www.cnblogs.com/betterchaner/p/3567365.html