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 1.0
10 * ==============================================================================*/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;
}
}
}
} |