silverlight水印

1.自定义类

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace EasySL.UI.Controls
{

    public class MaskTextBox : TextBox
    {

        #region MaskText

        /// <summary>
        /// view sort style, desc arrow
        /// </summary>
        public static readonly DependencyProperty MaskTextProperty = DependencyProperty.Register("MaskText",typeof(string), typeof(MaskTextBox), new PropertyMetadata(new PropertyChangedCallback(DisplayDataPropertyCallBack)));
        public static void DisplayDataPropertyCallBack(object sender, DependencyPropertyChangedEventArgs args)
        {
        }
        public string MaskText
        {
            get { return (string)GetValue(MaskTextProperty); }
            set { SetValue(MaskTextProperty, value); }
        }

        #endregion
        
        public MaskTextBox()
        {

            Loaded += (sender, args) =>
            {
                if (string.IsNullOrEmpty(base.Text))
                {
                    base.Text = MaskText;
                    base.Foreground = new SolidColorBrush(Colors.Gray);
                }

            };

            base.GotFocus += (sender, args) =>
            {

                base.Foreground = new SolidColorBrush(Colors.Black); 
                if (base.Text == MaskText)
                    base.Text = string.Empty;

            };

            base.LostFocus += (sender, args) =>
            {

                if (!string.IsNullOrEmpty(base.Text))
                    return;
                base.Text = MaskText;
                base.Foreground = new SolidColorBrush(Colors.Gray);

            };

        }
        public new string Text
        {
            get
            {
                if (base.Text == MaskText)
                    return string.Empty;
                else
                    return base.Text;
            }
            set { base.Text = value; }
       }
    }
}

2.在xaml里添加引用

 <local:MaskTextBox Name="userName" MaskText="用户名"  Width="150" Height="30" FontSize="13"/>