windows phone 水印TextBox

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：

/* ==============================================================================

 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;

            }

        }

    }

}