<UserControl x:Class="TextBoxEdit.SelfWateMarkTextbox"             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"              mc:Ignorable="d"  >    <Grid>        <StackPanel Orientation="Horizontal" Height="35">            <Label Name="IsInput" Foreground="Red" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" Width="20">*</Label>            <TextBox VerticalContentAlignment="Center"  Width="300" Height="25" x:Name="textBox1"  />            <Border  Name="IsErrorShowBorder" BorderThickness="1"  Height="27" CornerRadius="15"  Visibility="Hidden">                <Label Name="IsError"  Foreground="Red" Background="LightPink" VerticalContentAlignment="Center" HorizontalContentAlignment="Center">错误信息</Label>            </Border>            <TextBox VerticalContentAlignment="Center" Text="{Binding IsErroShow}"  Height="25" x:Name="txtErrorShow"   Visibility="Hidden"/>        </StackPanel>    </Grid></UserControl>

private const string defaultText = "";        private const string IsInputText = "";        private const string IsErrorText = "";        public SelfWateMarkTextbox()        {            InitializeComponent();            this.Loaded += new RoutedEventHandler(WateMarkTextbox_Loaded);            this.GotFocus += new RoutedEventHandler(WateMarkTextbox_GotFocus);            this.LostFocus += new RoutedEventHandler(WateMarkTextbox_LostFocus);            this.textBox1.TextChanged += new TextChangedEventHandler(TextBox1_TextChanged);            this.txtErrorShow.TextChanged += new TextChangedEventHandler(txtErrorShow_TextChanged);        }        void txtErrorShow_TextChanged(object sender, TextChangedEventArgs e)        {            if (!string.IsNullOrWhiteSpace(this.txtErrorShow.Text) && txtErrorShow.Text.ToLower() == "true")            {                IsErrorShowBorder.Visibility = Visibility.Visible;            }            else            {                IsErrorShowBorder.Visibility = Visibility.Hidden;            }        }        void TextBox1_TextChanged(object sender, TextChangedEventArgs e)        {            if (!string.IsNullOrWhiteSpace(this.textBox1.Text) || this.textBox1.IsFocused)            {                this.textBox1.Text = this.textBox1.Text;            }            else            {                this.textBox1.Text = Watermark;            }        }        void WateMarkTextbox_LostFocus(object sender, RoutedEventArgs e)        {            if (string.IsNullOrEmpty(this.textBox1.Text))            {                this.textBox1.Text = string.Empty;            }        }        void WateMarkTextbox_GotFocus(object sender, RoutedEventArgs e)        {            if (this.textBox1.Text.Equals(Watermark))            {                this.textBox1.Text = string.Empty;            }        }        void WateMarkTextbox_Loaded(object sender, RoutedEventArgs e)        {            this.textBox1.Text = Watermark;            this.IsInput.Content = IsRequired;            this.IsError.Content = IsErrorMessage;        }        public string Watermark        {            get            {                string result = (string)GetValue(WatermarkProperty);                if (string.IsNullOrEmpty(result))                {                    result = defaultText;                }                return result;            }            set { SetValue(WatermarkProperty, value); }        }        public string IsRequired        {            get            {                string result = (string)GetValue(IsRequiredProperty);                if (string.IsNullOrEmpty(result))                {                    result = IsInputText;                }                return result;            }            set { SetValue(IsRequiredProperty, value); }        }        public string IsErrorMessage        {            get            {                string result = (string)GetValue(IsErrorMessageProperty);                if (string.IsNullOrEmpty(result))                {                    result = IsErrorText;                }                return result;            }            set { SetValue(IsErrorMessageProperty, value); }        }        public string IsErrorShow        {            set            {                txtErrorShow.Text = null;                txtErrorShow.Text = value;            }        }        readonly DependencyProperty WatermarkProperty =                   DependencyProperty.Register("Watermark", typeof(string), typeof(SelfWateMarkTextbox), new UIPropertyMetadata(defaultText));        public static readonly DependencyProperty IsRequiredProperty =             DependencyProperty.Register("IsRequired", typeof(string), typeof(SelfWateMarkTextbox), new UIPropertyMetadata(IsInputText));        public static readonly DependencyProperty IsErrorMessageProperty =            DependencyProperty.Register("IsErrorMessage", typeof(string), typeof(SelfWateMarkTextbox), new UIPropertyMetadata(IsErrorText));

 <my:SelfWateMarkTextbox  x:Name="wateMarkTextbox1" VerticalAlignment="Top"  IsRequired="*"  Watermark="请输入姓名" IsErrorMessage="请输入正常的姓名"  Height="35" />        <Button Content="确定" Height="23" Width="120" Click="Button_Click"></Button>

private void Button_Click(object sender, RoutedEventArgs e)        {            wateMarkTextbox1.IsErrorShow = "true";        }