好吧，这是我的:不一定是最好的，但因为它很简单，很容易编辑到你的口味。

<UserControl x:Class="WPFControls.ShadowedTextBox"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WPFControls"
    Name="Root">
<UserControl.Resources>
    <local:ShadowConverter x:Key="ShadowConvert"/>
</UserControl.Resources>
<Grid>
    <TextBox Name="textBox" 
             Foreground="{Binding ElementName=Root, Path=Foreground}"
             Text="{Binding ElementName=Root, Path=Text, UpdateSourceTrigger=PropertyChanged}"
             TextChanged="textBox_TextChanged"
             TextWrapping="Wrap"
             VerticalContentAlignment="Center"/>
    <TextBlock Name="WaterMarkLabel"
           IsHitTestVisible="False"
           Foreground="{Binding ElementName=Root,Path=Foreground}"
           FontWeight="Thin"
           Opacity=".345"
           FontStyle="Italic"
           Text="{Binding ElementName=Root, Path=Watermark}"
           VerticalAlignment="Center"
           TextWrapping="Wrap"
           TextAlignment="Center">
        <TextBlock.Visibility>
            <MultiBinding Converter="{StaticResource ShadowConvert}">
                <Binding ElementName="textBox" Path="Text"/>
            </MultiBinding>
        </TextBlock.Visibility> 
    </TextBlock>
</Grid>

这个转换器，就像它现在写的那样，它不一定是一个MultiConverter，但这样它可以很容易地扩展

using System;
using System.Globalization;
using System.Windows;
using System.Windows.Data;

namespace WPFControls
{
    class ShadowConverter:IMultiValueConverter
    {
        #region Implementation of IMultiValueConverter

        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            var text = (string) values[0];
            return text == string.Empty
                       ? Visibility.Visible
                       : Visibility.Collapsed;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            return new object[0];
        }

        #endregion
    }
}

最后是背后的代码:

using System.Windows;
using System.Windows.Controls;

namespace WPFControls
{
    /// <summary>
    /// Interaction logic for ShadowedTextBox.xaml
    /// </summary>
    public partial class ShadowedTextBox : UserControl
    {
        public event TextChangedEventHandler TextChanged;

        public ShadowedTextBox()
        {
            InitializeComponent();
        }

        public static readonly DependencyProperty WatermarkProperty =
            DependencyProperty.Register("Watermark",
                                        typeof (string),
                                        typeof (ShadowedTextBox),
                                        new UIPropertyMetadata(string.Empty));

        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register("Text",
                                        typeof (string),
                                        typeof (ShadowedTextBox),
                                        new UIPropertyMetadata(string.Empty));

        public static readonly DependencyProperty TextChangedProperty =
            DependencyProperty.Register("TextChanged",
                                        typeof (TextChangedEventHandler),
                                        typeof (ShadowedTextBox),
                                        new UIPropertyMetadata(null));

        public string Watermark
        {
            get { return (string)GetValue(WatermarkProperty); }
            set
            {
                SetValue(WatermarkProperty, value);
            }
        }

        public string Text
        {
            get { return (string) GetValue(TextProperty); }
            set{SetValue(TextProperty,value);}
        }

        private void textBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            if (TextChanged != null) TextChanged(this, e);
        }

        public void Clear()
        {
            textBox.Clear();
        }

    }
}

看看另一个简单的解决方案:

我专注于“得到专注”和“失去专注”事件。

XAML:

<Grid>
<TextBlock x:Name="DosyaİhtivaEdenDizinYansıması" Text="Hedef Dizin Belirtin" VerticalAlignment="Center" HorizontalAlignment="Center" TextAlignment="Center" Foreground="White" Background="Transparent" Width="500" MinWidth="300" Margin="10,0,0,0" Opacity="0.7"/>
<TextBox x:Name="DosyaİhtivaEdenDizin" CaretBrush="White" Foreground="White" Background="Transparent" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" VerticalAlignment="Center" HorizontalAlignment="Center" MinHeight="40" BorderThickness="1" BorderBrush="White" Width="500" MinWidth="300" Margin="10,0,0,0" GotFocus="DosyaİhtivaEdenDizin_GotFocus" LostFocus="DosyaİhtivaEdenDizin_LostFocus"/>
</Grid>

C#:

    #region DosyaİhtivaEdenDizin
    private void DosyaİhtivaEdenDizin_GotFocus(object sender, RoutedEventArgs e)
    {
        if (DosyaİhtivaEdenDizin.Text.Length == 0)
        {
            DosyaİhtivaEdenDizinYansıması.Text = "";
        }
    }

    private void DosyaİhtivaEdenDizin_LostFocus(object sender, RoutedEventArgs e)
    {
        if (DosyaİhtivaEdenDizin.Text.Length == 0)
        {
            DosyaİhtivaEdenDizinYansıması.Text = "Hedef Dizin Belirtin";
        }
    }
    #endregion

这是一个演示如何在WPF中创建水印文本框的示例:

<Window x:Class="WaterMarkTextBoxDemo.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WaterMarkTextBoxDemo"
    Height="200" Width="400">

    <Window.Resources>

        <SolidColorBrush x:Key="brushWatermarkBackground" Color="White" />
        <SolidColorBrush x:Key="brushWatermarkForeground" Color="LightSteelBlue" />
        <SolidColorBrush x:Key="brushWatermarkBorder" Color="Indigo" />

        <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter" />
        <local:TextInputToVisibilityConverter x:Key="TextInputToVisibilityConverter" />

        <Style x:Key="EntryFieldStyle" TargetType="Grid" >
            <Setter Property="HorizontalAlignment" Value="Stretch" />
            <Setter Property="VerticalAlignment" Value="Center" />
            <Setter Property="Margin" Value="20,0" />
        </Style>

    </Window.Resources>


    <Grid Background="LightBlue">

        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>

        <Grid Grid.Row="0" Background="{StaticResource brushWatermarkBackground}" Style="{StaticResource EntryFieldStyle}" >
            <TextBlock Margin="5,2" Text="This prompt dissappears as you type..." Foreground="{StaticResource brushWatermarkForeground}"
                       Visibility="{Binding ElementName=txtUserEntry, Path=Text.IsEmpty, Converter={StaticResource BooleanToVisibilityConverter}}" />
            <TextBox Name="txtUserEntry" Background="Transparent" BorderBrush="{StaticResource brushWatermarkBorder}" />
        </Grid>

        <Grid Grid.Row="1" Background="{StaticResource brushWatermarkBackground}" Style="{StaticResource EntryFieldStyle}" >
            <TextBlock Margin="5,2" Text="This dissappears as the control gets focus..." Foreground="{StaticResource brushWatermarkForeground}" >
                <TextBlock.Visibility>
                    <MultiBinding Converter="{StaticResource TextInputToVisibilityConverter}">
                        <Binding ElementName="txtUserEntry2" Path="Text.IsEmpty" />
                        <Binding ElementName="txtUserEntry2" Path="IsFocused" />
                    </MultiBinding>
                </TextBlock.Visibility>
            </TextBlock>
            <TextBox Name="txtUserEntry2" Background="Transparent" BorderBrush="{StaticResource brushWatermarkBorder}" />
        </Grid>

    </Grid>

</Window>

TextInputToVisibilityConverter定义为:

using System;
using System.Windows.Data;
using System.Windows;

namespace WaterMarkTextBoxDemo
{
    public class TextInputToVisibilityConverter : IMultiValueConverter
    {
        public object Convert( object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture )
        {
            // Always test MultiValueConverter inputs for non-null
            // (to avoid crash bugs for views in the designer)
            if (values[0] is bool && values[1] is bool)
            {
                bool hasText = !(bool)values[0];
                bool hasFocus = (bool)values[1];

                if (hasFocus || hasText)
                    return Visibility.Collapsed;
            }

            return Visibility.Visible;
        }


        public object[] ConvertBack( object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture )
        {
            throw new NotImplementedException();
        }
    }
}

注意:这不是我的代码。我是在这里找到的，但我认为这是最好的方法。

这个库有水印。

Nuget包

示例用法:

<TextBox adorners:Watermark.Text="Write something here" 
         adorners:Watermark.TextStyle="{StaticResource AdornerTextStyle}"
         adorners:Watermark.VisibleWhen="EmptyAndNotKeyboardFocused"/>

使用风格的简单解决方案:

<TextBox>
    <TextBox.Style>
        <Style TargetType="TextBox" xmlns:sys="clr-namespace:System;assembly=mscorlib">
            <Style.Resources>
                <VisualBrush x:Key="CueBannerBrush" AlignmentX="Left" AlignmentY="Center" Stretch="None">
                    <VisualBrush.Visual>
                        <Label Content="MM:SS:HH AM/PM" Foreground="LightGray" />
                    </VisualBrush.Visual>
                </VisualBrush>
            </Style.Resources>
            <Style.Triggers>
                <Trigger Property="Text" Value="{x:Static sys:String.Empty}">
                    <Setter Property="Background" Value="{StaticResource CueBannerBrush}" />
                </Trigger>
                <Trigger Property="Text" Value="{x:Null}">
                    <Setter Property="Background" Value="{StaticResource CueBannerBrush}" />
                </Trigger>
                <Trigger Property="IsKeyboardFocused" Value="True">
                    <Setter Property="Background" Value="White" />
                </Trigger>
            </Style.Triggers>
        </Style>
    </TextBox.Style>
</TextBox>

伟大的解决方案:

https://code.msdn.microsoft.com/windowsdesktop/In-place-hit-messages-for-18db3a6c

namespace PlaceholderForRichTexxBoxInWPF
{
public MainWindow()
        {
            InitializeComponent();
            Application.Current.MainWindow.WindowState = WindowState.Maximized;// maximize window on load

            richTextBox1.GotKeyboardFocus += new KeyboardFocusChangedEventHandler(rtb_GotKeyboardFocus);
            richTextBox1.LostKeyboardFocus += new KeyboardFocusChangedEventHandler(rtb_LostKeyboardFocus);
            richTextBox1.AppendText("Place Holder");
            richTextBox1.Foreground = Brushes.Gray;
        }
 private void rtb_GotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
        {
            if (sender is RichTextBox)
            {
                TextRange textRange = new TextRange(richTextBox1.Document.ContentStart, richTextBox1.Document.ContentEnd); 

                if (textRange.Text.Trim().Equals("Place Holder"))
                {
                    ((RichTextBox)sender).Foreground = Brushes.Black;
                    richTextBox1.Document.Blocks.Clear();
                }
            }
        }


        private void rtb_LostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
        {
            //Make sure sender is the correct Control.
            if (sender is RichTextBox)
            {
                //If nothing was entered, reset default text.
                TextRange textRange = new TextRange(richTextBox1.Document.ContentStart, richTextBox1.Document.ContentEnd); 

                if (textRange.Text.Trim().Equals(""))
                {
                    ((RichTextBox)sender).Foreground = Brushes.Gray;
                    ((RichTextBox)sender).AppendText("Place Holder");
                }
            }
        }
}