参数化样式以在WPF文本框中显示提示文本

Question

我正在尝试创建用于在WPF文本框中显示提示文本的参数化样式。原始代码取自this SO question（我向HintText属性添加了绑定）。它确实没有绑定功能。但是当我将HintText绑定到Content的Label时没有运气：

    <Window.Resources>
    <Style x:Key="HintTextStyle" TargetType="{x:Type TextBox}">
        <Style.Resources>
            <VisualBrush x:Key="CueBannerBrush" AlignmentX="Left" AlignmentY="Center" Stretch="None">
                <VisualBrush.Visual>
                    <Label Content="{Binding Path=(local:HintTextProperties.HintText), RelativeSource={RelativeSource AncestorType={x:Type TextBox}}}"
                           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>
        </Style.Triggers>
    </Style>
</Window.Resources>

<Grid>
    <TextBox Height="23" Margin="100,100" TextWrapping="Wrap" Text="" VerticalAlignment="Top" Width="120"
             local:HintTextProperties.HintText="Some hint text"
             Style="{DynamicResource HintTextStyle}" />

    <Button Content="Button" HorizontalAlignment="Left" Margin="361,166,0,0" VerticalAlignment="Top" Width="75"/>
</Grid>

依赖项属性：

public class HintTextProperties
{
    public static string GetHintText(DependencyObject obj)
    {
       return (string)obj.GetValue(HintTextProperty);
    }

    public static void SetHintText(DependencyObject obj, string value)
    {
        obj.SetValue(HintTextProperty, value);
    }

    public static readonly DependencyProperty HintTextProperty =
        DependencyProperty.RegisterAttached(
        "HintText",
        typeof(string),
        typeof(HintTextProperties),
        new FrameworkPropertyMetadata(""));
}    

此代码有什么问题？

Answer 1

您可以使用此：

   <Style x:Key="placeHolder" TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type TextBox}">
                <Grid>
                    <TextBox Text="{Binding Path=Text,
                                            RelativeSource={RelativeSource TemplatedParent}, 
                                            Mode=TwoWay,
                                            UpdateSourceTrigger=PropertyChanged}"
                             x:Name="textSource" 
                             Background="Transparent" 
                             Panel.ZIndex="2" />
                    <TextBox Text="{TemplateBinding Tag}" Background="{TemplateBinding Background}" Panel.ZIndex="1">
                        <TextBox.Style>
                            <Style TargetType="{x:Type TextBox}">
                                <Setter Property="Foreground" Value="Transparent"/>
                                <Style.Triggers>
                                    <DataTrigger Binding="{Binding Path=Text, Source={x:Reference textSource}}" Value="">
                                        <Setter Property="Foreground" Value="LightGray"/>
                                    </DataTrigger>
                                </Style.Triggers>
                            </Style>
                        </TextBox.Style>
                    </TextBox>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

用法：

<TextBox Style="{StaticResource placeHolder}" Tag="Name of customer" Width="150" Height="24"/>

Reference