c# - 依赖属性和自定义文本框的问题

Question

我想创建自定义文本框(其中将包含简单的水印/提示文本)并且我遇到了依赖属性的一些问题。我的自定义类继承自 TextBox 类并包含两个文件 (.xaml .cs)C#代码文件非常简单:

public partial class HintTextBox : TextBox
{
    public string HintText
    {
        get { return (string)GetValue(HintTextProperty); }
        set { SetValue(HintTextProperty, value); }
    }
    public static readonly DependencyProperty HintTextProperty =
        DependencyProperty.Register(
            "HintText",
            typeof(string),
            typeof(HintTextBox),
            new FrameworkPropertyMetadata(string.Empty));
}

.xaml 文件包含显示/隐藏水印的代码

<local:HintTextBox xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:local="clr-namespace:Ribes.Client.GUI"
                xmlns:sys="clr-namespace:System;assembly=mscorlib">
<local:HintTextBox.Style>
    <Style TargetType="{x:Type local:HintTextBox}">
        <Style.Resources>
            <VisualBrush x:Key="CueBannerBrush" AlignmentX="Left" AlignmentY="Center" Stretch="None">
                <VisualBrush.Visual>
                    <Label Content="{Binding HintText, ElementName=local:HintTextBox}" Foreground="LightGray" />
                </VisualBrush.Visual>
            </VisualBrush>
        </Style.Resources>
        <Style.Triggers><!-- triggers changing content of control --></Style.Triggers>
    </Style>
</local:HintTextBox.Style>

我正在尝试获取我的 HintTextBox 的简单用法:

<local:HintTextBox HintText="hint text"></local:HintTextBox>

而且它不起作用。在线创建刹车点后:

SetValue(HintTextProperty, value);

代码从未达到。 TextBox 的继承属性(文本、背景)工作正常:

<local:HintTextBox Text="example text" Background="Yellow"></local:HintTextBox>

我们可以看到正确的黄色文本框，里面有“示例文本”。

有人知道我的 DP 有什么问题吗？

敬礼网易

Answer 1

您需要使用 Generic.xaml 来设置文本框的样式。为此，您需要在静态构造函数中覆盖 DefaultStyleKey。

HintTextBox.cs

public class HintTextBox : TextBox
{
    public static DependencyProperty HintTextProperty = DependencyProperty.Register("HintText", typeof(string), typeof(HintTextBox));

    public string HintText
    {
        get { return (string)GetValue(HintTextProperty); }
        set { SetValue(HintTextProperty, value); }
    }

    static HintTextBox()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(HintTextBox), new FrameworkPropertyMetadata(typeof(HintTextBox)));
    }
}

Generic.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                    xmlns:Local="Ribes.Client.GUI">

    <!-- Describes how to style a HintTextBox -->
    <Style x:Key="{x:Type Local:HintTextBox}" BasedOn="{StaticResource {x:Type TextBox}}" TargetType="{x:Type Local:HintTextBox}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Local:HintTextBox}">
                    <Border x:Name="Border" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}"
                            BorderThickness="{TemplateBinding BorderThickness}" SnapsToDevicePixels="True">
                        <Grid x:Name="LayoutGrid">
                            <ScrollViewer x:Name="PART_ContentHost" Margin="2" />
                            <Label x:Name="HintText" Content="{Binding HintText, RelativeSource={RelativeSource TemplatedParent}}"
                                   FontStyle="Italic" Margin="2" Padding="2,0,0,0" />
                        </Grid>
                    </Border>
                    <ControlTemplate.Triggers>
                        <Trigger Property="HasText" Value="True">
                            <Setter Property="Visibility" TargetName="HintText" Value="Hidden" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>