DependencyProperty typeof GridLength没有传递值"Auto"到自定

我正在构建一个CustomControl与一些DependencyProperty的。这是一个用于浏览路径的简单控件，包含一个标签、一个文本框和一个按钮。

我想分别设置标签、文本框和按钮的宽度。所以我为它们添加了一些DependencyProperty。

namespace DDD.AutoRadio.General.UserControls
{
/// <summary>
/// Interaction logic for PathBrowser.xaml
/// </summary>
public partial class PathBrowser : UserControl
{
    public PathBrowser() { InitializeComponent(); }
    public static DependencyProperty labelContent = DependencyProperty.Register("LabelContent", typeof(string), typeof(PathBrowser));
    public static DependencyProperty labelWidth = DependencyProperty.Register("LabelWidth", typeof(GridLength), typeof(PathBrowser),
        new FrameworkPropertyMetadata(GridLength.Auto, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
    public static DependencyProperty buttonContent = DependencyProperty.Register("ButtonContent", typeof(string), typeof(PathBrowser),
        new FrameworkPropertyMetadata("Blader",FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
    public static DependencyProperty buttonWidth = DependencyProperty.Register("ButtonWidth", typeof(GridLength), typeof(PathBrowser),
        new FrameworkPropertyMetadata(default(GridLength), FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
    public static DependencyProperty textBoxText = DependencyProperty.Register("UrlPath", typeof(string), typeof(PathBrowser),
        new FrameworkPropertyMetadata("", FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,null,null,false,UpdateSourceTrigger.PropertyChanged));
    public static DependencyProperty textBoxWidth = DependencyProperty.Register("UrlPathWidth", typeof(GridLength), typeof(PathBrowser),
        new FrameworkPropertyMetadata(GridLength.Auto, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
    public static DependencyProperty typeBrowser = DependencyProperty.Register("TypeBrowser", typeof(BrowserType), typeof(PathBrowser),
        new FrameworkPropertyMetadata(BrowserType.Directory, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));
    public enum BrowserType { Directory,File}
    public string LabelContent
    {
        get { return (string)GetValue(labelContent); }
        set { SetValue(labelContent, value); }
    }
    public GridLength LabelWidth
    {
        get { return (GridLength)GetValue(labelWidth); }
        set { SetValue(labelWidth, value); }
    }
    public string ButtonContent
    {
        get { return (string)GetValue(buttonContent); }
        set { SetValue(buttonContent, value); }
    }
    public GridLength ButtonWidth
    {
        get { return (GridLength)GetValue(buttonWidth); }
        set { SetValue(buttonWidth, value); }
    }
    public string UrlPath
    {
        get { return (string)GetValue(textBoxText); }
        set { SetValue(textBoxText, value); }
    }
    public GridLength UrlPathWidth
    {
        get { return (GridLength)GetValue(textBoxWidth); }
        set { SetValue(textBoxWidth, value); }
    }
    public BrowserType TypeBrowser
    {
        get { return (BrowserType)GetValue(typeBrowser); }
        set { SetValue(typeBrowser, value); }
    }
    private void Button_Click(object sender, RoutedEventArgs e)
    {
        if (TypeBrowser == BrowserType.Directory)
        {
            System.Windows.Forms.FolderBrowserDialog op = new System.Windows.Forms.FolderBrowserDialog();
            op.SelectedPath = UrlPath;
            if (op.ShowDialog() == System.Windows.Forms.DialogResult.OK)
            {
                UrlPath = System.IO.Path.GetFullPath(op.SelectedPath);
            }
        }
        if (TypeBrowser==BrowserType.File)
        {
            System.Windows.Forms.OpenFileDialog fd = new System.Windows.Forms.OpenFileDialog();
            try { fd.InitialDirectory = System.IO.Path.GetDirectoryName(UrlPath); } catch { }
            fd.Multiselect = false;
            if (fd.ShowDialog()== System.Windows.Forms.DialogResult.OK)
            {
                UrlPath = System.IO.Path.GetFullPath(fd.FileName);
            }
        }
    }
}

下面是我的CustomControl的XML代码:

<UserControl x:Class="DDD.AutoRadio.General.UserControls.PathBrowser"
         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" 
         xmlns:local="clr-namespace:DDD.AutoRadio.General.UserControls"
         mc:Ignorable="d" Name="Root"
         d:DesignHeight="24" d:DesignWidth="300">
<DockPanel LastChildFill="True">
    <Label DockPanel.Dock="Left" Padding="2" Margin="3" Content="{Binding LabelContent,ElementName=Root}"
           Width="{Binding LabelWidth,ElementName=Root}"/>
    <Button DockPanel.Dock="Right" Padding="2" Margin="3" Content="{Binding ButtonContent,ElementName=Root}"
            Width="{Binding ButtonWidth,ElementName=Root}" Click="Button_Click"/>
    <TextBox Padding="2" Margin="3" Text="{Binding UrlPath,ElementName=Root}" Width="{Binding UrlPathWidth,ElementName=Root}" />
</DockPanel>
</UserControl>

所有绑定的DependencyProperty类型string工作完美，但宽度属性的值保持"auto"。我用转换器进行了测试，并将值"200"设置为DP"LabelWidth"作为{200}(当我在转换器中击中断点时鼠标移到"值"上时)，但标签的宽度不会改变。当我将GridLength更改为Double时，我不能将其设置为Auto

[TypeConverterAttribute(typeof(LengthConverter))]
public Double LabelWidth
{
    get { return (Double)GetValue(labelWidth); }
    set { SetValue(labelWidth, value); }
}

public static DependencyProperty labelWidth = DependencyProperty.Register("LabelWidth", typeof(Double), typeof(PathBrowser),
    new FrameworkPropertyMetadata(Double.NaN, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

<local:PathBrower LabelWidth="Auto" />

public static readonly DependencyProperty ItemHeightProperty = 
  DependencyProperty.Register(
    "ItemHeight", 
    typeof (GridLength), 
    typeof (TreeViewItem), 
    new FrameworkPropertyMetadata(new GridLength(30)));
/// <summary>
/// Indique si un overlay est présent
/// </summary>
public GridLength ItemHeight
{
    get
    {
        return (GridLength)GetValue(ItemHeightProperty);
    }
    set
    {
        SetValue(ItemHeightProperty, value);
    }
}