UserControl中的依赖项属性：值不是为dp属性注册的正确类型

Question

i created a user control with some dependency properties. When i try to add the control to a window i get kind of a blank failure screen.

The inner most exception says : "value was not the correct type as registered for the dp property" (i hope this is the correct Translation - found it here: https://msdn.microsoft.com/de-de/library/ms597473(v=vs.110).aspx )

I would have translated it into " the Standard value type does not correspont with the type of the property "LabelColor".

here is the c# code of the control:

namespace HexButton
{
public partial class HexButtonControl : UserControl
{

    #region Dependency Properties

    #region LabelText

    /// <summary>
    /// Gets or sets the LabelText which is displayed next to the (unit-)rectangle
    /// </summary>
    public string LabelText
    {
        get { return (string)GetValue(LabelTextProperty); }
        set { SetValue(LabelTextProperty, value); }
    }

    /// <summary>
    /// Identified the LabelText dependency property
    /// </summary>
    public static readonly DependencyProperty LabelTextProperty =
        DependencyProperty.Register("LabelText", typeof(string),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion
    #region LabelColor

    /// <summary>
    /// Gets or sets the LabelColor (background) which is displayed next to the (unit-)rectangle
    /// </summary>
    public Brush LabelColor
    {
        get { return (Brush)GetValue(LabelColorProperty); }
        set { SetValue(LabelColorProperty, value); }
    }

    /// <summary>
    /// Identified the LabelColor dependency property
    /// </summary>
    public static readonly DependencyProperty LabelColorProperty =
        DependencyProperty.Register("LabelColor", typeof(Brush),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion

    #region RectangleBrush

    /// <summary>
    /// Gets or sets the Brush which is used to fill the (unit-)rectangle within the hexagon
    /// </summary>
    public Brush RectangleBrush
    {
        get { return (Brush)GetValue(RectangleBrushProperty); }
        set { SetValue(RectangleBrushProperty, value); }
    }

    /// <summary>
    /// Identified the RectangleBrush dependency property
    /// </summary>
    public static readonly DependencyProperty RectangleBrushProperty =
        DependencyProperty.Register("RectangleBrush", typeof(Brush),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion

    #region HexBackground

    /// <summary>
    /// Gets or sets the Brush which is used to fill the background of the hexagon
    /// </summary>
    public Brush HexBackground
    {
        get { return (Brush)GetValue(HexBackgroundProperty); }
        set { SetValue(HexBackgroundProperty, value); }
    }

    /// <summary>
    /// Identified the HexBackground dependency property
    /// </summary>
    public static readonly DependencyProperty HexBackgroundProperty =
        DependencyProperty.Register("HexBackground", typeof(Brush),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion
    #region HexBorderColor

    /// <summary>
    /// Gets or sets the Brush which is used to draw the border of the hexagon
    /// </summary>
    public Brush HexBorderColor
    {
        get { return (Brush)GetValue(HexBorderColorProperty); }
        set { SetValue(HexBorderColorProperty, value); }
    }

    /// <summary>
    /// Identified the HexBorderColor dependency property
    /// </summary>
    public static readonly DependencyProperty HexBorderColorProperty =
        DependencyProperty.Register("HexBorderColor", typeof(Brush),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion              
    #region HexStokeDashArray

    /// <summary>
    /// Gets or sets the the StrokeDashArray for the border of the Hhxagon
    /// </summary>
    public DoubleCollection HexStokeDashArray
    {
        get { return (DoubleCollection)GetValue(HexStokeDashArrayProperty); }
        set { SetValue(HexStokeDashArrayProperty, value); }
    }

    /// <summary>
    /// Identified the HexStokeDashArray dependency property
    /// </summary>
    public static readonly DependencyProperty HexStokeDashArrayProperty =
        DependencyProperty.Register("HexStokeDashArray", typeof(DoubleCollection),
          typeof(HexButtonControl), new PropertyMetadata(""));

    #endregion

    #endregion

    public HexButtonControl()
    {            
        LayoutRoot.DataContext = this;
    }
}

public class HexModelObject
{
    private string _labelText;
    public string LabelText
    {
        get { return _labelText; }
        set
        {
            _labelText = value;
            OnPropertyChanged("LabelText");
        }
    }

    private Brush _labelColor;
    public Brush LabelColor
    {
        get { return _labelColor; }
        set
        {
            _labelColor = value;
            OnPropertyChanged("LabelColor");
        }
    }

    private Brush _rectangleBrush;
    public Brush RectangleBrush
    {
        get { return _rectangleBrush; }
        set
        {
            _rectangleBrush = value;
            OnPropertyChanged("RectangleBrush");
        }
    }

    private Brush _hexBackground;
    public Brush HexBackground
    {
        get { return _hexBackground; }
        set
        {
            _hexBackground = value;
            OnPropertyChanged("HexBackground");
        }
    }

    private Brush _hexBorderColor;
    public Brush HexBorderColor
    {
        get { return _hexBorderColor; }
        set
        {
            _hexBorderColor = value;
            OnPropertyChanged("HexBorderColor");
        }
    }

    private DoubleCollection _hexStrokeDashArray;
    public DoubleCollection HexStrokeDashArray
    {
        get { return _hexStrokeDashArray; }
        set
        {
            _hexStrokeDashArray = value;
            OnPropertyChanged("HexStrokeDashArray");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}
}

and the xaml of the control:

<UserControl x:Class="HexButton.HexButtonControl"
         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" 
         Height="91" Width="104">
         <!--d:DesignHeight="91" d:DesignWidth="104">-->
<Canvas x:Name="LayoutRoot">
    <Polygon Points="27,2 77,2 102,45 77,89 27,89 2,45"
             StrokeThickness="4"
             Fill="{Binding Path=HexBackground}"
             Stroke="{Binding Path=HexBorderColor}"
             StrokeDashArray="{Binding Path=HexStokeDashArray}"/>
    <Rectangle
             Height="70"
             Width="48"
             Fill="{Binding Path=RectangleBrush}"
             Canvas.Left="28"
             Canvas.Top="10"
     />
    <Label 
        Height="24" 
        Width="14"
        Padding="0"
        FontSize="18"
        FontWeight="Bold"            
        Background="{Binding Path=LabelColor}"
        Canvas.Left="80" 
        Canvas.Top="31"
        Content="{Binding Path=LabelText}" />        
</Canvas>

In the main window its just:

<Window x:Class="HexButton.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525"
    xmlns:myControls="clr-namespace:HexButton">
<Grid Name="myGrid">
    <myControls:HexButtonControl x:Name="UC1"
        HexBackground="AliceBlue" HexBorderColor="Black" RectangleBrush="Green" LabelColor="Beige" LabelText="asdf">
    </myControls:HexButtonControl>
</Grid>
</Window>

I tied to out comment the LabelColor dependency property, but then the failure occurs for RectangleBrush so i think its a problem with the Brush . I double checked the properties - the Background property of a Label has the type (System.Windows.Media.) Brush . Maybe this is because Brush has no default value? If so how do i set it?

I found out that removing the PropertyMetadata helps for the depedency property issues. But then i get another Exception in the constuctor with "LayoutRoot.DataContext = this;" which is a NullReferenceException for the LayoutRoot .

I created my HexButtonControl following http://blog.scottlogic.com/2012/02/06/a-simple-pattern-for-creating-re-useable-usercontrols-in-wpf-silverlight.html

Answer 1

In your dependency property, the new PropertyMetadata() argument is the default value to the property. Your property is of the type Brush, and you're passing a string as the default value. This mistake happens in other properties too. Try this, or another brush you like:

public static readonly DependencyProperty LabelColorProperty =
    DependencyProperty.Register("LabelColor", typeof(Brush),
      typeof(HexButtonControl), new PropertyMetadata(Brushes.Black));

Edit: Sorry, had missed the last part. Appears to me that you're missing the InitializeComponent(); call in your constructor, before the line you set the DataContext:

public HexButtonControl()
{   
    InitializeComponent();
    LayoutRoot.DataContext = this;
}