Question

I have a custom usercontrol with that code:

public partial class AudioControl : UserControl
{
    public AudioControl()
    {
        InitializeComponent();
        Value = 0.1;
        DataContext = this;
    }

    public event RoutedPropertyChangedEventHandler<double> ValueChanged = delegate { };

    public int TextWidth
    {
        get { return (int)GetValue(TextWidthProperty); }
        set { SetValue(TextWidthProperty, value); }
    }

    public int SliderWidth
    {
        get { return (int)GetValue(SliderWidthProperty); }
        set { SetValue(SliderWidthProperty, value); }
    }

    public string Header
    {
        get { return (string)GetValue(TextBlock.TextProperty); }
        set { SetValue(TextBlock.TextProperty, value); }
    }

    //public double Value
    //{
    //    get { return (double)GetValue(Slider.ValueProperty); }
    //    set { SetValue(Slider.ValueProperty, value); }
    //}

    public double Value
    {
        get {
            return (double)GetValue(ValueProperty); 
        }
        set { 
            SetValue(ValueProperty, value);
        }
    }

    public static readonly DependencyProperty ValueProperty =
        DependencyProperty.Register("Value", typeof(double), typeof(AudioControl), new UIPropertyMetadata(0));

    public static readonly DependencyProperty TextWidthProperty =
        DependencyProperty.Register("TextWidth", typeof(int), typeof(AudioControl), new UIPropertyMetadata(0));

    public static readonly DependencyProperty SliderWidthProperty =
        DependencyProperty.Register("SliderWidth", typeof(int), typeof(AudioControl), new UIPropertyMetadata(0));

    private void Slider_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
    {
        ValueChanged(this, e);
    }
}

And this XAML:

<UserControl x:Class="Controller.Audio.AudioControl"
         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:Audio="clr-namespace:Controller.Audio"
         mc:Ignorable="d" 
         d:DesignHeight="23" d:DesignWidth="500" x:Name="audioControl">
<UserControl.Resources>
    <Audio:DoubleToIntConverter x:Key="doubleToInt"/>
</UserControl.Resources>
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="{Binding TextWidth}"/>
        <ColumnDefinition Width="40"/>
        <ColumnDefinition Width="{Binding SliderWidth}"/>
    </Grid.ColumnDefinitions>

    <Label x:Name="txtBlock" Margin="0,0,10,0">
        <Binding Path="Header"/>
    </Label>
    <Label Grid.Column="1" Content="{Binding ElementName=slider, Path=Value, Converter={StaticResource doubleToInt}}"/>
    <Slider x:Name="slider" Grid.Column="2" Style="{StaticResource Office2010SilverSliderStyle}" 
            Value="{Binding Path=Value, ElementName=audioControl}" Minimum="0.0" Maximum="1.0" LargeChange="0.25" TickFrequency="0.01" ValueChanged="Slider_ValueChanged"/>
</Grid>

So if i start it I get an exception that something with the value binding is wrong. I also tried the commented version (the value-Property). There is no exception but if i set the value of that property my slider does not change.

Does anyone has any idea why? I ve never done something like that 🙁

Answer 1

There’s an error in the following dependency property declaration:

public static readonly DependencyProperty ValueProperty =
    DependencyProperty.Register("Value", typeof(double), typeof(AudioControl), new UIPropertyMetadata(0));

The problem here is that you’re defining the dependency property to be of type double, but giving it a default value 0 that is an int. Try changing 0 to 0.0.

I ran your code and encountered an exception. The innermost exception contained the following message:

Default value type does not match type of property ‘Value’.

I changed the 0 in the line above to 0.0 and the problem went away.