Binding problem when creating custom ProgressBar - wpf

Question

<UserControl x:Class="WpfApplication2.ProgressBar"
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"
d:DesignHeight="300" d:DesignWidth="300">
<Grid>
<ProgressBar Minimum="0" Maximum="1" Value="0.5" LargeChange="0.1" SmallChange="0.01" Margin="2,2,12,2" Height="22">
<ProgressBar.Template>
<ControlTemplate>
<Border BorderThickness="2" BorderBrush="Black">
<Rectangle>
<Rectangle.Fill>
<LinearGradientBrush StartPoint="0,0">
<LinearGradientBrush.EndPoint>
<Point Y="0" X="{Binding RelativeSource={RelativeSource AncestorType={x:Type ProgressBar}}, Path=ProgressBar.Value}"/>
</LinearGradientBrush.EndPoint>
<GradientStop Color="Transparent" Offset="1.01"/>
<GradientStop Color="#FF0000" Offset="1.0"/>
<GradientStop Color="#FFFF00" Offset="0.50"/>
<GradientStop Color="#00FF00" Offset="0.0"/>
</LinearGradientBrush>
</Rectangle.Fill>
</Rectangle>
</Border>
</ControlTemplate>
</ProgressBar.Template>
</ProgressBar>
<TextBlock Text="50%" HorizontalAlignment="Center" VerticalAlignment="Center" />
</Grid>
</UserControl>
I get error: "A 'Binding' cannot be set on the 'X' property of type 'Point'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject."
Is there any clean workaround?

Answer 1

Since Point.X isn't a Dependency Property you can't bind it to something. You could bind the EndPointProperty though, and use a Converter that creates the Point for you. It could take the Y value as parameter for example
Xaml
<LinearGradientBrush.EndPoint>
<Binding RelativeSource="{RelativeSource AncestorType={x:Type ProgressBar}}"
Path="Value"
Converter="{StaticResource PointXConverter}"
ConverterParameter="0"/>
</LinearGradientBrush.EndPoint>
PointXConverter
public class PointXConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
double progressBarValue = (double)value;
double yValue = System.Convert.ToDouble(parameter);
return new Point(progressBarValue, yValue);
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}
Note: Probably not related to your question but if you would need to bind Y as well, you can use a MultiBinding like this
<LinearGradientBrush.EndPoint>
<MultiBinding Converter="{StaticResource PointConverter}">
<Binding RelativeSource="{RelativeSource AncestorType={x:Type ProgressBar}}"
Path="Value"/>
<Binding RelativeSource="{RelativeSource AncestorType={x:Type ProgressBar}}"
Path="Value"/>
</MultiBinding>
</LinearGradientBrush.EndPoint>
PointConverter
public class PointConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
double xValue = (double)values[0];
double yValue = (double)values[1];
return new Point(xValue, yValue);
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}