Question

I have the following converter defined (C#):

class BodyValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        string s = value.ToString();
        int prefixLength;
        if (!int.TryParse(parameter.ToString(), out prefixLength))
            return s;
        return s.Substring(0, prefixLength);
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

This will start at the start of the string being passed and will return the amount of characters I specify as a parameter.

In my XAML I have instanced the converter:

<local:BodyValueConverter x:Key="BodyValueConverter"/>

In attempting to use this converter in a textblock I get an error:

<DataTemplate x:Key="AppointmentTemplate">
    <StackPanel Orientation="Horizontal">
        <TextBlock Text="{Binding Subject}"></TextBlock>
        <TextBlock Text="{Binding Path=Subject, Converter={StaticResource BodyValueConverter}, ConverterParameter=1}"></TextBlock>
    </StackPanel>
</DataTemplate>

The error is:

XAMLParseException: Provide value on ‘System.Windows.Markup.StaticResourceHolder’ threw an exception.

The first textblock works fine to display subject. The 2nd line is what gives me the exception.

Answer 1

What’s the order of your objects in your XAML?

The Converter has to be defined prior to actually being used, so be sure your <Converter> is above your <DataTemplate> in your Resources

Another alternative is to switch to using a DynamicResource instead of a StaticResource, since a DynamicResource is evaluated when it is needed, not when the XAML is loaded