How to make Converters with bindable ConverterParameters? - wpf

Question

Most converters take no parameters, or one fixed parameter, and are easy to bind to:
<local:MyConverter x:Key="MyConverterInstance" />
<TextBox Text="{Binding Path=MyTime,
Converter={StaticResource MyConverterInstance},
ConverterParameter='yyyy/MM/dd'}" />
But if I want that format to be a dynamic property that the user can change, I can't do something like this, right?:
<TextBox Text="{Binding Path=MyTime,
Converter={StaticResource MyConverterInstance},
ConverterParameter={Binding Path=UserFormat}}" />
So my only option is to define a DependencyProperty on MyConverter for binding. But my converter definition is a StaticResource. I can't go
<local:MyConverter x:Key="MyConverterInstance"
Format="{Binding Path=UserFormat}"/>
because there's no DataContext on StaticResources. How can I set this up?

Answer 1

You cannot bind to a converterparameter but you can use Multibinding instead.
For example: http://www.switchonthecode.com/tutorials/wpf-tutorial-using-multibindings
or How to simply bind this to ConverterParameter?
(Alain) So just to translate that linked answer into something that matches this question:
<TextBlock>
<TextBlock.Resources>
<local:MyConverter x:Key="MyConverterInstance" />
</TextBlock.Resources>
<TextBlock.Text>
<MultiBinding Converter="{StaticResource converter}">
<Binding Path="MyTime" />
<Binding Path="UserFormat" />
</MultiBinding>
</TextBlock.Text>
</TextBlock>
public class MyConverter : IMultiValueConverter
{
public object Convert(object[] values, Type targetType, object parameter,
System.Globalization.CultureInfo culture)
{
DateTime time = (DateTime)values[0];
string format = values[1].ToString();
return time.ToString(format);
}
public object[] ConvertBack(object value, Type[] targetTypes, object parameter,
System.Globalization.CultureInfo culture)
{
throw new NotImplementedException();
}
}