How to use a IValueConverter multiple times with different values in WPF?

Question

I have a WPF application where I need to show a rectangle at the top of the title bar. But the Rectangle should not cover the whole title bar. For this purpose I use a IValueConverter which gives me the exact output which I want. I do a data binding with the width of that Rectangle and use the converter there.

My problem is I need to use another Rectangle on that title bar but I except different value from that converter. Because this time Rectangle size is very small. Some people suggest me to use converter parameter. I use that but I don't get any value from it.

Here is my IValueConverter in C# :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Data;
using System.Globalization;

namespace WpfApp1
{
   public class WpConverter : IValueConverter
    {

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return double.Parse(value.ToString()) - 142;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }
}

Here is the Xaml code of my Rectangle:

 <Rectangle Fill="Yellow" Stroke="{x:Null}" Grid.Row="0" HorizontalAlignment="Stretch" Width="{Binding Path=ActualWidth, ElementName=xp, Converter={StaticResource WpConverter}}"  VerticalAlignment="Top" Height="1"  Margin="-140,0,0,0"  x:Name="top" PreviewMouseDown="Resize" MouseMove="DisplayResizeCursor" />

I need to use another similar Rectangle But If I use the same converter I get the same values. The main goal is to change this line return double.Parse(value.ToString()) - 142;

the another way I found is to declare another IValueConverter with different values. But that pretty awkward. I need to do something using converter parameter.

Answer 1

HU,
you can use ConverterParameter:

<Rectangle Width="{Binding Path=ActualWidth, ElementName=xp, Converter={StaticResource WpConverter}, ConverterParameter=142}"  ...

and converter:

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
  double disp;
  if (parameter == null || !double.TryParse(parameter.ToString(), out disp)) disp =142;
  return double.Parse(value.ToString()) - disp;
}

public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
  throw new NotImplementedException();
}