Passing parameters to Value Converter

Sometimes we need to make two or more value converters those are very similar in logic with each other. One possible solution is to make as much converter as much implementations we need. Other solution is to pass parameter to the converter function and uses the ConverterParameter property class in Binding.

Here is a class diagram of IValueConverter.

Now lets make one converter class to convert double into Point. Here we are going to convert the current value of slider into point and and uses it as a starting point of linear gradient brush. We uses its parameter for forward and backward moment for starting and ending position of gradient. Here is implementation of our converter class.

  1: public class PointConverter : IValueConverter

  2: {

  3:     public object Convert(object value, Type targetType, 

  4:         object parameter, CultureInfo cultureInfo)

  5:     {

  6:         double currentValue = (double)value;

  7:         String direction = parameter as string;

  8: 

  9:         if (direction == "Forward")

 10:         {

 11:             Point point = new Point(currentValue, currentValue);

 12:             return point;

 13:         }

 14:         else if (direction == "Backward")

 15:         {

 16:             Point point = new Point(1 - currentValue, 1 - currentValue);

 17:             return point;

 18:         }

 19:         else

 20:             return null;

 21:     }

 22: 

 23:     public object ConvertBack(object value, Type targetType,

 24:         object parameter, CultureInfo cultureInfo)

 25:     {

 26:         throw new NotImplementedException();

 27:     }

 28: }

 29: 
We have to use the ConverterParameter property of binding class to pass parameter into the converter. Here is a piece of XAML code to pass parameter to our converter.
  1: <LinearGradientBrush 

  2: 	StartPoint="{Binding ElementName=slider, Path=Value, 

  3: 	Converter={StaticResource pointConverterObj},

  4: 	ConverterParameter='Forward'}"  

  5: 	EndPoint="{Binding ElementName=slider, Path=Value, 

  6: 	Converter={StaticResource pointConverterObj},

  7: 	ConverterParameter='Backward'}">

  8: 	<GradientStop Offset="0" Color="AliceBlue"/>

  9: 	<GradientStop Offset="1" Color="Blue"/>

 10: </LinearGradientBrush>

 11: 
Here we use ElementName to bind it with current value of Slider control. Here is complete XAML code of the program.
  1: <Window x:Class="WpfGradient.Window1"

  2:     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

  3:     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

  4:     xmlns:local="clr-namespace:WpfGradient"

  5:     Title="Linear Gradient" Height="300" Width="300">

  6:     <Window.Resources>

  7:         <local:PointConverter x:Key="pointConverterObj"/>

  8:     </Window.Resources>

  9:     <Grid>

 10:         <Grid.RowDefinitions>

 11:             <RowDefinition Height="4*"/>

 12:             <RowDefinition/>

 13:         </Grid.RowDefinitions>

 14:         <Rectangle Grid.Row="0" Name="rectangle" Margin="5">

 15:             <Rectangle.Fill>

 16:                 <LinearGradientBrush 

 17:                     StartPoint="{Binding ElementName=slider, Path=Value, 

 18:                     Converter={StaticResource pointConverterObj},

 19:                     ConverterParameter='Forward'}"  

 20:                     EndPoint="{Binding ElementName=slider, Path=Value, 

 21:                     Converter={StaticResource pointConverterObj},

 22:                     ConverterParameter='Backward'}">

 23:                     <GradientStop Offset="0" Color="AliceBlue"/>

 24:                     <GradientStop Offset="1" Color="Blue"/>

 25:                 </LinearGradientBrush>

 26:             </Rectangle.Fill>

 27:         </Rectangle>

 28:         <Slider Name="slider" Grid.Row="1" Margin="5" Minimum="0" Maximum="1" Value="0"/>

 29:     </Grid>

 30: </Window>

 31: 
Here is complete C# code of the program.
  1: using System;

  2: using System.Collections.Generic;

  3: using System.Linq;

  4: using System.Text;

  5: using System.Windows;

  6: using System.Windows.Controls;

  7: using System.Windows.Data;

  8: using System.Windows.Documents;

  9: using System.Windows.Input;

 10: using System.Windows.Media;

 11: using System.Windows.Media.Imaging;

 12: using System.Windows.Navigation;

 13: using System.Windows.Shapes;

 14: using System.Globalization;

 15: 

 16: namespace WpfGradient

 17: {

 18:     /// <summary>

 19:     /// Interaction logic for Window1.xaml

 20:     /// </summary>

 21:     public partial class Window1 : Window

 22:     {

 23:         public Window1()

 24:         {

 25:             InitializeComponent();

 26:         }

 27:     }

 28: 

 29:     public class PointConverter : IValueConverter

 30:     {

 31:         public object Convert(object value, Type targetType, 

 32:             object parameter, CultureInfo cultureInfo)

 33:         {

 34:             double currentValue = (double)value;

 35:             String direction = parameter as string;

 36: 

 37:             if (direction == "Forward")

 38:             {

 39:                 Point point = new Point(currentValue, currentValue);

 40:                 return point;

 41:             }

 42:             else if (direction == "Backward")

 43:             {

 44:                 Point point = new Point(1 - currentValue, 1 - currentValue);

 45:                 return point;

 46:             }

 47:             else

 48:                 return null;

 49:         }

 50: 

 51:         public object ConvertBack(object value, Type targetType,

 52:             object parameter, CultureInfo cultureInfo)

 53:         {

 54:             throw new NotImplementedException();

 55:         }

 56:     }

 57: }

 58: 
This is the output of the program.

If we change the slider position then starting and ending position of linear gradient also changes.