Multibinding generates “Cannot set MultiBinding because MultiValueConverter must be specified”

Question

I have a button with binding which works fine, see below:

<Button x:Name="licenceFilterSet" Content="Search" Command="{Binding searchCommand}" CommandParameter="{Binding Path=Text, ElementName=licenseTextBox}" />

Now I have realized that I need yet another piece of information, so I need to send the value of a check-box as well. I modified the VM like this:

<Button x:Name="licenceFilterSet" Content="Search" Command="{Binding licenseSearchCommand}">
    <Button.CommandParameter>
        <MultiBinding Converter="{StaticResource searchFilterConverter}">
            <Binding Path="Text" ElementName="licenseTextBox" />
            <Binding Path="IsEnabled" ElementName="regularExpressionCheckBox" />
        </MultiBinding>
    </Button.CommandParameter>
</Button>

Below is my multi-converter:

/// <summary>
/// Converter Used for combining license search textbox and checkbox
/// </summary>
public class SearchFilterConverter : IMultiValueConverter
{
    public object Convert(object[] values)
    {
        return new Tuple<String, bool>((String)values[0], (bool)values[1]);
    }
}

What am I doing wrong. I am getting the following error, (which is pointing to my MultiBinding-tag in XAML):

Cannot set MultiBinding because MultiValueConverter must be specified.

Answer 1

you have to implement IMultiConverter

public class SearchFilterConverter : IMultiValueConverter
{
 public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
 {
    return new Tuple<String, bool>((String)values[0], (bool)values[1]);;
 }
 public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

then create the resource in xaml

 <Converter:SearchFilterConverter x:Key="searchFilterConverter" />

then it should work

<Button x:Name="licenceFilterSet" Content="Search" Command="{Binding licenseSearchCommand}">
<Button.CommandParameter>
    <MultiBinding Converter="{StaticResource searchFilterConverter}">
        <Binding Path="Text" ElementName="licenseTextBox" />
        <Binding Path="IsEnabled" ElementName="regularExpressionCheckBox" />
    </MultiBinding>
</Button.CommandParameter>
</Button>

Answer 2

That is not the correct implementation of the IMultiValueConverter interface.

The correct one is:

public class SearchFilterConverter : IMultiValueConverter
{
   public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
   {
      ....
   }

   public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
   {
   }
}

Reference here.