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

I know this thread is old, but I've faced the same problem yesterday where everything was written correctly yet the WPF was still refusing to locate the converter. What helped me was assigning the converter in the following manner:

<MultiBinding Converter="{local:ButtonParametersMultiValueConverter}">

That solved the issue.