Multibinding with RelayCommand returns unset values

Question

I have a command that binds to a menu item I have, I would like to pass more than one parameter. I have tried using a converter however it seems to return nothing.

My converter

public class AddConverter : IMultiValueConverter {
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
        return values.Clone();
    }
    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture) {
        throw new NotImplementedException();
    }
}

My View model containing my command

class myViewModel: ViewModelBase {

private RelayCommand testCommand;

        public ICommand TestCommand {
            get {
                if (testCommand == null) {
                    testCommand = new RelayCommand((param) => test((object[])param));
                }
                return testCommand ;
            }
        }

        //Only trying to print out one of the params as a test
        public void test(object parameter) {
            var values = (object[])parameter;
            int num1 = Convert.ToInt32((string)values[0]);
            MessageBox.Show(num1.ToString());
        }

My binding on my menu item

//Using tags as a test
<ContextMenu>
    <MenuItem Name="testing" Header="Move to Position 10" Command="{Binding TestCommand}" Tag="7">
        <MenuItem.CommandParameter>
             <MultiBinding Converter="{StaticResource AddConverter}">
                 <Binding ElementName="testing" Path="Tag"/>
                 <Binding ElementName="testing" Path="Tag"/>
             </MultiBinding>
        </MenuItem.CommandParameter>
    </MenuItem>
</ContextMenu>

After debugging, when I open my window containing the menu item, the converter fires off, the values object is null at that point. Then, when I select my menu item and fire off the command, when I get to my execution, the parameter is null. I don't understand why my converter fires off before I even click the menu item, or why the values are null.

Answer 1

Try to replace the ElementName of the bindings with a RelativeSource . This works for me:

<MenuItem Name="testing" Header="Move to Position 10" Command="{Binding TestCommand}" Tag="7">
    <MenuItem.CommandParameter>
        <MultiBinding Converter="{StaticResource AddConverter}">
            <Binding Path="Tag" RelativeSource="{RelativeSource Self}"/>
            <Binding Path="Tag" RelativeSource="{RelativeSource Self}"/>
        </MultiBinding>
    </MenuItem.CommandParameter>
</MenuItem>

Also note that you should bind to the T estCommand property and not to the testCommand field.