WPF CommandParameter MultiBinding 值 null

我只是想将两个控件绑定为命令参数并将它们作为命令传递到我的命令中object[].

XAML:

<UserControl.Resources>
        <C:MultiValueConverter x:Key="MultiParamConverter"></C:MultiValueConverter>
    </UserControl.Resources>

    <StackPanel Orientation="Vertical">
        <StackPanel Orientation="Horizontal">
            <Button Name="Expander" Content="+" Width="25" Margin="4,0,4,0" Command="{Binding ExpanderCommand}">
                <Button.CommandParameter>
                    <MultiBinding Converter="{StaticResource MultiParamConverter}">
                        <Binding ElementName="Content"/>
                        <Binding ElementName="Expander"/>
                    </MultiBinding>
                </Button.CommandParameter>
            </Button>
            <Label FontWeight="Bold">GENERAL INFORMATION</Label>
        </StackPanel>
        <StackPanel Name="Content" Orientation="Vertical" Visibility="Collapsed">
            <Label>Test</Label>
        </StackPanel>
    </StackPanel>

Command:

public ICommand ExpanderCommand
        {
            get
            {
                return new RelayCommand(delegate(object param)
                    {
                        var args = (object[])param;
                        var content = (UIElement)args[0];
                        var button = (Button)args[1];
                        content.Visibility = (content.Visibility == Visibility.Visible) ? Visibility.Collapsed : Visibility.Visible;
                        button.Content = (content.Visibility == Visibility.Visible) ? "-" : "+";
                    });
            }
        }

转换器：

public class MultiValueConverter : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            return values;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException("No two way conversion, one way binding only.");
        }
    }

基本上发生的事情是绑定似乎工作正常并且转换器返回一个object[]包含正确的值，但是当命令执行时，参数是object[]包含相同数量的元素，除了它们null.

有人可以告诉我为什么价值观object[]参数被设置为null?

谢谢， 亚历克斯.

这会做到这一点：

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
    return values.ToArray();
}

看看这个question的解释。