Mvvm-Light Silverlight, using EventToCommand with a Combobox

Question

I've hooked up a ComboBox's SelectedItemChangeEvent to a ICommand in my view model. Everything seems to be working fine however I do not know how to get the SelectedItem of the ComboxBox. I think I need to use the CommandParameter of the EventToCommand - do I bind this to something in my ViewModel that has the selectedItem of the ComboBox? I've tried this:

<ComboBox 
                                      Width="422"
                                      Height="24"
                                      DisplayMemberPath="Name"
                                      ItemsSource="{Binding CategoryTypes}"
                                      SelectedItem="{Binding SelectedCategory}"
                                      >
                                        <i:Interaction.Triggers>
                                            <i:EventTrigger EventName="SelectionChanged">
                                                <MvvmLight:EventToCommand 
                                                  Command="{Binding SelectCategoryCommand,Mode=TwoWay}"
                                                  CommandParameter="{Binding SelectedCategory, Mode=TwoWay}"
                                                  MustToggleIsEnabledValue="True" />
                                            </i:EventTrigger>
                                        </i:Interaction.Triggers>
                                    </ComboBox>

and in my view model:

public ICommand SelectCategoryCommand
        {
            get
            {
                return new SelectCategoryCommand(this);
            }
        }

        public CategoryType SelectedCategory
        {
            get; set;
        }

and the ICommand

public class SelectCategoryCommand : ICommand
    {
        private RowViewModel _rowViewModel;

        public SelectCategoryCommand(RowViewModel rowViewModel)
        {
            _rowViewModel = rowViewModel;
        }

        public bool CanExecute(object parameter)
        {
            return true;
        }

        public event EventHandler CanExecuteChanged;

        public void Execute(object parameter)
        {
            CategoryType categoryType = (CategoryType) parameter;
        }

    }

However the Parameter in the Execute method of the ICommand is always null. I'm stil quite inexperienced with SilverLight so I think I'm really missing something obvious here. Can anyone help? Thanks in advance!

Answer 1

After doing some digging I found that it is very simple to pass the actual SelectionChangedEventArgs as ICommand's execute parameter:

Just set PassEventArgsToCommand="True"

<ComboBox 
                                      Width="422"
                                      Height="24"
                                      DisplayMemberPath="Name"
                                      ItemsSource="{Binding CategoryTypes}"
                                      SelectedItem="{Binding SelectedCategory}"
                                      >
                                        <i:Interaction.Triggers>
                                            <i:EventTrigger EventName="SelectionChanged">
                                                <MvvmLight:EventToCommand 
                                                  Command="{Binding SelectCategoryCommand,Mode=TwoWay}"
                                                  MustToggleIsEnabledValue="True" 
                                                  PassEventArgsToCommand="True"/>
                                            </i:EventTrigger>
                                        </i:Interaction.Triggers>
                                    </ComboBox>

And then in the Execute method do something like:

public void Execute(object parameter)
    {
        SelectionChangedEventArgs e = (SelectionChangedEventArgs)parameter;
        CategoryType categoryType = (CategoryType)e.AddedItems[0];
    }