SelectionChanged event binding in Silverlight+MVVM-Light

Question

The handler of the "SelectionChanged" event of the ComboBox control has the following signature:

void SelectionChangedMethod(object sender, SelectionChangedEventArgs e)

How to bind to that property under Silverlight 4 and MVVM-Light to the corresponding method of the ViewModel object?

As far as I know, I need to do something like this:

public void Changed(Object obj, SelectionChangedEventArgs e)
{
    // .... implement logic here
}

RelayCommand<Object, SelectionChangedEventArgs> _command;
public ICommand ObjectSelectionChanged
{
    get
    {
        if (_command == null)
        {
            _command = new RelayCommand<Object, SelectionChangedEventArgs>(Changed);
        }
        return _command;
    }
}

The problem is that RelayCommand class in the MVVM-Light framework doesn't support 2 generic parameters...

Is there any solution or workaround for this case? How bind control event to the method with 2 parameters?

And another problem: ComboBox doesn't have "Command" property to bind this command..? How can I get event to the ViewModel?

Thanks.

P.S. I've tried to use SelectedItem property of the combobox, but it seems like ComboBox implementation is not correct and it doesn't work...

Agies Agies · Accepted Answer · 2010-05-29T03:28:46

There is a much easier approach then trying to connect the SelectedChangedEvent.

Try...

<ComboBox ItemsSource={Binding Path=Names} SelectedItem={Binding Path=SelectedName, Mode=TwoWay}>

public class ViewModel : ViewModelBase
{
    private string _selectedName;
    public string SelectedName
    {
        get { return _selectedName; }
        set
        {
            if (_selectedName == value) return;
            _selectedName = value;
            RaisePropertyChanged("SelectedName");
        }
    }
}

It is possible to do it the way you were going

<GalaSoft_MvvmLight_Command:EventToCommand Command="{Binding MyCommand}" PassEventArgsToCommand="True"/>

The Command should be a RelayCommand of type 'SelectionChangedEventArgs'

SelectionChanged event binding in Silverlight+MVVM-Light

1 Answers