How can I binding the SelectedItems property of a DataGrid in MVVM?

Question

Well, I am using MVVM Light and I have tried the solution to pass as parameter the selectedItems of the datagrid in the event selectionChanged. So I can get the selecteditems and I can update my variable in the view model.

In a first moment, it is a good solution. The problem is that if I set in my view model the SelectedIndex property to -1 to deselect all or set to null the SelectedItem property, the event selectionChanged is not fired. I guess that really is it good, because why the view will notify to the view model the change of a property that is changed in a first moment in the view model? This does not create cycles, but then I need to clear my SelectedItems propery in my view model manually and notifiy and rise my event OnSelectionChanged to another view models changes in many parts of my code.

I would like to know how can I force to rise the selectionChagend event when I change the property in my view model. Perhaps the solution could be a attached property instead of using the event selectionChanged.

Which alternatives do I have?

Thank you.

Answer 1

Use RaisePropertyChanged in the setter of the selected item.

private T _selectedItem;
public T SelectedItem
{
    get
    {
        return _selectedItem;
    }
    set
    {
        if(value != _selectedItem)
        {
            _selectedItem = value;
            RaisePropertyChanged("SelectedItem");
        }
    }
}

Or take a look at this one: INotifyPropertyChanged Is Obsolete and this one: Data Binding without INotifyPropertyChanged

EDIT: Since 4.6 there's a more beautiful way:

private T _selectedItem;
public T SelectedItem
{
    get
    {
        return _selectedItem;
    }
    set
    {
        if(value != _selectedItem)
        {
            _selectedItem = value;
            OnPropertyChanged();
        }
    }
}

protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    => RaisePropertyChanged(propertyName);

CallerMemberName is for passing the Name of the calling member implicitly.