Question

I’ve faced strange issue with Silverlight DataGrid.
When I’m binding list of structs (placed in ViewModel) to grid values are displayed properly, but for some reason changes that are made to grid are not reflected in ViewModel.

public struct ObjectSelection 
{
    public bool Selected { get; set; }
    public string Name { get; set; }
}

public List<ObjectSelection> SelectedObjects
{
    get { return _selectedObjects; }
    set
    {
        if (value != _selectedObjects)
        {
            _selectedObjects= value;
            FirePropertyChanged("SelectedObjects");
        }
    }
}

XAML:

<navigation:DataGrid AutoGenerateColumns="False" ItemsSource="{Binding SelectedObjects, Mode=TwoWay}"                                    
    <navigation:DataGrid.Columns>
        <navigation:DataGridFilterTemplateColumn Header="Selected"
            CanUserFilter="True"
            CanUserSort="False"
            DataType="Boolean"
            SortMemberPath="Include">
            <navigation:DataGridFilterTemplateColumn.CellTemplate>
                <DataTemplate>
                    <controls:CheckBox HorizontalAlignment="Center"
                        VerticalAlignment="Center"
                        IsChecked="{Binding Selected, Mode=TwoWay}"/>
                </DataTemplate>
            </navigation:DataGridFilterTemplateColumn.CellTemplate>
        </navigation:DataGridFilterTemplateColumn>                                        
        <navigation:DataGridFilterColumn Header="Dimension"
            DataType="String" 
            CanUserFilter="False"
            IsReadOnly="True"
            Binding="{Binding Name}" 
            CanUserSort="True"                                              
            SortMemberPath="Name"
            Width="*"/>
    </navigation:DataGrid.Columns>
</navigation:DataGrid>

Answer 1

You shouldn’t define ObjectSelection as struct.

A struct is copied every time it is read from your property. That copy is used for binding. If that copy is then modified by the user, the original remains unchanged. I suggest you use a class instead of a struct. In almost all cases, classes are the better choice.

Microsofts recommendation:

Consider defining a structure instead of a class if instances of the
type are small and commonly short-lived or are commonly embedded in
other objects.

Do not define a structure unless the type has all of the following
characteristics:

• It logically represents a single value, similar to primitive types (integer, double, and so on).
• It has an instance size smaller than 16 bytes.
• It is immutable.
• It will not have to be boxed frequently.