wpf datagridcheckboxcolumn: how to enable/disable checkboxes

Question

I have a DataGrid with DataGridCheckBoxColumn. The grid has a binding with a list of objects. I want that, if there are N checkboxes checked, the unchecked become disabled, but I don't know how to perform the disable.

<DataGridCheckBoxColumn
    x:Name="IsFixedByBracketColumn"
    Header="Fissato con staffa"
    Binding="{Binding isFixedByBracket, UpdateSourceTrigger=PropertyChanged}"
    IsReadOnly="False">
    <DataGridCheckBoxColumn.ElementStyle>
        <Style TargetType="CheckBox">
            <Style.Triggers>
                <MultiDataTrigger>
                    <MultiDataTrigger.Conditions>
                        <Condition
                            Binding="{Binding
                                HasMaxNumberReached,
                                RelativeSource={RelativeSource AncestorType={x:Type Window}}}"
                            Value="true"/>
                        <Condition
                            Binding="{Binding
                                IsChecked,
                                RelativeSource={RelativeSource Self}}"
                            Value="false"/>
                    </MultiDataTrigger.Conditions>
                    <Setter Property="IsEnabled" Value="False"/>
                </MultiDataTrigger>
            </Style.Triggers>
            <EventSetter
                Event="CheckBox.Checked"
                Handler="DataGridCheckBoxColumn_Checked" />
        </Style>
    </DataGridCheckBoxColumn.ElementStyle>                                        
</DataGridCheckBoxColumn>

Code for the event:

private void DataGridCheckBoxColumn_Checked(object sender, RoutedEventArgs e)
{
    CheckBox cb = (CheckBox)sender;
    if (cb.IsChecked == true)
    {
        this.numberOfCheckboxesChecked++;
    }
    else
    {
        this.numberOfCheckboxesChecked--;
    }

    if (this.numberOfCheckboxesChecked >= maxNumOfPointsPerSide)
    {               
        this.HasMaxNumberReached = true;
    }
    else 
    {
        this.HasMaxNumberReached = false; 
    }              
}

public bool HasMaxNumberReached
{
    get {
        return hasMaxNumberReached;
    }
    set { 
        hasMaxNumberReached = value; 
        RaisePropertyChanged("HasMaxNumberReached");
    }
}

Answer 1

Thanks to Magnus in MSDN Forum, here is the correct answer of the problem:

<DataGrid x:Name="grid" AutoGenerateColumns="False">
        <DataGrid.Resources>
            <Style TargetType="CheckBox" x:Key="style">
                <Style.Triggers>
                    <MultiDataTrigger>
                        <MultiDataTrigger.Conditions>
                            <Condition Binding="{Binding HasMaxNumberReached, RelativeSource={RelativeSource AncestorType={x:Type Window}}}" Value="true"/>
                            <Condition Binding="{Binding IsChecked, RelativeSource={RelativeSource Self}}" Value="false"/>
                        </MultiDataTrigger.Conditions>
                        <Setter Property="IsEnabled" Value="False"/>
                    </MultiDataTrigger>
                </Style.Triggers>
                <EventSetter Event="CheckBox.Checked" Handler="DataGridCheckBoxColumn_Checked" />
                <EventSetter Event="CheckBox.Unchecked" Handler="DataGridCheckBoxColumn_Checked" />
            </Style>
        </DataGrid.Resources>
        <DataGrid.Columns>
        <DataGridCheckBoxColumn x:Name="IsFixedByBracketColumn"  Header="Fissato con staffa" 
                                Binding="{Binding isFixedByBracket, UpdateSourceTrigger=PropertyChanged}" IsReadOnly="False"
                                ElementStyle="{StaticResource style}" EditingElementStyle="{StaticResource style}">

        </DataGridCheckBoxColumn>
        </DataGrid.Columns>
    </DataGrid> 

Here the complete topic