ribbon combo box selection changed event not firing

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C#

WPF

combobox

I have a combobox in a ribbon bar as follows:

<r:ribboncombobox xmlns:r="#unknown">
                                Label="Saved Queries" Name="Saved_Queries" ToolTip="Select an item to run or edit" >
                                <r:ribbongallery>
                                    ScrollViewer.VerticalScrollBarVisibility="Auto"  SelectionChanged="RibbonGallery_SelectionChanged" >
                                    
                                    <r:ribbongallery.categorystyle>
                                        <Style TargetType="{x:Type r:RibbonGalleryCategory}" 
                                    BasedOn="{StaticResource {x:Type r:RibbonGalleryCategory}}">
                                            <setter property="MinColumnCount" value="1" />
                                            <setter property="MaxColumnCount" value="1" />
                                            <Style.Triggers>
                                                <trigger property="Header" value="Automatic Brush">
                                                    <setter property="HeaderVisibility" value="Collapsed" />
                                                    <setter property="MinColumnCount" value="1" />
                                                    <setter property="MaxColumnCount" value="1" />
                                                    <setter property="IsSharedColumnSizeScope" value="True" />
                                                </trigger>
                                            </Style.Triggers>
                                        </Style>
                                    </r:ribbongallery.categorystyle>
                                    <r:ribbongallery.galleryitemtemplate>
                                        <datatemplate>
                                            <grid>
                                                
                                            </grid>
                                        </datatemplate>
                                    </r:ribbongallery.galleryitemtemplate>
                                    <r:ribbongallerycategory>
                                    </r:ribbongallerycategory>
                                </r:ribbongallery>
                            </r:ribboncombobox>

When an item is selected in the combobox, im opening a new window.I am populating the combobox with an xml. But this does not happen. how can i go about this?