WPF:设置不能输入的下拉选择框--MyLookUpEdit

<Base:MyLookUpEdit x:Name="comboBox_ss_no" Height="24"  VerticalContentAlignment="Center" Grid.Column="1" Grid.Row="3"
                                    DisplayMember="Name"
                                    ValueMember="Code"
                                    AutoPopulateColumns="False"
                                    AutoComplete="False"
                                    IncrementalFiltering="True"
                                    ImmediatePopup="True">
                                    <Base:MyLookUpEdit.ColumnsToFilter>
                                        <Base:ColumnItem FieldName="Name"/>
                                        <Base:ColumnItem FieldName="ZiMu"/>
                                    </Base:MyLookUpEdit.ColumnsToFilter>
                                    <dxg:LookUpEdit.PopupContentTemplate>
                                        <ControlTemplate>
                                            <dxg:GridControl Name="PART_GridControl">
                                                <dxg:GridControl.Columns>
                                                    <dxg:GridColumn FieldName="Name" Header="民族名称"/>
                                                </dxg:GridControl.Columns>
                                                <dxg:GridControl.View>
                                                    <dxg:TableView AutoWidth="True" ShowSearchPanelFindButton="True"/>
                                                </dxg:GridControl.View>
                                            </dxg:GridControl>
                                        </ControlTemplate>
                                    </dxg:LookUpEdit.PopupContentTemplate>
                                </Base:MyLookUpEdit>