wpf下拉框不能多选的原因

<dxe:ComboBoxEdit Margin="0"  Height="25" Width="65" VerticalAlignment="Center" Grid.Column="3"
                       IsTextEditable="False"
                         EditValue="{Binding SelectCityList, Mode=TwoWay}"
                         SelectedIndex="0"
                        ItemsSource="{Binding CityList}"
                        DisplayMember="Name">
                        <dxe:ComboBoxEdit.StyleSettings>
                            <dxe:CheckedComboBoxStyleSettings />
                        </dxe:ComboBoxEdit.StyleSettings>
                    </dxe:ComboBoxEdit>

红色部分必须要写对，如果EditValue  写成了 SelectedItem那么就会出错！