WP8中ListBox的SelectionChanged事件绑定Command有关问题，

WP8中ListBox的SelectionChanged事件绑定Command问题，求助，在线等
我在WP8中使用MVVMLight框架 4.1.27.22645

在一个ListBox的SelectionChanged事件中绑定一个Command，在ViewModel中没有触发，在线求助。

XAML代码：

<ListBox x:Name="lstProvinces"
                         ItemTemplate="{StaticResource dtItemTemplate}"
                         ItemsSource="{Binding Provinces}">
                    <ListBox.ItemsPanel>
                        <ItemsPanelTemplate>
                            <toolkit:WrapPanel />
                        </ItemsPanelTemplate>
                    </ListBox.ItemsPanel>
                    <i:Interaction.Triggers>
                        <i:EventTrigger EventName="SelectionChanged">
                            <cmd:EventToCommand Command="{Binding ProvinceSelectedChangedCommand, Mode=OneWay}" CommandParameter="{Binding SelectedItem, ElementName=lstProvinces}" />
                            <!--  CommandParameter="{Binding SelectedItem, ElementName=lstProvinces}"  -->
                            <!--  <i:InvokeCommandAction Command="{Binding ProvinceSelectedChangedCommand}" CommandParameter="ddd" />  -->
                        </i:EventTrigger>
                    </i:Interaction.Triggers>
                </ListBox>

ViewModel中的代码

        private RelayCommand<ProvinceModel> provinceSelectedChangedCommand;

        /// <summary>
        /// Gets the ProvinceSelectedChangedCommand.
        /// </summary>
        public RelayCommand<ProvinceModel> ProvinceSelectedChangedCommand
        {
            get
            {
                return provinceSelectedChangedCommand
                    ?? (provinceSelectedChangedCommand = new RelayCommand<ProvinceModel>(
                                          (province) =>
                                          {
                                              SelectedProvince = province;

                                              //获取当前省份下的城市信息
                                              if (province != null)
                                              {