如何在xamarin窗体的工具栏中添加选择器

<ContentPage.ToolbarItems>
    <ToolbarItem>
        <ToolbarItem.Icon>
            <OnPlatform x:TypeArguments="FileImageSource">
                <On Platform="iOS" Value="icon.png" />
                <On Platform="Android" Value="icon.png" />
            </OnPlatform>
        </ToolbarItem.Icon>
        <ToolbarItem.Order>Primary</ToolbarItem.Order>
        <ToolbarItem.Priority>0</ToolbarItem.Priority>
        <ToolbarItem.Activation>
            <OnPlatform x:TypeArguments="Command">
                <On Platform="iOS, Android" Value="{Binding ToolbarItemCommand}" />
            </OnPlatform>
        </ToolbarItem.Activation>
        <ToolbarItem.Text>
            <OnPlatform x:TypeArguments="x:String">
                <On Platform="iOS" Value="Select" />
                <On Platform="Android" Value="Select" />
            </OnPlatform>
        </ToolbarItem.Text>
    </ToolbarItem>
</ContentPage.ToolbarItems>

public partial class MainPage : ContentPage
{
    public ICommand ToolbarItemCommand { get; private set; }

    public MainPage()
    {
        InitializeComponent();

        ToolbarItemCommand = new Command(OnToolbarItemSelected);
    }

    private void OnToolbarItemSelected()
    {
        // 处理选择器的选项
        var selectedOption = picker.SelectedItem.ToString();
        // 执行相应的操作
    }
}