C# WPF Prism区域里的区域无法默认选中？

主页的区域设置后可以默认选中

void CreateMenuBar()
{
    MenuBars.Add(new MenuBar() { Icon = "Home", Title = "首页", NameSpace = "IndexView" });
    MenuBars.Add(new MenuBar() { Icon = "Cog", Title = "设置", NameSpace = "SettingsView" });
}

/// <summary>
/// 配置首页初始化参数
/// </summary>
public void Configure()
{
     regionManager.Regions[PrismManager.MainViewRegionName].RequestNavigate("IndexView");
}

但是进入二级页面后，再设置的区域无法默认选中

public class SettingsViewModel : BindableBase
{
    public SettingsViewModel(IRegionManager regionManager)
    {
        MenuBars = new ObservableCollection<MenuBar>();
        this.regionManager = regionManager;
        NavigateCommand = new DelegateCommand<MenuBar>(Navigate);
        CreateMenuBar();
        //this.regionManager.Regions[PrismManager.SettingsViewRegionName].RequestNavigate("SettingsUserView");
    }

    private void Navigate(MenuBar obj)
    {
        if (obj == null || string.IsNullOrWhiteSpace(obj.NameSpace))
            return;
        regionManager.Regions[PrismManager.SettingsViewRegionName].RequestNavigate(obj.NameSpace);
    }

    public DelegateCommand<MenuBar> NavigateCommand { get; private set; }
    private ObservableCollection<MenuBar> menuBars;
    private readonly IRegionManager regionManager;

    public ObservableCollection<MenuBar> MenuBars
    {
        get { return menuBars; }
        set { menuBars = value; RaisePropertyChanged(); }
    }


    void CreateMenuBar()
    {
        MenuBars.Add(new MenuBar() { Icon = "Cog", Title = "系统设置", NameSpace = "SettingsUserView" });
        MenuBars.Add(new MenuBar() { Icon = "Palette", Title = "个性化", NameSpace = "SkinView" });
        MenuBars.Add(new MenuBar() { Icon = "Information", Title = "关于更多", NameSpace = "AboutView" });
    }

使用this.regionManager.Regions[PrismManager.SettingsViewRegionName].RequestNavigate("SettingsUserView");无法跳转，延迟执行也没用，请问这是什么原因？