如何使用 MVVM 在 RibbonComboBox 上设置 SelectedItem？

我该如何设置SelectedItem on a RibbonComboBox using MVVM图案？

View

<ribbon:RibbonComboBox>
    <ribbon:RibbonGallery SelectedItem="{Binding Foobar, Mode=TwoWay}">
        <ribbon:RibbonGalleryCategory ItemsSource="{Binding Foobars}" DisplayMemberPath="FoobarID" />
    </ribbon:RibbonGallery>
</ribbon:RibbonComboBox>

视图模型

// Selected Item
private Foobar _foobar { get; set; }

public Foobar Foobar
{
    get { return _foobar; }
    set
    {
        if (value == _foobar || value == null)
            return;

        _foobar = value;

        base.NotifyPropertyChanged("Foobar");
    }
}   

// Collection
private ObservableCollection<Foobar> _foobars = new ObservableCollection<Foobar>();

public ObservableCollection<Foobar> Foobars
{
    get
    {
        return _foobars;
    }
}

// Constructor
public FoobarViewModel(MyObject myObject)
{
    LoadFoobars();

    Foobar = myObject.Foobar;
}

// Method
private void LoadFoobars()
{
    foreach (var foobar in _localRepository.GetFoobars())
    {
        this._foobars.Add(foobar);
    }
}

Update

去除IsEditable="True"确实将“Namespace.Foobar”放入RibbonComboBox和改变SelectedItem并添加SelectedValuePath on the RibbonGallery确实显示了正确的值，但是RibbonComboBox有红色边框，所以我猜它没有经过验证（就像比较苹果和梨一样）。

<ribbon:RibbonComboBox>
    <ribbon:RibbonGallery SelectedItem="{Binding Foobar.FoobarID, Mode=TwoWay}" SelectedValuePath="DisplayMemberPath">
        <ribbon:RibbonGalleryCategory ItemsSource="{Binding Foobars}" DisplayMemberPath="FoobarID"/>
    </ribbon:RibbonGallery>
</ribbon:RibbonComboBox>

我通过更改构造函数解决了这个问题。

// Constructor
public FoobarViewModel(MyObject myObject)
{
    LoadFoobars();

    Foobar = _repository.GetFoobar(myObject.FoobarID);
}