视图有一个组合框，其中ObservableCollection<Vendor>作为源，SelectedItem绑定到ViewModel中定义的Contact。尽管在ViewModel的构造函数中成功地为Contact赋值，但在加载视图时没有显示任何内容。
视图

<ComboBox Grid.Row="0" Grid.Column="2"
          ItemsSource="{Binding Vendors}"
          SelectedItem="{Binding Contact.Vendor, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
          DisplayMemberPath="Id" SelectedValuePath="Key"
          IsSynchronizedWithCurrentItem="True"
          IsEditable="True" />

视图模型

private ObservableCollection<Vendor> vendors;
public ObservableCollection<Vendor> Vendors
{
    get
    {
        if(vendors == null)
        {
            vendors = new ObservableCollection<Vendor>(_contactsRepository.GetVendors());
        }
        return vendors;
    }
    set
    {
        if (vendors == value) return;

        vendors = value;
        OnPropertyChanged();
    }
}

private Contact contact;
public Contact Contact
{
    get
    {
        if(contact == null)
        {
            contact = new Contact();
        }
        return contact;
    }
    set
    {
        if (contact == value) return;

        contact = value;
        OnPropertyChanged();
    }
}

public ModContactViewModel(ContactsRepository contactsRepository, bool isEditing, Contact contact)
{
    _contactsRepository = contactsRepository;
    IsEditing = isEditing;
    Contact = contact;
}

接触模型

public class Contact : ObservableObject
{
    private Vendor vendor;
    public Vendor Vendor
    {
        get
        {
            return vendor;
        }
        set
        {
            if (vendor == value) return;

            vendor = value;
            OnPropertyChanged();
        }
    }

    private string contactId;
    public string ContactId
    {
        get
        {
            return contactId;
        }
        set
        {
            if (contactId == value) return;

            contactId = value;
            OnPropertyChanged();
        }
    }

    private string contactEmail;
    public string ContactEmail
    {
        get
        {
            return contactEmail;
        }
        set
        {
            if (contactEmail == value) return;

            contactEmail = value;
            OnPropertyChanged();
        }
    }

    private string comments;
    public string Comments
    {
        get
        {
            return comments;
        }
        set
        {
            if (comments == value) return;

            comments = value;
            OnPropertyChanged();
        }
    }
}

供应商模型

public class Vendor : ObservableObject
{
    private int key;
    public int Key
    {
        get
        {
            return key;
        }
        set
        {
            if (key == value) return;

            key = value;
            OnPropertyChanged();
        }
    }

    private string id;
    public string Id
    {
        get
        {
            return id;
        }
        set
        {
            if (id == value) return;

            id = value;
            OnPropertyChanged();
        }
    }

    private string name;
    public string Name
    {
        get
        {
            return name;
        }
        set
        {
            if (name == value) return;

            name = value;
            OnPropertyChanged();
        }
    }
}