WPF组合框未显示SQL

Question

请有人告诉我为什么我的组合框没有填充？

请注意以下事项： _memberReference从另一个表单传递。 为了简洁，省略了另一个组合框。 枚举正确填充下拉框。 这是来自SQL表的数据没有显示在组合框中。我缺少什么？

<Window.Resources>
<ObjectDataProvider x:Key="pa_enum"
                MethodName="GetValues"
                ObjectType="{x:Type core:Enum}">
    <ObjectDataProvider.MethodParameters>
        <x:Type Type="local2:PossibleAnswerEnum"/>
    </ObjectDataProvider.MethodParameters>
</ObjectDataProvider>

<ComboBox x:Name="cmbQ1"
  FontSize="16"
  Margin="5"
  Grid.Row="0" 
  Grid.Column="4"
  Grid.ColumnSpan="1"
  ItemsSource="{Binding Source={StaticResource pa_enum}}" 
  SelectedValue="{Binding Q1}"> 

public partial class ExtractionForm : Window
{
public string Type;
public string SelectedMemberReference;
public string ts;
public ExtractionForm(string _memberReference)
{

InitializeComponent();
var obj = DataRepository.GetMemberDetails(_memberReference);
DGMemberDetails.ItemsSource = obj;
SelectedMemberReference = _memberReference;

var RecordsUpdated = DataRepository.GetMember(SelectedMemberReference);
DataContext = RecordsUpdated;

ts = UserInfo.GetTimeStamp();
}
}

    public static ObservableCollection<ExtractedData> GetMember (string memberid)
{
var DataObj = new ObservableCollection<ExtractedData>();

var dt = StoredProcedure.GetMemberData("dbo.ExtractedData", memberid);

foreach (DataRow dr in dt.Rows)
{
    DataObj.Add(new ExtractedData()
    {
        MemberReference = dr["MemberReference"].ToString(),
        Q1 = dr["Question1"].ToString(),
        Q2 = dr["Question2"].ToString()
    });
}

return DataObj;
}


public class ExtractedData: INotifyPropertyChanged
{
private string memberReference;
private string q1;
private string q2;
private PossibleAnswerEnum possibleanswer;

public string MemberReference
{
    get { return memberReference; }
    set
    {
        memberReference = value;
        RaisePropertyChanged(); ;
    }
}

public string Q1
{
    get { return q1; }
    set
    {
        q1 = value;
        RaisePropertyChanged(); ;
    }
}

public string Q2
{
    get { return q2; }
    set
    {
        q2 = value;
        RaisePropertyChanged(); ;
    }
}

public PossibleAnswerEnum PossibleAnswer
{
    get
    {
        return possibleanswer;
    }
    set
    {
        possibleanswer = value;
        RaisePropertyChanged();
    }
}

public event PropertyChangedEventHandler PropertyChanged;
private void RaisePropertyChanged(
    [CallerMemberName] string caller = "")
{
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(caller));
}
}

public enum PossibleAnswerEnum
{
Yes,
No,
Unclear
}