添加代码时ComboBox无法打开

Question

我正在尝试将代码中的ComboBox添加到WPF UserControl中。 ComboBox按预期添加并显示我在ComboBox中设置的默认值，但是当我按下它时，它不会打开。

这是试图绑定数据的代码，只是其中的一部分：

public class SelectRecentData : INotifyPropertyChanged
{
    public ObservableCollection<ComboBoxItem> projectItems { get; set; }
    private ComboBoxItem _selectedprojectItem;

    public ComboBoxItem SelectedprojectItem
    {
        get
        {
            return _selectedprojectItem;
        }
        set
        {
            this._selectedprojectItem = value;
            this.onPropertyChanged("SelectedprojectItem");
        }
    }
}

这是生成和插入ComboBox的代码：

SelectRecentData Data = new SelectRecentData();
ComboBox cbo = new ComboBox();
cbo.SetBinding(ComboBox.ItemsSourceProperty,new Binding(){
        bind.Source = Data; //Data is the class mentioned above
        bind.Path = new PropertyPath("projectItems");}
cbo.SetBinding(ComboBox.SelectedItemProperty,new Binding(){
        bind.Source = Data;
        bind.Path = new PropertyPath("SelectedprojectItem");});
cbo.Name = name;
cbo.Margin = new Thickness(0.5,0.5,0.5,0.5);
cbo.Width = 200;
sp.Children.Add(cbo); //sp is the StackPanel

如果您按下页面上的按钮，这是测试添加项目的代码：

var defaultvalue = new ComboBoxItem { Content = "Added "+mycounter };
Data.projectItems.Add(defaultvalue);
Data.SelectedprojectItem = defaultvalue;
mycounter++;