AddHandler 到 FrameworkElementFactory ComboBox - 类型错误？

如何解决AddHandler 到 FrameworkElementFactory ComboBox - 类型错误？

已经阅读了许多关于这个明显令人烦恼的问题的答案，包括这个似乎指明了方向的出色回复：Add handler to factory，经过几天的尝试，我仍然无法在我的设置中使用它在本网站上阅读了各种不同的建议。

底层数据结构的公共成员是这样的：

    #region Public Members
    public EMSBasicDevice Device    { get => _Device;           set => _Device = value; }
    public BitmapImage DeviceIcon   { get => _DeviceIcon;       set => _DeviceIcon = value; }
    public string DeviceIconPath    { get => _DeviceIconPath;   set => _DeviceIconPath = value; }
    public int RowHeight            { get => _RowHeight;        set => _RowHeight = value; }
    public Color RowColour          { get => _RowColour;        set => _RowColour = value; }
    public string DataDescription   { get => _DataDescription;  set => _DataDescription = value; }
    public string ZoneText          { get => _Zone;             set => _Zone = value; }
    public string LocationText      { get => _LocationText;     set => _LocationText = value; }
    public bool IsHeader            { get => _IsHeader;         set => _IsHeader = value; }
    public InputOutput IOType       { get => _IOType;           set => _IOType = value; }
    public CellControl ShowCombo    { get => _ShowCombo;        set => _ShowCombo = value; }
    public int IOPoint              { get => _IOPoint;          set => _IOPoint = value; }
    public int IOIndex              { get => _IOIndex;          set => _IOIndex = value; }
    public int RowNumber            { get => _RowNumber;        set => _RowNumber = value; }
    public Visibility SensorVis     { get => _SensorVis;        set => _SensorVis = value; }
    public IEnumerable ItemsSource  { get => _ItemsSource;      set => _ItemsSource = value; }
    public object SelectedItem      { get => _SelectedItem;     set => _SelectedItem = value; }

    public SelectionChangedEventHandler OnChange;
    #endregion

目标 UI 元素是 DataGrid。所有列都在代码中显式创建。这是用于保存 ComboBox 的第 4 列的代码。为选项列表 (ItemsSource)、选定项、是否显示控件（不是在网格的每一行上）和（尝试）传递对“更改处理程序”的引用提供绑定。工厂元素 ComboBox 没有用于更改处理程序的 DP。所以我的代码看起来像这样，按照上面链接中给出的信息：

        // Fourth Column: Sensor Settings
        DataGridTemplateColumn SensorSettingCol = new DataGridTemplateColumn();
           
        Binding SensorChoicesBind = new Binding("ItemsSource")
        {
            Mode = BindingMode.TwoWay,UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged,};
        Binding SensorSettingBind = new Binding("SelectedItem")
        {
            Mode                  = BindingMode.TwoWay,UpdateSourceTrigger   = UpdateSourceTrigger.PropertyChanged,NotifyOnSourceUpdated = true
        };
        Binding SensorVisibility = new Binding("SensorVis")
        {
            Mode = BindingMode.TwoWay,UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
        };
        Binding OnChangeBinding = new Binding("OnChange")
        {
            Mode = BindingMode.TwoWay,UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged
        };
        FrameworkElementFactory cbInstance1 = new FrameworkElementFactory(typeof(ComboBox));
        ImageTemplate = new DataTemplate();
        SensorSettingCol.CellTemplate = ImageTemplate;
        SensorSettingCol.Width        = new DataGridLength(150);
        SensorSettingCol.CanUserSort  = false;
        ImageTemplate.VisualTree = cbInstance1;

        cbInstance1.SetBinding(ComboBox.ItemsSourceProperty,SensorChoicesBind);
        cbInstance1.SetBinding(ComboBox.SelectedValueProperty,SensorSettingBind);
        cbInstance1.SetBinding(ComboBox.VisibilityProperty,SensorVisibility);
        
        cbInstance1.AddHandler(ComboBox.SelectionChangedEvent,new RoutedPropertyChangedEventHandler<object>(SelectionChanged));

        TheDataGrid.Columns.Add(SensorSettingCol);


The handler looks like this:

        public void SelectionChanged(object sender,RoutedPropertyChangedEventArgs<object> e)
        {
            //do stuff with e.OriginalSource
        }


Of course,this is only half the problem - the real issue is accessing the actual handler in the dataset
which should be called when the user selects a different choice in the ComboBox. Note that the
implementation is intended to be as generic as possible - the combo Boxes on different rows access
different choices based upon the underlying dataset.

The error message is:

        System.ArgumentException
          HResult=0x80070057
          Message=Handler type is not valid.
          Source=PresentationFramework
          StackTrace:
           at System.Windows.FrameworkElementFactory.AddHandler(RoutedEvent routedEvent,Delegate handler,Boolean handledEventsToo)
           at System.Windows.FrameworkElementFactory.AddHandler(RoutedEvent routedEvent,Delegate handler)
           at EMS_Config_Tool.uicomponents.WPF.DeviceEditControl.SetupDeviceGrid(DataGrid TheDataGrid) in C:\Workspace\90504_SmartCellConfigTool\Trunk\EMS Config Tool\uicomponents\WPF\DeviceEditControl.xaml.cs:line 794

The question is: The handler type is wrong,so what should the type actually be? 
And for a Gold Star,is there a MUCH BETTER way to link the SelectionChanged event 
to the appropriate handler?