c＃中的WPF ComboBox - 动态创建可编辑属性

Question

VS中使用c＃的WPF应用程序。我继承ComboBox，将其命名为AutoCompleteComboBox。我需要IsEditable True，做到了。当我在AutoCompleteComboBox（Control）中写入时，每个字符都被添加到字符串的末尾。我无法通过开始键入来删除突出显示，并且我的光标始终位于第一个索引处。 （简而言之，我需要帮助来动态创建＆＃34;可编辑＆＃34;属性）

class AutoCompleteComboBox : ComboBox
{
    /// <summary>
    /// The value of selected items, this is used since what is shown in the TextBox 
    /// can be different than what is to be stored in the database.
    /// </summary>
    public string Value;

    /// <summary>
    /// The original data context of the Dropdown. 
    /// </summary>
    private object _originalDataContext;

    public AutoCompleteComboBox() : base()
    {
        this.IsEditable = true;
        this.StaysOpenOnEdit = true;
        this.IsTextSearchEnabled = false;

        this.KeyDown += filterItems;        
    }

    private void filterItems(object sender, KeyEventArgs e)
    {
        if (this.Text.Length > 0)
        {
            this.IsDropDownOpen = true;
        }

        if (_originalDataContext == null)
        {
            _originalDataContext = this.DataContext;
        }
        // Need to implement exception handling.
        AutoCompleteComboBox cb = (AutoCompleteComboBox)sender;
        string filterCriteria = cb.Text.ToUpper();

        // Whatever the display member path is, that is our search criteria.
        string displayMemberPath = cb.DisplayMemberPath;

        // Datatable with the original goods.
        DataTable table = (DataTable)_originalDataContext;
        try
        {
            // Remove any null entries from the table
            DataTable tableWithoutNulls = table.AsEnumerable()
                .Where(i => i.Field<String>(displayMemberPath) != null).CopyToDataTable();

            // Get the entries that match what the user typed in
            DataTable revisedTable = tableWithoutNulls.AsEnumerable()
                .Where(i => i.Field<String>(displayMemberPath).ToUpper().Contains(filterCriteria)).CopyToDataTable();

            // Set the data context of the control to the new results
            this.DataContext = revisedTable;
        }
        catch (InvalidOperationException)
        {
            // No matches were found. Set the datacontext to blank.
            this.DataContext = new DataTable();
        }
        catch (ArgumentNullException)
        {
            // No matches were found. Set the datacontext to blank.
            this.DataContext = new DataTable();
        }

    }
}