我设法让它工作
我将所有用于设置 selectedValue 的代码移到了 DropDownList 的 DataBound 事件中。在这种情况下，数据绑定已经发生，值列表可供我设置 selectedValue。我不再自己调用 DataBind，因为无论如何它都在控件上被调用。我只在开头添加“进行选择”项并将 AppendDataBoundItems 设置为 true。
现在在某些只读状态下可能存在未处理的情况，因为我不处理任何 Cell.Databinding() 事件。
完整的源代码供有兴趣的人...
它基于CodeProjct上 Javad Zarrinabadi 的示例
用法：
DropDownBoundField dropDownBoundField = new DropDownBoundField();
dropDownBoundField.HeaderText = "NyColumnName";
dropDownBoundField.BusinessObjectName = "BusinessLogic.MyDataClass";
dropDownBoundField.SelectMethod = "GetEnumerable";
dropDownBoundField.DataTextField = "Name"; // what should be displayed
dropDownBoundField.DataValueField = "Id"; // value behind the displayed text
dropDownBoundField.DataField = "IdProperty"; // Property to bind to
dropDownBoundField.DefaultValueText = "Select"; // text on first item as
default if DataField is null
dropDownBoundField.FindBy = SetSelectedValueBy.Value // Choose how the DataField is being evaluated, as source for the value or the text
GridView.Columns.Add(dropDownBoundField);
班级：
using System;
using System.Web.UI.WebControls;
using System.Web.UI;
using System.ComponentModel;
using System.Web;
using System.Collections.Specialized;
namespace IDVCode.GridViews
{
public class DropDownField : BoundField
{
#region fields
private string _listDataSourceID;
private string _listDataMember;
private string _listDataTextField;
private string _listDataValueField;
#endregion
#region eventHandler
protected override void InitializeDataCell(DataControlFieldCell cell, DataControlRowState rowState)
{
DropDownList dropDownList = new DropDownList();
dropDownList.ToolTip = HeaderText;
dropDownList.DataSourceID = ListDataSourceID;
dropDownList.DataMember = ListDataMember;
dropDownList.DataTextField = ListDataTextField;
dropDownList.DataValueField = ListDataValueField;
dropDownList.Enabled = !ReadOnly;
cell.Controls.Add(dropDownList);
if (rowState == DataControlRowState.Normal || rowState == DataControlRowState.Alternate || ReadOnly)
{
dropDownList.Enabled = false;
}
if (DataField.Length != 0) // && ((rowState & DataControlRowState.Edit) != DataControlRowState.Normal))
{
dropDownList.DataBound += new EventHandler(OnDataBindField);
}
}
protected override void OnDataBindField(object sender, EventArgs e)
{
Control control = (Control)sender;
Control namingContainer = control.NamingContainer;
object dataValue = GetValue(namingContainer);
bool encode = (SupportsHtmlEncode && HtmlEncode) && (control is TableCell);
string str = FormatDataValue(dataValue, encode);
if (control is TableCell)
{
if (str.Length == 0)
{
str = " ";
}
((TableCell)control).Text = str;
}
else
{
if (!(control is DropDownList))
{
throw new HttpException("BoundField_WrongControlType");
}
if (((DropDownList)control).Items.Count > 0) // Don't call selectedValue if empty
{
if (dataValue != null)
{
DropDownList dropDownList = (DropDownList)control;
ListItem item = null;
if (FindBy == SetSelectedValueBy.Value)
{
item = dropDownList.Items.FindByValue(dataValue.ToString());
}
else
{
item = dropDownList.Items.FindByText(dataValue.ToString());
}
if (item != null)
dropDownList.Text = item.Value;
else
{
ListItem defaultItem = dropDownList.Items.FindByText(DefaultValueText);
if (defaultItem != null)
dropDownList.SelectedValue = defaultItem.Value;
}
}
}
}
}
public override void ExtractValuesFromCell(IOrderedDictionary dictionary, DataControlFieldCell cell,
DataControlRowState rowState, bool includeReadOnly)
{
Control control = null;
string dataField = DataField;
object text = null;
string nullDisplayText = NullDisplayText;
if (((rowState & DataControlRowState.Insert) == DataControlRowState.Normal) || InsertVisible)
{
if (cell.Controls.Count > 0)
{
control = cell.Controls[0];
DropDownList box = control as DropDownList;
if (box != null)
{
text = box.SelectedValue;
}
}
else if (includeReadOnly)
{
string s = cell.Text;
if (s == " ")
{
text = string.Empty;
}
else if (SupportsHtmlEncode && HtmlEncode)
{
text = HttpUtility.HtmlDecode(s);
}
else
{
text = s;
}
}
if (text != null)
{
if (((text is string) && (((string)text).Length == 0)) && ConvertEmptyStringToNull)
{
text = null;
}
if (((text is string) && (((string)text) == nullDisplayText)) && (nullDisplayText.Length > 0))
{
text = null;
}
if (dictionary.Contains(dataField))
{
dictionary[dataField] = text;
}
else
{
dictionary.Add(dataField, text);
}
}
}
}
#endregion
#region Properties
public virtual string ListDataSourceID
{
get
{
if (_listDataSourceID == null)
{
object stateBag = ViewState["ListDataSourceID"];
if (stateBag != null)
{
_listDataSourceID = (string)stateBag;
}
else
{
_listDataSourceID = string.Empty;
}
}
return _listDataSourceID;
}
set
{
if (!object.Equals(value, ViewState["ListDataSourceID"]))
{
ViewState["ListDataSourceID"] = value;
_listDataSourceID = value;
OnFieldChanged();
}
}
}
public virtual string ListDataMember
{
get
{
if (_listDataMember == null)
{
object stateBag = ViewState["ListDataMember"];
if (stateBag != null)
{
_listDataMember = (string)stateBag;
}
else
{
_listDataMember = string.Empty;
}
}
return _listDataMember;
}
set
{
if (!object.Equals(value, ViewState["ListDataMember"]))
{
ViewState["ListDataMember"] = value;
_listDataMember = value;
OnFieldChanged();
}
}
}
public virtual string ListDataTextField
{
get
{
if (_listDataTextField == null)
{
object stateBag = ViewState["ListDataTextField"];
if (stateBag != null)
{
_listDataTextField = (string)stateBag;
}
else
{
_listDataTextField = string.Empty;
}
}
return _listDataTextField;
}
set
{
if (!object.Equals(value, ViewState["ListDataTextField"]))
{
ViewState["ListDataTextField"] = value;
_listDataTextField = value;
OnFieldChanged();
}
}
}
public virtual string ListDataValueField
{
get
{
if (_listDataValueField == null)
{
object stateBag = ViewState["ListDataValueField"];
if (stateBag != null)
{
_listDataValueField = (string)stateBag;
}
else
{
_listDataValueField = string.Empty;
}
}
return _listDataValueField;
}
set
{
if (!object.Equals(value, ViewState["ListDataValueField"]))
{
ViewState["ListDataValueField"] = value;
_listDataValueField = value;
OnFieldChanged();
}
}
}
[Description("Sets a default value if applicable")]
[Category("Appearance")]
public string DefaultValueText
{
get
{
object val = ViewState["DefaultValueText"];
if (val != null)
{
return (string)val;
}
return (string.Empty);
}
set
{
ViewState["DefaultValueText"] = value;
}
}
[Description("Defines how the SelectedValue is set")]
[Category("Data")]
[DefaultValue(SetSelectedValueBy.Value)]
public SetSelectedValueBy FindBy
{
get
{
object val = ViewState["SetSelectedValueBy"];
return val != null ? (SetSelectedValueBy) val : SetSelectedValueBy.Value;
}
set
{
ViewState["SetSelectedValueBy"] = value;
}
}
public enum SetSelectedValueBy
{
Text,
Value
}
#endregion
}
}