对于 1.1 版本的 asp.net，带有的下拉列表？

Question

在 asp.net 1.1 版本中，是否可以使用 asp:DropDownList 创建一个包含 optgroup 的选择框？

对于较新版本的 ASP.NET 以及涉及 ControlAdapter 或自定义控件（如来自 的解决方案）的解决方案，这里和其他地方也提出了类似的问题SharpPieces 但这一切似乎与 asp.net 1.1 不兼容

这是否是手工制作 html 的唯一方法，或者是否有任何控件能够为这个旧的 asp 渲染带有 optgroup 标记的选择框.net版本？

Answer 1

我前段时间做了一个，当时效果很好。我将发布相关的部分，以便您可以构建自己的部分（我的也有一个只读模式，可以渲染标签，但您可能不需要它）。

    [DefaultProperty("Text"),
        ValidationProperty("SelectedItem"),
        ToolboxData("<{0}:EqualDropDownList runat=server></{0}:EqualDropDownList>"),
        ToolboxBitmap(typeof(EqualDropDownList), "dropdown.BMP")]
    public class EqualDropDownList:DropDownList
    {
/// The field in the datasource which provides values for groups
        /// </summary>
        [DefaultValue(""), Category("Data")]
        public virtual string DataGroupField
        {
            get
            {
                object obj = this.ViewState["DataGroupField"];
                if (obj != null)
                {
                    return (string) obj;
                }
                return string.Empty;
            }
            set
            {
                this.ViewState["DataGroupField"] = value;
            }
        }


        /// <summary>
        /// Render this control to the output parameter specified.
        /// Based on the source code of the original DropDownList method
        /// </summary>
        /// <param name="writer"> The HTML writer to write out to </param>
        protected override void RenderContents(HtmlTextWriter writer)
        {
            ListItemCollection items = this.Items;
            int itemCount = this.Items.Count;
            string curGroup = String.Empty;
            string itemGroup;
            bool bSelected = false;

            if (itemCount <= 0)
            {
                return;
            }

            for (int i = 0; i < itemCount; i++)
            {
                ListItem item = items[i];
                itemGroup = item.Attributes["DataGroupField"];
                if (itemGroup != null && itemGroup != curGroup)
                {
                    if (curGroup != String.Empty)
                    {
                        writer.WriteEndTag("optgroup");
                        writer.WriteLine();
                    }

                    curGroup = itemGroup;
                    writer.WriteBeginTag("optgroup");
                    writer.WriteAttribute("label", curGroup, true);
                    writer.Write('>');
                    writer.WriteLine();
                }

                writer.WriteBeginTag("option");
                if (item.Selected)
                {
                    if (bSelected)
                    {
                        throw new HttpException("Cant_Multiselect_In_DropDownList");
                    }
                    bSelected = true;
                    writer.WriteAttribute("selected", "selected", false);
                }
                foreach (string key in item.Attributes.Keys)
                {
                    writer.WriteAttribute(key, item.Attributes[key], false);
                }                   

                writer.WriteAttribute("value", item.Value, true);
                writer.Write('>');
                HttpUtility.HtmlEncode(item.Text, writer);
                writer.WriteEndTag("option");
                writer.WriteLine();
            }
            if (curGroup != String.Empty)
            {
                writer.WriteEndTag("optgroup");
                writer.WriteLine();
            }
        }


        /// <summary>
        /// Perform data binding logic that is associated with the control
        /// </summary>
        /// <param name="e">An EventArgs object that contains the event data</param>
        protected override void OnDataBinding(EventArgs e)
        {
            // Call base method to bind data
            base.OnDataBinding(e);

            if (this.DataGroupField == String.Empty)
            {
                return;
            }

            // For each Item add the attribute "DataGroupField" with value from the datasource
            IEnumerable dataSource = Util.GetResolvedDataSource(this.DataSource, this.DataMember);
            if (dataSource != null)
            {
                ListItemCollection items = this.Items;
                int i = 0;

                string groupField = this.DataGroupField;
                foreach (object obj in dataSource)
                {
                    string groupFieldValue = DataBinder.GetPropertyValue(obj, groupField, null);
                    ListItem item = items[i];
                    item.Attributes.Add("DataGroupField", groupFieldValue);
                    i++;
                }
            }

        }

}

你也需要这个课程：

public class Util
    {
        /// <summary>
        /// This is copy of the internal ListControl method
        /// </summary>
        /// <param name="dataSource"></param>
        /// <param name="dataMember"></param>
        /// <returns></returns>
        public static IEnumerable GetResolvedDataSource(object dataSource, string dataMember)
        {
            if (dataSource != null)
            {
                IListSource source1 = dataSource as IListSource;
                if (source1 != null)
                {
                    IList list1 = source1.GetList();
                    if (!source1.ContainsListCollection)
                    {
                        return list1;
                    }
                    if ((list1 != null) && (list1 is ITypedList))
                    {
                        ITypedList list2 = (ITypedList) list1;
                        PropertyDescriptorCollection collection1 = list2.GetItemProperties(new PropertyDescriptor[0]);
                        if ((collection1 == null) || (collection1.Count == 0))
                        {
                            throw new HttpException("ListSource_Without_DataMembers");
                        }
                        PropertyDescriptor descriptor1 = null;
                        if ((dataMember == null) || (dataMember.Length == 0))
                        {
                            descriptor1 = collection1[0];
                        }
                        else
                        {
                            descriptor1 = collection1.Find(dataMember, true);
                        }
                        if (descriptor1 != null)
                        {
                            object obj1 = list1[0];
                            object obj2 = descriptor1.GetValue(obj1);
                            if ((obj2 != null) && (obj2 is IEnumerable))
                            {
                                return (IEnumerable) obj2;
                            }
                        }
                        throw new HttpException("ListSource_Missing_DataMember");
                    }
                }
                if (dataSource is IEnumerable)
                {
                    return (IEnumerable) dataSource;
                }
            }
            return null;
        }
    }