dropdownlist.cs

不错的人事管理系统

/*
 *
导读： 
	 1、DropDownList是从ListControl中派生的，
		其派生关系是 object --> Control --> WebControl --> ListControl --> ListBox
		
	 2、ListBox实现了，System.Web.UI.IPostBackDataHandler，
		在其Items的Selected状态改变时，响应SelectedIndexChanged事件
		
	 3、如果AutoPostBack属性值为True，客户端发生Onchange事件时，进行事件的回传，
		具体实现在AddAttributesToRender中
		
	 4、DropDownList只允许单选，ListBox才允许多选！
 * 
 */

using System;

namespace System.Web.UI.WebControls
{
	/// <summary>
	/// Summary description for DropDownList.
	/// </summary>
	public class DropDownList : ListControl, 
		System.Web.UI.IPostBackDataHandler
	{
		public DropDownList()
		{
			//
			// TODO: Add constructor logic here
			//
		}

		protected override void AddAttributesToRender(System.Web.UI.HtmlTextWriter writer) 
		{
			if (this.Page != null)
				this.Page.VerifyRenderingInServerForm(this);
//			writer.AddAttribute(20, this.UniqueID);
			this.AddAttributesToRender(writer);
			if (this.AutoPostBack && this.Page != null) 
			{
//				writer.AddAttribute(22, this.Page.GetPostBackClientEvent(this, ""));
				writer.AddAttribute("language", "javascript");
			}
		}

		protected override ControlCollection CreateControlCollection() 
		{
			return new EmptyControlCollection(this);
		}

		protected override void RenderContents(System.Web.UI.HtmlTextWriter writer) 
		{
			ListItemCollection local0;
			int local1;
			bool local2;
			int local3;
			ListItem local4;

			local0 = this.Items;
			local1 = this.Items.Count;
			local2 = false;
			if (local1 > 0) 
			{
				local3 = 0;
				while (local3 < local1) 
				{
					local4 = local0[local3];
					writer.WriteBeginTag("option");
					if (local4.Selected) 
					{
						if (local2)
							throw new HttpException(System.Web.HttpRuntime.FormatResourceString("Cant_Multiselect_In_DropDownList"));
						local2 = true;
						writer.WriteAttribute("selected", "selected", false);
					}
					writer.WriteAttribute("value", local4.Value, true);
					writer.Write('>');
					System.Web.HttpUtility.HtmlEncode(local4.Text, writer);
					writer.WriteEndTag("option");
					writer.WriteLine();
					local3++;
				}
			}
		}

		
		bool System.Web.UI.IPostBackDataHandler.LoadPostData(string postDataKey, 
			System.Collections.Specialized.NameValueCollection postCollection) 
		{
			string[] local0;
			int local1;

			local0 = postCollection.GetValues(postDataKey);
			if (local0 != null) 
			{
				local1 = this.Items.FindByValueInternal(local0[0]);
				if (this.SelectedIndex != local1) 
				{
					this.SelectedIndex = local1;
					return true;
				}
			}
			return false;
		}

		void System.Web.UI.IPostBackDataHandler.RaisePostDataChangedEvent() 
		{
			this.OnSelectedIndexChanged(System.EventArgs.Empty);
		}

		
		public override int SelectedIndex
		{
			get
			{
				int local0;

				local0 = base.SelectedIndex;
				if((local0 < 0) 
					&& (this.Items.Count > 0)
					)
				{
					this.Items[0].Selected = true;
					local0 = 0;
				}
				return local0;
			}
			set
			{
				base.SelectedIndex = value;
			}
		}

		public override string ToolTip
		{
			get
			{
				return System.String.Empty;
			}
			set
			{
			}
		}

		public override System.Web.UI.WebControls.BorderStyle BorderStyle
		{
			get
			{
				return base.BorderStyle;
			}
			set
			{
				base.BorderStyle = value;
			}
		}

		public override System.Web.UI.WebControls.Unit BorderWidth
		{
			get
			{
				return base.BorderWidth;
			}
			set
			{
				base.BorderWidth = value;
			}
		}

		public override System.Drawing.Color BorderColor
		{
			get
			{
				return base.BorderColor;
			}
			set
			{
				base.BorderColor = value;
			}
		}

	}
}