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Re: Custom DataGridColumn DataGridItems not saving to ViewState. Not Visible on Postback

ricky.arora

2/8/2004 3:59:00 AM

I have similar kinda problem. Actually, I have a checkbox in my
datagrid which I created dynamically. Now when the user checks the
Checkboxes and hits submit, the Datagrid is recreated. I think i have
to add the checkbox value to ViewState. Is that correct.
Will appreciate your help.

Best regards!

googleGroupResponder@illexcascade.com (Jay Walker) wrote in message news:<406ec8f.0401281552.ea4af45@posting.google.com>...
> I created a custom DataGridColumn based on Marcie Robillard's MSDN
> Article:
>
> Creating Custom Columns for the ASP.NET Datagrid
> http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/creatingcustomc...
>
> The problem I am having is that the data in the custom datagridcolumn
> is not saved to viewstate and after postback, the column does not
> contain data.
>
> Any idea's?
>
> I simplified the code so that the error is easy to reproduce.
> Here is the code: (notice that the CustomImage that is standalone on
> the page and the CustomImage that is embedded in a template column are
> visible after postback.)
>
> I can send a zip file of the project on request.
>
> -=-=-=-=- CustomColumn.cs (begin) -=-=-=-=-
> using System;
> using System.Data;
> using System.Web.UI.WebControls;
> using System.Web.UI;
>
> namespace PostbackError
> {
> public class CustomColumn : System.Web.UI.WebControls.DataGridColumn
> {
> public override void
> InitializeCell(System.Web.UI.WebControls.TableCell cell, int
> columnIndex, System.Web.UI.WebControls.ListItemType itemType)
> {
> //if the grid is using sorting, the the header will contain a
> DataGridLinkButton
> //the functionality is set by the base class initializecell.
> base.InitializeCell (cell, columnIndex, itemType);
> switch (itemType)
> {
> case ListItemType.Item:
> case ListItemType.AlternatingItem:
> cell.DataBinding += new EventHandler(OnDataBinding);
> break;
> }}
>
> private void OnDataBinding(object sender, EventArgs e)
> {
> TableCell cell = sender as TableCell;
> DataGridItem dgi = cell.NamingContainer as DataGridItem;
> DataRowView drv = dgi.DataItem as DataRowView;
> //hardcoded for this example
> string image = "arrow.gif";
> if (image.Length == 0)
> return;
>
> CustomImage ri = new CustomImage();
> cell.Controls.Add(ri);
> TrackViewState();
> string tooltip = "Help";
> ri.ImageUrl = image;
> ri.ToolTip = tooltip;
> }}}
> -=-=-=-=- CustomColumn.cs (end) -=-=-=-=-
>
>
> -=-=-=-=- CustomImage.cs (begin) -=-=-=-=-
> using System;
> using System.ComponentModel;
> using System.IO;
> using System.Text;
> using System.Text.RegularExpressions;
> using System.Web.UI;
> using System.Web.UI.Design;
>
> namespace PostbackError
> {
> public class CustomImage : System.Web.UI.WebControls.Image
> {
> private string _imagePath = string.Empty;
>
> public CustomImage():base()
> {
> _imagePath = string.Empty;
> }
>
> [
> Browsable(true),
> Category("Appearance"),
> Description("Image to be displayed when the mouse is not over the
> image")
> ]
> public new string ImageUrl
> {
> get { return (string)ViewState["riImageUrl"]; }
> set { ViewState["riImageUrl"] = value; }
> }
>
> [
> Browsable(true),
> Category("Appearance"),
> Description("Image to be displayed when the mouse is over the
> image")
> ]
> public string MouseOverImageUrl
> {
> get { return (string)ViewState["MouseOverImageUrl"]; }
> set { ViewState["MouseOverImageUrl"] = value; }
> }
>
> [
> Browsable(true),
> Category("Navigation"),
> Description("The url to navigate to")
> ]
> public string NavigateUrl
> {
> get { return (string)ViewState["NavigateUrl"]; }
> set { ViewState["NavigateUrl"] = value; }
> }
>
> [
> Browsable(true),
> Category("Appearance"),
> DefaultValue(true),
> Description("Use a MouseOver Image derived from the Image name.
> (i.e. image.gif -> image_ovr.gif)")
> ]
> public bool UseMouseOverImage
> {
> get
> {
> string property = "UseMouseOverImage";
> if (ViewState[property] == null)
> {
> object obj = _GetDefaultValue(property);
> if (obj != null)
> ViewState[property] = (bool)obj;
> }
> return (bool)ViewState[property];
> }
> set { ViewState["UseMouseOverImage"] = value; }
> }
>
>
> override protected void OnPreRender(EventArgs e)
> {
> base.OnPreRender(e);
> string s = base.ImageUrl;
> base.ImageUrl = _imagePath + ImageUrl;
> s = base.ImageUrl;
> string mouseOver = _GetImageMouseOver();
> if (mouseOver != null && UseMouseOverImage)
> {
> Attributes.Add("onmouseover", "this.src='" + _imagePath +
> mouseOver + "'");
> Attributes.Add("onmouseout", "this.src='" + _imagePath + ImageUrl
> + "'");
> }
> }
>
> /// <summary>
> /// Render this control to the output parameter specified.
> /// </summary>
> /// <param name="output"> The HTML writer to write out to </param>
> protected override void Render(HtmlTextWriter output)
> {
> bool bWriteAnchor = NavigateUrl != null && NavigateUrl.Length > 0;
> string s1 = base.ImageUrl;
> base.ImageUrl = _imagePath + ImageUrl;
>
> StringWriter sw = new StringWriter();
> HtmlTextWriter buffer = new HtmlTextWriter(sw);
>
> if (bWriteAnchor)
> {
> buffer.AddAttribute(HtmlTextWriterAttribute.Href, NavigateUrl);
> buffer.RenderBeginTag(HtmlTextWriterTag.A);
> }
>
> base.Render(buffer);
>
> if (bWriteAnchor)
> buffer.RenderEndTag();
>
> string s = sw.ToString();
> output.Write(s);
> }
>
> private object _GetDefaultValue(string propertyName)
> {
> System.ComponentModel.AttributeCollection attributes =
> TypeDescriptor.GetProperties(this)[propertyName].Attributes;
> DefaultValueAttribute myAttribute =
> (DefaultValueAttribute)attributes[typeof(DefaultValueAttribute)];
> if (myAttribute != null)
> return myAttribute.Value;
> else
> return null;
> }
>
> private string _GetImageMouseOver()
> {
> if (MouseOverImageUrl != null) return MouseOverImageUrl;
>
> StringBuilder sb = new StringBuilder();
> Regex re = new Regex(@"\.");
> //Image should be like "media.gif" over image should be
> "media_ovr.gif"
> //and have a part left and right of the period
> //if the entry is not in this format, then the entry is invalid
> //so return null
> if (ImageUrl == null) return null;
>
> string[] sa = re.Split(ImageUrl);
> if (sa.Length != 2) return null;
> return sa[0] + "_ovr." + sa[1];
> }
> }
>
> public class CustomImageDesigner:ControlDesigner
> {
> public override string GetDesignTimeHtml( )
> {
> return "<h6>" + this.ID + "</h6>";
> }
> }
> }
> -=-=-=-=- CustomImage.cs (end) -=-=-=-=-
>
>
> -=-=-=-=- WebForm1.aspx (begin) -=-=-=-=-
> <%@ Register TagPrefix="cust" Namespace="PostbackError"
> Assembly="PostbackError" %>
> <%@ Page language="c#" Codebehind="WebForm1.aspx.cs"
> AutoEventWireup="false" Inherits="PostbackError.WebForm1"
> trace="true"%>
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
> <HTML>
> <HEAD>
> <title>WebForm1</title>
> <meta name="GENERATOR" Content="Microsoft Visual Studio .NET 7.1">
> <meta name="CODE_LANGUAGE" Content="C#">
> <meta name="vs_defaultClientScript" content="JavaScript">
> <meta name="vs_targetSchema"
> content="http://schemas.microsoft.com/intellisense/ie5...
> </HEAD>
> <body>
> <form id="Form1" method="post" runat="server">
> <br>
> <cust:CustomImage id="ciTest" runat="server" ImageUrl="arrow.gif"
> Border="1" />
> <br>
> <br>
> <asp:DataGrid id="DataGrid1" runat="server" CellSpacing="1"
> CellPadding="0" GridLines="None" AutoGenerateColumns="False"
> AllowSorting="True" Width="100%">
> <Columns>
> <asp:TemplateColumn>
> <HeaderTemplate>
> <asp:CheckBox id="ckSelectAll" runat="server"
> AutoPostBack="false" />
> </HeaderTemplate>
> <ItemTemplate>
> <asp:CheckBox id="ckSelect" runat="server" AutoPostBack="false"
> />
> </ItemTemplate>
> </asp:TemplateColumn>
> <cust:CustomColumn HeaderText="L" ItemStyle-BackColor="#ff0000"/>
> <asp:TemplateColumn>
> <ItemTemplate>
> <cust:CustomImage id="ciGridImage" runat="server"
> ImageUrl="arrow.gif" Border="1" />
> </ItemTemplate>
> </asp:TemplateColumn>
> <asp:BoundColumn DataField="col1" HeaderText="Col1">
> <ItemStyle HorizontalAlign="Left" />
> </asp:BoundColumn>
> <asp:BoundColumn DataField="col2" HeaderText="Col2">
> <ItemStyle HorizontalAlign="Left" />
> </asp:BoundColumn>
> </Columns>
> </asp:DataGrid>
> <asp:Button id="Button1" runat="server" Text="Button"></asp:Button>
> </form>
> </body>
> </HTML>
> -=-=-=-=- WebForm1.aspx (end) -=-=-=-=-
>
>
> -=-=-=-=- WebForm1.aspx.cs (begin) -=-=-=-=-
> using System;
> using System.Collections;
> using System.ComponentModel;
> using System.Data;
> using System.Drawing;
> using System.Web;
> using System.Web.SessionState;
> using System.Web.UI;
> using System.Web.UI.WebControls;
> using System.Web.UI.HtmlControls;
>
> namespace PostbackError
> {
> /// <summary>
> /// Summary description for WebForm1.
> /// </summary>
> public class WebForm1 : System.Web.UI.Page
> {
> protected System.Web.UI.WebControls.Button Button1;
> protected PostbackError.CustomImage ciTest;
> protected System.Web.UI.WebControls.DataGrid DataGrid1;
>
> ICollection CreateDataSource()
> {
> DataTable dt = new DataTable();
> DataRow dr;
>
> dt.Columns.Add(new DataColumn("col1", typeof(Int32)));
> dt.Columns.Add(new DataColumn("col2", typeof(string)));
>
> for (int i = 0; i < 5; i++)
> {
> dr = dt.NewRow();
>
> dr[0] = i;
> dr[1] = "Item " + i.ToString();
>
> dt.Rows.Add(dr);
> }
>
> DataView dv = new DataView(dt);
> return dv;
> }
>
> private void Page_Load(object sender, System.EventArgs e)
> {
>
> if (!IsPostBack)
> {
> // Load this data only once.
> DataGrid1.DataSource= CreateDataSource();
>
> DataGrid1.DataBind();
> }
> }
>
> #region Web Form Designer generated code
> override protected void OnInit(EventArgs e)
> {
> //
> // CODEGEN: This call is required by the ASP.NET Web Form Designer.
> //
> InitializeComponent();
> base.OnInit(e);
> }
>
> /// <summary>
> /// Required method for Designer support - do not modify
> /// the contents of this method with the code editor.
> /// </summary>
> private void InitializeComponent()
> {
> this.Load += new System.EventHandler(this.Page_Load);
>
> }
> #endregion
>
> }
> }
> -=-=-=-=- WebForm1.aspx.cs (end) -=-=-=-=-