Develop Reference

dealing with GridView and Custom Validation, both client and serverside

I'm not quite sure how to solve this problem.
What I'm trying to do:
Go through a gridview with multiple rows, and force the user to enter in specific values if certain textboxes or drop down lists are left on the default value.
What I tried:
Tried client side requirements, by use of the focusout event in javascript. Focus goes onto these fields depending on the previous selections users make, that part works. My code:
var row = $(this).closest('tr');
var text = $(row).find("input[name*='txtCurriculum']").val('enter lesson/unit name here');
var ddl = $(row).find("select[name*='ddlCurrAdditions']");
$(ddl).focusout(function () {
if (ddl.val == "-select curriculum name-") {
$(ddl).focus();
alert("select a curriculum name before moving on");
}
});
$(text).focusout(function () {
if (text.val == 'enter lesson/unit name here') {
$(text).focus();
alert('enter in a lesson or unit name before moving on');
}
});
It never fired properly. the ddl focusout would fire, but wouldn't stop firing until I exited and went back to the page. the text focusout would never fire.
Tried server side validation, with the custom validation feature.
protected void cv1_ServerValidate(object source, ServerValidateEventArgs args)
{
CustomValidator cv = ((CustomValidator)(source));
GridViewRow gvr;
//if (FormCGrid.Rows)
foreach (GridViewRow row in FormCGrid.Rows)
{
//string ddl = ((DropDownList)row.FindControl("ddlCurrAdditions")).SelectedItem.Text;
string txtC = ((TextBox)row.FindControl("txtCurriculum")).Text;
bool ddl = ((DropDownList)row.FindControl("ddlCurrAdditions")).Visible;
if (txtC == "enter lesson/unit name here")
{
args.IsValid = false;
cv.ErrorMessage = string.Format("Please enter the Additional program name on row {0}", row.RowIndex);
}
else if (ddl == true)
{
cv.ErrorMessage = string.Format("Enter your lesson or unit for the curriculum selected on row {0}", row.RowIndex);
args.IsValid = false;
}
}
}
I tried to loop through the rows of the gridview here, checking the named dropdown for visibility (hidden until another dropdownlist reveals it, dependent on the value chosen there) and the textbox for the default value, yet this did not work either. It never fired at all. Any suggestions welcome.
I am generally ok with most programming/coding issues, but I find that working with the asp.net gridview, all of my techniques get thrown out the window.

Ok, there are two ways to do this, and you can use js quite easy here. However, lets go with a 100% server side code. I think sticking to server side code is easier.
Next up? I actually STONG suggest to use a listview in place of a gridview WHEN you plan to edit data. The reason is simple - the ListView does not require those "irratating" "item template" over and over for each asp.net control you want to drop/have in that grid display. Now to be fair, say 2-3 controls - then grid view is ok, but for more, then I really find that the listview starts to win here big time (no need for the item template).
The "trick" with listview is of course to setup a datasoruce on the web page, let it generate the markup, and then blow out (delete) all templates except for the item template. And then delete the datasourc1 item on the page, and remove the datasource1 setting from the list view.
However, lets go with the grid view - this will thus be some what "more messy"
So, we going to fill out the grid - and say we want a city combo box - MUST be selected. And lets toss in a basic check for say LastName also must be entered.
So, we have a city combo box (database driven). And say lets toss in a drop down for a hotel rating (1-5) - but that's only 5 choices - so we have that dropdown with the list in mark-up. (so two combo examples to show how this works).
So, say we have a grid like this, and we hit save, we get this result:
Now, of course we would fancy up that message box area. And in fact, we could VERY easy drop in jQuery.UI and make that cute div on the right appear in a dialog box (and we can trigger that box + jQuery.UI dialog display even from our server side code behind - but lets try and keep this short - but I would fancy up that error message area).
Ok, first the markup:
Just a simple grid, but "a bit messy" due to those "item Templates - (if you not figured this out, I really dislike those template things!!! - and with listview you don't need them!! - just drop in pure clean asp.net controls for the grid). Anyway:
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="ID">
<Columns>
<asp:BoundField DataField="ID" HeaderText="ID" InsertVisible="False" ReadOnly="True" SortExpression="ID" />
<asp:TemplateField HeaderText="HotelName" >
<ItemTemplate><asp:TextBox id="HotelName" runat="server" Text='<%# Eval("HotelName") %>' /></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="FirstName" >
<ItemTemplate><asp:TextBox id="FirstName" runat="server" Text='<%# Eval("FirstName") %>' /></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="LastName" >
<ItemTemplate><asp:TextBox id="LastName" runat="server" Text='<%# Eval("LastName") %>' /></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="City">
<ItemTemplate>
<asp:DropDownList ID="cboCity" runat="server" DataTextField="City"
DataValueField = "City" Width="110px">
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Active">
<ItemTemplate><asp:CheckBox id="Active" runat="server" Checked = '<%# Eval("Active") %>' /></ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Rating">
<ItemTemplate>
<asp:DropDownList ID="cboRating" runat="server" SelectedValue = '<%# Eval("Rating") %>' >
<asp:ListItem Value="1">Poor</asp:ListItem>
<asp:ListItem Value="2">Just Ok</asp:ListItem>
<asp:ListItem Value="3">Ok</asp:ListItem>
<asp:ListItem Value="4">Good</asp:ListItem>
<asp:ListItem Value="5">Excellent</asp:ListItem>
</asp:DropDownList>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
</div>
<div id="ErrorDialog" style="display:normal;float:left;padding-left:30px;width:20%" runat="server">
<asp:TextBox ID="txtErrors" runat="server" TextMode="MultiLine" Style="width:100%" Rows="20" ></asp:TextBox>
</div>
<div style="clear:both;padding-top:20px">
<asp:Button ID="cmdSave" runat="server" Text="Save" />
<asp:Button ID="cmdUnDo" runat="server" Text="UnDo" Style="margin-left:20px"/>
</div>
Ok, now on SO? Gee, that is about the total max markup I would post in one shot - beyond above, we approach the "not very nice" post territory.
Ok, so lets look at the code to load up this grid. We have this code:
public class EditHotelsG : System.Web.UI.Page
{
private DataTable rstTable = new DataTable();
private DataTable rstCity = new DataTable();
protected void Page_Load(object sender, System.EventArgs e)
{
if (System.Web.UI.Page.IsPostBack == false)
{
ErrorDialog.Visible = false;
LoadGrid();
ViewState["rstTable"] = rstTable;
ViewState["rstCity"] = rstCity;
}
else
{
rstTable = ViewState["rstTable"];
rstCity = ViewState["rstCity"];
}
}
public void LoadGrid()
{
// load up our drop down list from database (city)
string strSQL;
strSQL = "SELECT City from tblCity Order by City";
using (SqlCommand cmdSQL = new SqlCommand(strSQL, new SqlConnection(My.Settings.TEST3)))
{
cmdSQL.Connection.Open();
rstCity.Load(cmdSQL.ExecuteReader);
// now load up main grid view
strSQL = "SELECT ID, FirstName, LastName, HotelName, City, Active, Rating from tblHotels ORDER BY HotelName";
cmdSQL.CommandText = strSQL;
rstTable.Load(cmdSQL.ExecuteReader);
GridView1.DataSource = rstTable;
GridView1.DataBind();
}
}
protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
// set combo box data source
if (e.Row.RowType == DataControlRowType.DataRow)
{
// setup city drop down list
DropDownList cboDrop = e.Row.FindControl("cboCity");
cboDrop.DataSource = rstCity;
cboDrop.DataBind();
cboDrop.Items.Insert(0, new ListItem(string.Empty)); // add blank row
cboDrop.Text = rstTable.Rows(e.Row.RowIndex).Item("City").ToString;
}
}
}
Ok, now that is not all that much code. And a good part was setting up that combo box. Since the cbo box (dropdown list) was database driven, then we have to bind + setup for each row. So, that cost us a good chunk of our coding time.
Note however how we persist the database soruce (table). We do that, since we want to with A LOT LESS code, update the whole database behind in ONE shot. By peristing that table, then we
Transfer data from Grid to table
Save the table to database in one shot
So, this reduces our coding efforts by a truckload.
The code to save our data, thus becomes this gem:
(and note how we ALSO put in our validation code).
protected void cmdSave_Click(object sender, EventArgs e)
{
// pull gride rows back to table.
bool bolDataOk = true;
txtErrors.Text = "";
foreach (GridViewRow rRow in GridView1.Rows)
{
int RecordPtr = rRow.RowIndex;
DataRow OneDataRow;
OneDataRow = rstTable.Rows(RecordPtr);
OneDataRow.Item("HotelName") = rRow.FindControl("HotelName") as TextBox.Text;
OneDataRow.Item("FirstName") = rRow.FindControl("FirstName") as TextBox.Text;
OneDataRow.Item("LastName") = rRow.FindControl("LastName") as TextBox.Text;
OneDataRow.Item("City") = rRow.FindControl("cboCity") as DropDownList.Text;
OneDataRow.Item("Active") = rRow.FindControl("Active") as CheckBox.Checked;
OneDataRow.Item("Rating") = rRow.FindControl("cboRating") as DropDownList.SelectedValue;
// check for missing City, or LastName
if (IsDBNull(OneDataRow("City")) | OneDataRow("City") == "")
{
bolDataOk = false;
if (txtErrors.Text != "")
txtErrors.Text += Constants.vbCrLf;
txtErrors.Text += "Missing City on row = " + (rRow.RowIndex + 1).ToString;
}
if (IsDBNull(OneDataRow("LastName")) | OneDataRow("LastName") == "")
{
bolDataOk = false;
if (txtErrors.Text != "")
txtErrors.Text += Constants.vbCrLf;
txtErrors.Text += "Missing lastName on row = " + (rRow.RowIndex + 1).ToString;
}
}
ErrorDialog.Visible = !(bolDataOk);
// now send table back to database with updates
if (bolDataOk)
{
string strSQL = "SELECT ID, FirstName, LastName, City, HotelName, Active, Rating from tblHotels WHERE ID = 0";
using (SqlCommand cmdSQL = new SqlCommand(strSQL, new SqlConnection(My.Settings.TEST3)))
{
cmdSQL.Connection.Open();
SqlDataAdapter daupdate = new SqlDataAdapter(cmdSQL);
SqlCommandBuilder cmdBuild = new SqlCommandBuilder(daupdate);
daupdate.Update(rstTable);
}
}
}
Now, once again, that above code snip is a wee bit long - and is aobut the max size of a code snip for SO. I would perhaps consider breaking out that above last code into 2 or even 3 routines.
but, all in all, the above shows quite a few tricks, and approaches here.
As noted, I was going to post how you can/could verify using client side code, ,but the OVER ALL idea of saving back the whole grid with one database update? Well, I would use that trick with a listview, gridview, and even if I was doing client side js verification? I will still use the bulk of the above design pattern.
And the un-do button? Well, I never finished that part - but it would just call the same code as the first page load (postback - false, and you would simply re-bind the grid from the database source for the un-do button.

Session in not passed between pages c#

I'm working with VS 2013 and Mysql, in one of my pages I put select query in a gridview in this view and I have a button for each row so that if I press a row button I have a new window opening that has the colum Id (which is the first colum ) from the gridview.
the grid view button code:
<Columns>
<asp:TemplateField ><ItemTemplate><asp:Button ID="gridbutton" runat="server" Text="Plus de détails" OnClientClick="basicPopup();return false;" RowIndex='<%# Container.DisplayIndex %>' OnClick="button_click" /></ItemTemplate></asp:TemplateField>
</Columns>
the code of the button_click method:
protected void button_click(object sender, EventArgs e)
{
Button gridbutton = sender as Button;
int rowIndex = Convert.ToInt32(gridbutton.Attributes["RowIndex"]);
string n = "l'index" + rowIndex + "";
Session["idProjet"] = GridView1.Rows[rowIndex].Cells[2].Text;
//string idProjet = Convert.ToString(Session["idProjet"]);
// Alert.Show(idProjet);
}
I just used the two last lines to make sure that I'm getting the value, and I'm getting the right value.
And this is the code from the second page where I want to get the session value:
protected void Page_Load(object sender, EventArgs e)
{
string idProjet = Convert.ToString(Session["idProjet"]);
Alert.Show(idProjet);
}
But all I'm getting is an empty result.

In you button code you have both onclientclick and click event.
In you clickclick event I guest you are opening the different page. Note that client click executes first. So the new page already gets opened. Your server side event executes later. That is why the session is not available in the new form.
<asp:Button ID="gridbutton" runat="server" Text="Plus de détails" OnClientClick="basicPopup();return false;" RowIndex='<%# Container.DisplayIndex %>' OnClick="button_click" />
In this case you have to pass the idProject as query string to the new page.

data pager in listview Issue

I have a listview where in I placed datapager as follows.
I am using SQl datasource and binding the records to ListView.
asp:ListView runat="server" ID="ListView1" DataKeyNames="ProductId,GameName" DataSourceID="GameTable" OnItemCommand="On_Select_Item"
and datapager in the LayoutTemplate
And in the item template I am placing a button, when clicked it calls a method where i am trying to fetch DatakeyName values. It is working fine in first page when pager is given, However when moved to other page in the pager, it is throwing me an exception.
Here is the button click code,
protected void On_Select_Item(object sender, ListViewCommandEventArgs e)
{
if (String.Equals(e.CommandName, "AddtoCart"))
{
//checks if the user is logged in
if (User.Identity.IsAuthenticated)
{
ListViewDataItem dataItem = (ListViewDataItem)e.Item;
DropDownList dl = e.Item.FindControl("DropDownList") as DropDownList;
String val="";
if (dl != null)
{
val = dl.SelectedValue; //Get the selected value from DropDownList
}
String price = Convert.ToString(e.CommandArgument).Trim(); //Get the price for the selected game.
-------------Exception is thrown at below line ---------
string ProductId =
ListView1.DataKeys[dataItem.DataItemIndex]["ProductId"].ToString(); //Product Id for the selected game.
string GameName = ListView1.DataKeys[dataItem.DataItemIndex]["GameName"].ToString(); //gamename
...............................
.............................
}

Define a grid first (you can change the control name to listView but the implementation is the same )
<asp:GridView runat="server" ID="grdResult"
CellPadding="2"
OnPageIndexChanging="grdResult_PageIndexChanging"
GridLines="None"
Width="100%"
AllowSorting="True"
AllowPaging="True"
Then in the bottom define a data source
<asp:SqlDataSource ID="sqlGridData" runat="server"></asp:SqlDataSource>
now in the code behind load your sqlGridData control with data (it accepts many parameters like datatable, odbcrecordset you can use .provider property mentioned here http://tinyurl.com/bllyjsz ) if you have static data them you even mention at the design time (as done here http://tinyurl.com/c8b6mbh)
private void BindDataGrid()
{
sqlGridData.Provider = dataReader;
grdResult.DataSourceID = "xmlGridData";
//grdResult.PageIndex = 0;
}
Try this and do let me know if you have any query.

Gridview Row Events not firing in UserControl

I've got a pretty strange problem with my usercontrols that I'm working with. I'm coding some user controls to be used in a DotNetNuke module.
Basically I have a UserControl on my page that holds some controls and then there is a Placeholder where I am loading in a UserControl that has a GridView placed in it.
Basically here is my page structure
<asp:Panel runat="server" ID="pnlServiceType" Visible="false">
<uc:ServiceType runat="server" ID="ServiceType" />
</asp:Panel>
Within that user control are some form elements and then the following:
<asp:PlaceHolder runat="server" ID="phServices" />
That placeholder then has a user control added to it like so:
<p class="header"><asp:Label runat="server" ID="lblServiceHeader" Font-Bold="true" /></p>
<asp:GridView runat="server" ID="gvServices" AlternatingRowStyle-BackColor="#eaeaea" BorderStyle="None" GridLines="None"
AutoGenerateColumns="false" CellPadding="6" Width="100%" EnableViewState="false" OnRowEditing="gvServices_RowEditing">
When the user picks something in the DropDownList, I'm clearing the controls out of the Placeholder, and re-adding just a single UserControl for the set of records for whatever type they've picked like so
_serviceID = e.Value;
//Clear the controls out of the placeholder
phServices.Controls.Clear();
//Reset the count of grids for the OnInit() method
Session["GridCount"] = 0;
if (e.Value != "NULL")
{
PopulateServicesGrid(_service.GetServicesByFormType(Convert.ToInt32(e.Value)));
}
else
{
PopulateServicesGrid(_service.GetServicesByClient(Convert.ToInt32(_client)));
}
And the PopulateServicesGrid method:
private void PopulateServicesGrid(List<NOAService> services)
{
//Creates a LINQ grouping based on the Billing Codes
//Allows a super easy creation of grids based on the grouped billing codes
var query = services.Select(service => service.BillingCode).Distinct();
foreach (string code in query)
{
var servicesByCode = services.Where(service => service.BillingCode == code).ToList();
ServicesGrid servicesGrid = LoadControl("~/DesktopModules/LEL Modules/NOA/ServicesGrid.ascx") as ServicesGrid;
Label lblServiceHeader = servicesGrid.FindControl("lblServiceHeader") as Label;
GridView gvServices = servicesGrid.FindControl("gvServices") as GridView;
phServices.Controls.Add(servicesGrid);
servicesGrid.ID = code;
lblServiceHeader.Text = servicesByCode[0].FormTypeName;
gvServices.DataSource = servicesByCode;
gvServices.DataBind();
Session["GridCount"] = phServices.Controls.Count;
}
}
And on my ServiceType UserControl, on the PageInit, I'm readding the ServiceGrid usercontrol so that my grids show up across postbacks and aren't lost from the Placeholder
void NOAServiceType_Init(object sender, EventArgs e)
{
for (int i = 0; i < Convert.ToInt32(Session["GridCount"]); i++)
{
ServicesGrid servicesGrid = LoadControl("~/DesktopModules/LEL Modules/NOA/ServicesGrid.ascx") as ServicesGrid;
phServices.Controls.Add(servicesGrid);
}
}
The grids populate successfully and everything seems to work just fine. But for some reason, on my GridView, I have a CommandField of
<asp:CommandField ShowEditButton="true" ItemStyle-HorizontalAlign="Right" EditText="Edit" UpdateText="Update"
EditImageUrl="~/images/LELModules/appbar.edit.rest.png" CancelImageUrl="~/images/LELModules/appbar.close.rest.png" UpdateImageUrl="~/images/LELModules/appbar.check.rest.png"
ButtonType="Image" CausesValidation="false" />
When I click my Edit command on the Grid row, nothing happens. My grid doesn't lose its rows, the control is still there, everything seems like it should be ok. The RowEditing event doesn't fire until I click it a second time.
Any idea why this might be occuring?
UPDATE: I've managed to figure out that my SelectedIndexChanged handlers are effectively resetting the DataSource on the Grid contained by the UserControl when they are readded to the PlaceHolder. When the CommandField (Edit) is clicked though, the Init fires for the UserControl that holds the placeholder
ServiceType UserControl < `Init` fires here
-Form elements
-Placeholder which holds
--UserControl with GridView
The Init method loads up new instances of the UserControl and adds them to the PlaceHolder, but the DataSource is null. With EnableViewState=true it looks like the data is still bound, but if I handle PreRender, I can see that the DataSource on my gvServices | null
Is it even possible to edit rows like this on a GridView that is being added dynamically to a PlaceHolder over and over?
FIXED I found out what the issue was after referring to this article
http://www.west-wind.com/weblog/posts/2006/Feb/24/Overriding-ClientID-and-UniqueID-on-ASPNET-controls
It got me thinking, what if the IDs were getting changed? The controls are way nested. So I went and put a watch on the GridView's ID, ClientID, and UniqueID just to see. When the Control is loaded on my Init handler, it's assigned a super generic ID when it's added.
private void PopulateServicesGrid(List<NOAService> services)
{
//Creates a LINQ grouping based on the Billing Codes
//Allows a super easy creation of grids based on the grouped billing codes
var query = services.Select(service => service.BillingCode).Distinct();
foreach (string code in query)
{
var servicesByCode = services.Where(service => service.BillingCode == code).ToList();
ServicesGrid servicesGrid = LoadControl("~/DesktopModules/LEL Modules/NOA/ServicesGrid.ascx") as ServicesGrid;
Label lblServiceHeader = servicesGrid.FindControl("lblServiceHeader") as Label;
GridView gvServices = servicesGrid.FindControl("gvServices") as GridView;
phServices.Controls.Add(servicesGrid);
**servicesGrid.ID = code;**
lblServiceHeader.Text = servicesByCode[0].FormTypeName;
gvServices.DataSource = servicesByCode;
gvServices.DataBind();
Session["GridCount"] = phServices.Controls.Count;
}
}
I was setting the ID as something else. So when I was hitting the Edit RowCommand on my grid, it was reloading the controls again on Init and the IDs were being changed back from my custom set code (T2020, pulled from my database) to the generic ID again, it didn't know how to fire the event.
I hope this helps someone as I've lost at least 12 hours fixing this problem.

How to hide a column (GridView) but still access its value?

I have a GridView with a DataSource (SQL Database). I want to hide a column, but still be able to access the value when I select the record. Can someone show me how to do this?
This is the column I want to hide and still want to access its value:
<asp:BoundField DataField="Outlook_ID" HeaderText="OutlookID" />
I tried everything to hide the column (property Visible="false"), but I can't access its value.

<head runat="server">
<title>Accessing GridView Hidden Column value </title>
<style type="text/css">
.hiddencol
{
display: none;
}
</style>
<asp:BoundField HeaderText="Email ID" DataField="EmailId" ItemStyle-CssClass="hiddencol" HeaderStyle-CssClass="hiddencol" >
</asp:BoundField>
ArrayList EmailList = new ArrayList();
foreach (GridViewRow itemrow in gvEmployeeDetails.Rows)
{
EmailList.Add(itemrow.Cells[YourIndex].Text);
}

If I am not mistaken, GridView does not hold the values of BoundColumns that have the attribute visible="false". Two things you may do here, one (as explained in the answer from V4Vendetta) to use Datakeys. Or you can change your BoundColumn to a TemplateField. And in the ItemTemplate, add a control like Label, make its visibility false and give your value to that Label.

Define a style in css:
.hiddencol { display: none; }
Then add the ItemStyle-CssClass="hiddencol" and the HeaderStyle-CssClass="hiddencol" attribute to the grid field:
<asp:BoundField DataField="ID" HeaderText="ID" ItemStyle-CssClass="hiddencol" HeaderStyle-CssClass="hiddencol" ClientIDMode="Static" />

You can use DataKeys for retrieving the value of such fields, because (as you said) when you set a normal BoundField as visible false you cannot get their value.
In the .aspx file set the GridView property
DataKeyNames = "Outlook_ID"
Now, in an event handler you can access the value of this key like so:
grid.DataKeys[rowIndex]["Outlook_ID"]
This will give you the id at the specified rowindex of the grid.

You can do it programmatically:
grid0.Columns[0].Visible = true;
grid0.DataSource = dt;
grid0.DataBind();
grid0.Columns[0].Visible = false;
In this way you set the column to visible before databinding, so the column is generated.
The you set the column to not visible, so it is not displayed.

If you do have a TemplateField inside the columns of your GridView and you have, say, a control named blah bound to it. Then place the outlook_id as a HiddenField there like this:
<asp:TemplateField HeaderText="OutlookID">
<ItemTemplate>
<asp:Label ID="blah" runat="server">Existing Control</asp:Label>
<asp:HiddenField ID="HiddenOutlookID" runat="server" Value='<%#Eval("Outlook_ID") %>'/>
</ItemTemplate>
</asp:TemplateField>
Now, grab the row in the event you want the outlook_id and then access the control.
For RowDataBound access it like:
string outlookid = ((HiddenField)e.Row.FindControl("HiddenOutlookID")).Value;
Do get back, if you have trouble accessing the clicked row. And don't forget to mention the event at which you would like to access that.

You can make the column hidden on the server side and for some reason this is different to doing it the aspx code. It can still be referenced as if it was visible. Just add this code to your OnDataBound event.
protected void gvSearchResults_DataBound(object sender, EventArgs e)
{
GridView gridView = (GridView)sender;
if (gridView.HeaderRow != null && gridView.HeaderRow.Cells.Count > 0)
{
gridView.HeaderRow.Cells[UserIdColumnIndex].Visible = false;
}
foreach (GridViewRow row in gvSearchResults.Rows)
{
row.Cells[UserIdColumnIndex].Visible = false;
}
}

Leave visible columns before filling the GridView. Fill the GridView and then hide the columns.

Here is how to get the value of a hidden column in a GridView that is set to Visible=False: add the data field in this case SpecialInstructions to the DataKeyNames property of the bound GridView , and access it this way.
txtSpcInst.Text = GridView2.DataKeys(GridView2.SelectedIndex).Values("SpecialInstructions")
That's it, it works every time very simple.

I have a new solution hide the column on client side using css or javascript or jquery.
.col0
{
display: none !important;
}
And in the aspx file where you add the column you should specify the CSS properties:
<asp:BoundField HeaderText="Address Key" DataField="Address_Id" ItemStyle-CssClass="col0" HeaderStyle-CssClass="col0" > </asp:BoundField>

I used a method similar to user496892:
SPBoundField hiddenField = new SPBoundField();
hiddenField.HeaderText = "Header";
hiddenField.DataField = "DataFieldName";
grid.Columns.Add(hiddenField);
grid.DataSource = myDataSource;
grid.DataBind();
hiddenField.Visible = false;

I found this solution, an elegant(IMO) quick 2 parter.
1.
On your gridview, add a column as normal, no need to do anything differently:
<asp:BoundField DataField="AccountHolderName" HeaderText="Account Holder"
ReadOnly="true"/>
You can keep the header text if this is useful to you for later processing.
2.
In the rowdatabound method for the grid hide the header, footer and row for that column index:
if (e.Row.RowType == DataControlRowType.Header)
{
e.Row.Cells[10].Visible = false;
}
if (e.Row.RowType == DataControlRowType.Footer)
{
e.Row.Cells[10].Visible = false;
}
if (e.Row.RowType == DataControlRowType.DataRow)
{
e.Row.Cells[10].Visible = false;
}

You can do it code behind.
Set visible= false for columns after data binding .
After that you can again do visibility "true" in row_selection function from grid view .It will work!!

I searched a lot but no luck. The most of them was working with some errors. Finally I used this code and it worked for me.
probably you should change 1 to some other value. for me I would hide second col.
protected void FoundedDrGridView_RowDataBound(object sender, GridViewRowEventArgs e)
{
if(e.Row.RowType!=DataControlRowType.Pager)e.Row.Cells[1].Visible = false;
}

I just set the width to 0. and it works.
columns.AddFor(m => m.Id).Name("hide-id").Width(0);

When I want access some value from GridView before GridView was appears.
I have a BoundField and bind DataField nomally.
In RowDataBound event, I do some process in that event.
Before GridView was appears I write this:
protected void GridviewLecturer_PreRender(object sender, EventArgs e)
{
GridviewLecturer.Columns[0].Visible = false;
}