In Gridview Set Image Column programatically

Inside RowDataBound event handler for the grid view say
dim img as ImageButton  = e.Row.FindControl(imagebuttonid) as ImageButton
img.ImageURL = ImageString & Session("ClCode") & "/Thumbs...."

A little modification of TechTiger007's solution:
dim img as ImageButton  = e.Row.Cells(i).Controls(0) as ImageButton 'Change "i" to the actual index of the ImageField in GridView.

Thanks for your suggestion. I am getting "End of Statement expected" on "ImageButton":
Code:
Protected Sub dgPInv_RowDatabound(ByVal sender As Object, ByVal e as System.Web.UI.WebControls.GridViewRowEventArgs) Handles dgPInv.RowDataBound
Dim img As ImageButton = e.Row.Cells(12).Controls(0) as ImageButton
img.ImageURL = ImageString & Session("ClCode") & "/Thumbs/{0}"
End Sub

Try this:

Dim img As ImageButton = CType(e.Row.Cells(12).Controls(0), ImageButton)

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Your suggestion sorted the End of statement problem. I am now getting an ArgumentOutOfRangeException.
I understand that "e.Row.Cells(12)" represents the Column in the Gridview. What does ".Controls(0)" represent?
With thanks.

Wait a second. This is an ImageField, not ImageButton. My apology. Use this line:

Dim img As Image = CType(e.Row.Cells(12).Controls(0), Image)

Controls(0) represents the first control in Cell(12).

Make sure the ImageField is the 13th column of your GridView.

Apologies for labouring this problem. I have created the gridview using the SQLDatabase wizard and bound grid to it. I have ImageField as 13th column in grid as follows:
<asp:ImageField DataImageUrlField="PicFile1"></asp:ImageField>
PicFile1 holds the image file name.
I also have following code in code-behind:
Protected Sub dgPInv_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles dgPInv.RowDataBound
Dim img As Image = CType(e.Row.Cells(12).Controls(0), Image)
img.ImageUrl = ImageString & Session("ClCode") & "/Thumbs/"
End Sub
I am still getting System.ArgumentOutOfRangeException was unhandled by user code
  Message="Specified argument was out of the range of valid values.
Parameter name: index"
  ParamName="index"
  Source="System.Web"

How do I refer to the variable file name in the ImageUrl line? I was using {0}.
With thanks
 

Can you post your GridView code (ASPX file)?

Dont seem to be able to send aspx files  within or without zip file.

ASPX file:
<%@ Page Language="VB" MasterPageFile="~/MasterPage.master" AutoEventWireup="false" CodeFile="Invent2.aspx.vb" Inherits="Invent2" title="Constantine Ltd - Inventory Paged" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <asp:Button ID="cmdAll" runat="server" Text="Invent - All" Width="85px" />
    <asp:Button ID="cmdBack" runat="server" Text="Back" Width="85px" />
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:Connectstring %>"
        SelectCommand="cClInv" SelectCommandType="StoredProcedure">
        <SelectParameters>
            <asp:SessionParameter Name="clCode" SessionField="ClCode" Type="String" />
        </SelectParameters>
    </asp:SqlDataSource>
    <asp:GridView ID="dgPInv" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False"
        DataKeyNames="InventNo" DataSourceID="SqlDataSource1" Width="967px">
        <Columns>
            <asp:CommandField ButtonType="Button" ShowSelectButton="True" />
            <asp:BoundField DataField="Location" HeaderText="Location" SortExpression="Location" />
            <asp:BoundField DataField="clInventNo" HeaderText="Client InvNo" SortExpression="clInventNo" />
            <asp:BoundField DataField="clInventNo2" HeaderText="Cat No" SortExpression="clInventNo2" />
            <asp:BoundField DataField="ArtistMaker" HeaderText="Artist" SortExpression="ArtistMaker" />
            <asp:BoundField DataField="ShortDesc" HeaderText="Title" SortExpression="ShortDesc" />
            <asp:BoundField DataField="iDate" HeaderText="Date" SortExpression="iDate" />
            <asp:BoundField DataField="Medium" HeaderText="Medium" SortExpression="Medium" />
            <asp:BoundField DataField="Height" HeaderText="Length" SortExpression="Height" />
            <asp:BoundField DataField="Width" HeaderText="Width" SortExpression="Width" />
            <asp:BoundField DataField="Depth" HeaderText="Height" SortExpression="Depth" />
            <asp:BoundField DataField="AcquPriceEquiv" DataFormatString="{0:C}" HeaderText="Value"
                HtmlEncode="False" SortExpression="AcquPriceEquiv" />
            <asp:ImageField DataImageUrlField="PicFile1"></asp:ImageField>
        </Columns>
        <HeaderStyle BackColor="Navy" Font-Size="Small" ForeColor="White" />
        <PagerSettings Position="TopAndBottom" Mode="NumericFirstLast" FirstPageText="First &amp;lt;&amp;lt;" LastPageText="Last &amp;gt;&amp;gt;" />
        <PagerStyle Font-Size="Small" />
    </asp:GridView>
  </asp:Content>
 
Vb file:
Partial Class Invent2
    Inherits System.Web.UI.Page
    Private ImageString As String = ConfigurationSettings.AppSettings("ImagePath")
 
    Protected Sub dgPInv_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles dgPInv.RowDataBound
        Dim img As Image = CType(e.Row.Cells(12).Controls(0), Image)
        img.ImageUrl = ImageString & Session("ClCode") & "/Thumbs/"
    End Sub
    Protected Sub dgPInv_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles dgPInv.SelectedIndexChanged
        Dim index As Integer = dgPInv.SelectedIndex
        Response.Redirect("InvPart.aspx?txtInvNo=" + Me.dgPInv.DataKeys(index).Value.ToString)
    End Sub
 
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Session("Private") = False Then Response.Redirect("Default.aspx")
    End Sub
 
    Protected Sub cmdAll_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdAll.Click
        Response.Redirect("Invent.aspx?txtClCode=" + Session("ClCode"))
    End Sub
 
    Protected Sub cmdBack_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles cmdBack.Click
        Response.Redirect("Account.aspx?txtClCode=" + Session("ClCode"))
    End Sub
End Class

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OK, you will need to check if the row is a DataRow before you can use FindControl

Protected Sub dgPInv_RowDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs) Handles dgPInv.RowDataBound 
If (e.Row.RowType = DataControlRowType.DataRow) Then
  Dim img As Image = CType(e.Row.Cells(12).Controls(0), Image) 
  img.ImageUrl = ImageString & Session("ClCode") & "/Thumbs/" 
End If
End Sub 

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Sorry, I should have caught the fact earlier that you are missing "If (e.Row.RowType.." in your RowDataBound event handler.

I am still not getting the image file name into img.imageurl. The properties of the image in the grid is coming through as the path only. How do I get the file name from the data source?
I am nearly there - I am very grateful to you.

In your original post, you have this:
iPicFile = ImageString & Session("ClCode") & "/Thumbs/{0}"

Where do you do this?

I was using:
DataImageUrlFormatString="Images/A009/Thumbs/{0}">
in the properties of the image column in the grid
and
iPicFile = ImageString & Session("ClCode") & "/Thumbs/{0}"
in the code-behind
I have set in the properties of the ImageField in the grid:
<asp:ImageField DataImageUrlField="PicFile1"></asp:ImageField> and am trying to add the value of PicFile1 to the iPicFile string.

Done