VB.net Mouse click single cell of gridview, change backcolor and output cell position (col and row) to textbox

Question 1

Basically: in the code behind you set an onclick script for each cell, passing the coordinates of the cell and the textbox for the results.

In the aspx the js script writes the coordinates of the clicked cell in the textbox, iterates all the cells in the table setting the color to white and finally sets the backgrond color to red only for the clicked cell

aspx code:

<%@ Page Language="vb" AutoEventWireup="false" CodeBehind="TestEvidenziazione.aspx.vb" Inherits="Web_Test_2010.TestEvidenziazione" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script type="text/javascript">
        function highlight(my_row, cell, textbox) {
            document.getElementById("<%=txtCellSelected.ClientID%>").value = my_row + ',' + cell;
            var table = document.getElementById("<%=GridView1.ClientID%>");
            for (var i = 0, row; row = table.rows[i]; i++) {
                //iterate through rows
                //rows would be accessed using the "row" variable assigned in the for loop
                for (var j = 0, col; col = row.cells[j]; j++) {
                    //iterate through columns
                    //columns would be accessed using the "col" variable assigned in the for loop
                        col.style.backgroundColor = '#ffffff';
                    if (i == my_row && j == cell) {
                        col.style.backgroundColor = '#ff0000';
                    }
                }
            }
        }
    </script>
</head>
<body>
    <form id="form1" runat="server">

    <div>
        <asp:TextBox ID="txtCellSelected" runat="server"></asp:TextBox>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="true" ShowHeader="false">

    </asp:GridView>
    </div>
    </form>
</body>
</html>

vb.net code:

Public Class TestEvidenziazione
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        LoadData()
    End Sub

    Private Sub LoadData()
        Dim list As New ArrayList
        Dim row1 As New myRowClass
        Dim row2 As New myRowClass
        Dim row3 As New myRowClass

        row1.a = "0,0"
        row1.b = "0,1"
        row1.c = "0,2"

        row2.a = "1,0"
        row2.b = "1,1"
        row2.c = "1,2"

        row3.a = "2,0"
        row3.b = "2,1"
        row3.c = "2,2"
        list.Add(row1)
        list.Add(row2)
        list.Add(row3)
        GridView1.DataSource = list
        GridView1.DataBind()

    End Sub

    Private Class myRowClass
        Public Property a As String
        Public Property b As String
        Public Property c As String
    End Class

    Private Sub GridView1_PreRender(sender As Object, e As System.EventArgs) Handles GridView1.PreRender
        For index_row = 0 To GridView1.Rows.Count - 1
            If GridView1.Rows(index_row).RowType = DataControlRowType.DataRow Then
                For index_cell = 0 To GridView1.Rows(index_row).Cells.Count - 1
                    GridView1.Rows(index_row).Cells(index_cell).Attributes("onclick") = "highlight(" & index_row.ToString & "," & index_cell.ToString & ", " & txtCellSelected.ClientID & "); "
                Next
            End If
        Next
    End Sub
End Class

Question 2

Note: the following code is not tested. You may need to modify it to meet your needs.

In answer to your other question - reverting the cell back to its original color - you can add a custom attribute with the necessary information.

You could modify Andrea's code as follows:

Private Sub GridView1_PreRender(sender As Object, e As System.EventArgs) Handles GridView1.PreRender
    For index_row = 0 To GridView1.Rows.Count - 1
        If GridView1.Rows(index_row).RowType = DataControlRowType.DataRow Then
            For index_cell = 0 To GridView1.Rows(index_row).Cells.Count - 1
                GridView1.Rows(index_row).Cells(index_cell).Attributes("onclick") = "highlight(" & index_row.ToString & "," & index_cell.ToString & ", " & txtCellSelected.ClientID & "); "
                ' Change begins here...
                Dim l_bg = GridView1.Rows(index_row).Cells(index_cell).BackColor
                GridView1.Rows(index_row).Cells(index_cell).Attributes.Add( _
                    "data-defaultBackground", _
                    String.Format( "#{0:X2}{1:X2}{2:X2}{3:X2}", l_bg.A, l_bg.R, l_bg.G, l_bg.B )
                )
            Next
        End If
    Next
End Sub

Then switch this javascript code:

col.style.backgroundColor = '#ffffff';

to this:

col.style.backgroundColor = col.getAttribute("data-defaultBackground");

This code uses the HTML5 data attribute standard. See John Resig's blog post, HTML 5 data- Attributes, for more information. This standard is relatively new and support may be spotty.

Note that you may have some trouble with getAttributes.

I got the code for converting a Color to a hex string from an answer by VirtualBlackFox

Please consider awarding the answer/bounty to Andrea, as s/he did all the real work.

Question 3

I would solve this problem by using jQuery in combination with the answers given by Cyborg and Andrea. jQuery will give you more readable javascript code.