Can't find dynamically created TD in code behind - asp.net

Question

I have created a dynamic table in my code behind which loads up on page load. I have created a button which when clicked I need to add a <div> to specific <td> in the table. However, it is not finding my <td> element using the id. What am I doing wrong?
Function CalendarRefresh(Day As Integer, MonthDays As Integer)
Dim iDay As Integer = 1
Dim TableID As Integer
Dim TDCount As Integer = 0
Dim FullTDCount As Integer = 0 '42
Dim StringHtml As New StringBuilder
Dim DaysInMonth As Integer = MonthDays
clsWork.GetUnscheduledWork()
Dim ClientName = "Terence Creighton" ' Test Replace with DB Value
Dim JobName = "Install Job"
' Top structure of table
StringHtml.Append("<table id='calendar' runatserver='server'>")
StringHtml.Append("<tr class='weekdays'>")
StringHtml.Append("<th scope='col'>Sunday</th>")
StringHtml.Append("<th scope='col'>Monday</th>")
StringHtml.Append("<th scope='col'>Tuesday</th>")
StringHtml.Append("<th scope='col'>Wednesday</th>")
StringHtml.Append("<th scope='col'>Thursday</th>")
StringHtml.Append("<th scope='col'>Friday</th>")
StringHtml.Append("<th scope='col'>Saturday</th>")
StringHtml.Append("</tr>")
StringHtml.Append("<tr Class='days'>")
If Day > 1 Then
Do While iDay < (Day)
' add Previous month style
StringHtml.Append("<td class='day other-month'>")
StringHtml.Append("</td>")
iDay = iDay + 1
TDCount = TDCount + 1
FullTDCount = FullTDCount + 1
Loop
End If
For i As Integer = 1 To DaysInMonth
If TDCount = 7 Then
StringHtml.Append("</tr>")
StringHtml.Append("<tr class='days'>")
TDCount = 0
FullTDCount = FullTDCount + 1
i = i - 1
Else
StringHtml.Append("<td class='day' ")
StringHtml.Append("id='")
StringHtml.Append(i)
StringHtml.Append("' Runat='server'>")
StringHtml.Append("<div class='date'>")
StringHtml.Append(i)
StringHtml.Append("</div>")
'StringHtml.Append("<div id='")
'StringHtml.Append(i)
'StringHtml.Append("' Runat='server'>")
'StringHtml.Append("<div Class='panel panel-primary' draggable='true'>")
'StringHtml.Append("<div Class='panel-heading'>")
'StringHtml.Append(ClientName)
'StringHtml.Append("</div>")
'StringHtml.Append("<div Class='panel-body'>")
'StringHtml.Append(JobName)
'StringHtml.Append("</div>")
'StringHtml.Append("</div>")
StringHtml.Append("</div>")
StringHtml.Append("</td>")
TDCount = TDCount + 1
FullTDCount = FullTDCount + 1
End If
Next
StringHtml.Append("</tr>")
StringHtml.Append("</table>")
Return StringHtml.ToString
End Function
Public Sub ScheduledJobs()
Dim StringHtml As New StringBuilder
Dim ClientName As String
Dim JobName As String
Dim Work = clsWork.GetUnscheduledWork()
For Each i As Integer In Work.Rows.Count
ClientName = Work.Rows(i).Items("ClientName").ToString
JobName = Work.Rows(i).Items("JobName").ToString
ID = i.ToString
StringHtml.Append("<div class='panel panel-primary' draggable='true' ondragstart='OnDragStart' ondrop='OnDrop' ")
StringHtml.Append("id='")
StringHtml.Append(ID)
StringHtml.Append("'>")
StringHtml.Append("<div class='panel-heading'>")
StringHtml.Append(ClientName)
StringHtml.Append("</div>")
StringHtml.Append("<div class='panel-body'>")
StringHtml.Append(JobName)
StringHtml.Append("</div>")
Next
Dim MyTable As HtmlTable = Page.FindControl("calendar")
Dim MyCell As HtmlTableCell
MyCell.ID = "19"
If MyCell Is Nothing Then
messageResponse = "Tablecell not found"
Else
MyCell.InnerHtml = StringHtml.ToString
End If
End Sub
Private Sub cmdLoadJobs_ServerClick(sender As Object, e As EventArgs) Handles cmdTry.ServerClick
ScheduledJobs()
End Sub
I am expecting find the td with the ID and add the html string in the ("td Element").innerhtml. I have tried various combinations of findcontrol but all turns up empty

Answer 1

You have to create real dynamic controls. Here a very basic example of how to interact with a dynamically created table.
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack == false)
{
//do not create dynamic control in an ispostback check
}
//create some table and it's rows and cells. note the assignent of an ID
Table table = new Table()
{
ID = "MyTable1"
};
TableRow row = new TableRow()
{
ID = "MyRow1"
};
TableCell cell = new TableCell()
{
ID = "MyCell1",
Text = "My 1st cell"
};
//add the cell to the row
row.Controls.Add(cell);
//add the row to the table
table.Controls.Add(row);
//add the table to the page
PlaceHolder1.Controls.Add(table);
}
protected void Button1_Click(object sender, EventArgs e)
{
//use findcontrol to locate the cell
TableCell cell = PlaceHolder1.FindControl("MyCell1") as TableCell;
//interact with it
cell.Text = "Cell Found!";
}

Answer 2

I see this:
StringHtml.Append("<table id='calendar' runatserver='server'>")
While it's certainly fine to push raw html to a page in the browser by building an html string, you cannot create server controls this way. You won't be able to access anything in that html from your code behind. The runat='server' part is first of all keyed wrong, but would be worthless even if written correctly. By the time you're in the Page_Load event, everything that looks for the runat='server' attribute has already finished.