[Solved] Reference a CheckBox within a RadGrid inside a PlaceHolder

1 Answer 28 Views

Checkbox Grid

Wei asked on 25 Feb 2026, 07:15 AM

I am attempting to reference some CheckBoxes withing a RadGrid inside a PlaceHolder.

I have a field that I am retrieving called Block that contains a numerice value. Based on the value I am dynamically creating a number of CheckBoxes in a PlaceHolder equal to that value. I have a Button Click method that is trying to reference the CheckBoxes but it is not working correctly.

This line : Dim BlockCheckBox As CheckBox = DirectCast(phBlocksCheckBox.FindControl("BlockCheckBox_" & cbIndex), CheckBox) is not returning a value.

aspx
<telerik:RadGrid ID="RadGrid1" runat="server" AllowPaging="True" AllowSorting="True" GridLines="None" AllowMultiRowSelection="True" AllowFilteringByColumn="True" EnableLinqExpressions="False">
<MasterTableView AutoGenerateColumns="False">
<PagerStyle AlwaysVisible="True"></PagerStyle>
<Columns>
<telerik:GridClientSelectColumn UniqueName="checkboxColumn1" HeaderTooltip="SELECT All" ShowSortIcon="False" ShowFilterIcon="False" Reorderable="False">
<HeaderStyle Width="30px" />
<telerik:GridBoundColumn DataField="NumberOfBlocks" HeaderText="Block Count" UniqueName="NumberOfBlocks" AllowFiltering="False" Display="False">
<HeaderStyle Width="20px" />
</telerik:GridBoundColumn>
<telerik:GridTemplateColumn DataField="Block" HeaderText="Blocks" UniqueName="BlocksColumn" AllowFiltering="False">
<ItemTemplate>
<asp:PlaceHolder ID="phBlocksCheckBox" runat="server" />
</ItemTemplate>
</telerik:GridTemplateColumn>
</Columns>
</MasterTableView>
<ClientSettings AllowColumnsReorder="True" AllowDragToGroup="True" ReorderColumnsOnClient="True">
<Scrolling UseStaticHeaders="True" />
<Selecting AllowRowSelect="True" />
<ClientEvents OnRowSelected="RowSelected" OnRowDeselected="RowDeselected"></ClientEvents>
</ClientSettings>
</telerik:RadGrid>

vb
Protected Sub Button_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles GenerateCassetteLabelsButton.Click
Dim NumberOfBlocks As Integer = 0

For Each item As GridDataItem In RadGrid1.SelectedItems
NumberOfBlocks = CInt(item("NumberOfBlocks").Text)

Dim phBlocksCheckBox As PlaceHolder = DirectCast(item.FindControl("phBlocksCheckBox"), PlaceHolder)
If phBlocksCheckBox IsNot Nothing Then
HttpContext.Current.Response.Write("phBlocksCheckBox IsNot Nothing ")
For cbIndex As Integer = 1 To NumberOfBlocks
HttpContext.Current.Response.Write("-BlockCheckBoxID : " & "BlockCheckBox_" & cbIndex & " ")
Dim BlockCheckBox As CheckBox = DirectCast(phBlocksCheckBox.FindControl("BlockCheckBox_" & cbIndex), CheckBox)

If BlockCheckBox IsNot Nothing Then
HttpContext.Current.Response.Write("BlockCheckBox IsNot Nothing ")
'Do something with BlockCheckBox.Text
HttpContext.Current.Response.Write("-Block : " & BlockCheckBox.Text & " ")
End If
Next
End If
Next

RadGrid1.Rebind()
End Sub

Protected Sub RadGrid1_ItemDataBound(sender As Object, e As GridItemEventArgs) Handles RadGrid1.ItemDataBound
'Ensure we are dealing with a data item (not header, footer, etc.)
If TypeOf e.Item Is GridDataItem Then
Dim item As GridDataItem = DirectCast(e.Item, GridDataItem)

'Find the placeholder control defined in the ItemTemplate
Dim phBlocksCheckBox As PlaceHolder = CType(item.FindControl("phBlocksCheckBox"), PlaceHolder)

If phBlocksCheckBox IsNot Nothing Then
Dim NumberOfBlocks As Integer = DataBinder.Eval(item.DataItem, "NumberOfBlocks")

'Dynamically create and add checkboxes
If NumberOfBlocks > 0 Then
For BlockIndex As Integer = 0 To NumberOfBlocks - 1
Dim BlockCheckBox As New CheckBox()
BlockCheckBox.ID = "BlockCheckBox_" & (BlockIndex + 1).ToString()
BlockCheckBox.Text = (BlockIndex + 1).ToString()
BlockCheckBox.Checked = True
phBlocksCheckBox.Controls.Add(BlockCheckBox)
phBlocksCheckBox.Controls.Add(New LiteralControl(" "))
Next
End If
End If
End If
End Sub

1 Answer, 1 is accepted

answered on 02 Mar 2026, 06:37 AM

Hi Wei,

Thank you for the provided code snippet.

The issue happens because in ItemCreated the DataItem property is not available during PostBack, so DataBinder.Eval(item.DataItem, "NumberOfBlocks") returns null and no CheckBox controls are created. Since dynamic controls must be recreated on every postback before ViewState is restored, failing to rebuild them results in the PlaceHolder having zero controls when the button click executes.

Using DataKeyNames with GetDataKeyValue or reading the value from the Grid cell ensures the block count is available during ItemCreated. Once the controls are consistently recreated, they will exist in the control tree and can be accessed in Button_Click.

Below you can find the adjusted code snippet:

<telerik:RadGrid ID="RadGrid1" runat="server" AllowPaging="True" OnNeedDataSource="RadGrid1_NeedDataSource" OnItemCreated="RadGrid1_ItemCreated">
    <MasterTableView AutoGenerateColumns="False" DataKeyNames="NumberOfBlocks">
        <Columns>
            <telerik:GridClientSelectColumn UniqueName="checkboxColumn1" />
            <telerik:GridBoundColumn
                HeaderText="Number of blocks"
                DataField="NumberOfBlocks"
                UniqueName="NumberOfBlocks"
                Display="true" />
            <telerik:GridTemplateColumn HeaderText="Blocks">
                <ItemTemplate>
                    <asp:PlaceHolder ID="phBlocksCheckBox" runat="server" />
                </ItemTemplate>
            </telerik:GridTemplateColumn>
        </Columns>
    </MasterTableView>
    <ClientSettings>
        <Selecting AllowRowSelect="true" />
    </ClientSettings>
</telerik:RadGrid>

<telerik:RadButton runat="server" ID="RadButton1" Text="Postback" AutoPostBack="true" OnClick="Button_Click" />

protected void RadGrid1_ItemCreated(object sender, GridItemEventArgs e)
{
    if (e.Item is GridDataItem item)
    {
        PlaceHolder phBlocksCheckBox = (PlaceHolder)item.FindControl("phBlocksCheckBox");

        if (phBlocksCheckBox != null)
        {
            int NumberOfBlocks = Convert.ToInt32(item.GetDataKeyValue("NumberOfBlocks"));

            if (NumberOfBlocks > 0)
            {
                for (int i = 1; i <= NumberOfBlocks; i++)
                {
                    CheckBox cb = new CheckBox();
                    cb.ID = "BlockCheckBox_" + i;
                    cb.Text = i.ToString();
                    cb.Checked = true;

                    phBlocksCheckBox.Controls.Add(cb);
                }
            }
        }
    }
}

protected void Button_Click(object sender, EventArgs e)
{
    foreach (GridDataItem item in RadGrid1.SelectedItems)
    {
        PlaceHolder  placeHolder = (PlaceHolder)item.FindControl("phBlocksCheckBox");

        if (placeHolder != null)
        {
            foreach (Control ctrl in placeHolder.Controls)
            {
                if (ctrl is CheckBox cb && cb.Checked)
                {
                    Response.Write("Checked: " + cb.Text + "<br>");
                }
            }
        }
    }
}

protected void RadGrid1_NeedDataSource(object sender, Telerik.Web.UI.GridNeedDataSourceEventArgs e)
{
    RadGrid1.DataSource = GetDummyData();
}

private DataTable GetDummyData()
{
    DataTable dt = new DataTable();

    dt.Columns.Add("ID", typeof(int));
    dt.Columns.Add("NumberOfBlocks", typeof(int));

    dt.Rows.Add(1, 3);
    dt.Rows.Add(2, 5);
    dt.Rows.Add(3, 2);
    dt.Rows.Add(4, 4);

    return dt;
}

This ensures the CheckBoxes are always found.

Regards,
Vasko
Progress Telerik

Stay tuned by visiting our public roadmap and feedback portal pages! Or perhaps, if you are new to our Telerik family, check out our getting started resources!

Wei

commented on 04 Mar 2026, 12:12 AM

Vasko,

I converted your code to vb and I get error :

Multiple controls with the same ID 'BlockCheckBox_1' were found. FindControl requires that controls have unique IDs.

vb Code :

Protected Sub Button_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadButton1.Click
For Each item As GridDataItem In RadGrid1.SelectedItems
Dim placeHolder As PlaceHolder = DirectCast(item.FindControl("phBlocksCheckBox"), PlaceHolder)

If placeHolder IsNot Nothing Then
For Each ctrl As Control In placeHolder .Controls
If TypeOf ctrl Is CheckBox Then
Dim cb As CheckBox = DirectCast(ctrl, CheckBox)
If cb.Checked Then
Response.Write("Checked: " + cb.Text + " ")
End If
End If
Next
End If
Next
End Sub

Protected Sub RadGrid1_NeedDataSource(sender As Object, e As GridNeedDataSourceEventArgs) Handles RadGrid1.NeedDataSource
RadGrid1.DataSource = GetDummyData()
End Sub

Private Function GetDummyData() As DataTable
Dim dt As New DataTable()
dt.Columns.Add("ID", GetType(Integer))
dt.Columns.Add("NumberOfBlocks", GetType(Integer))

dt.Rows.Add(1, 3)
dt.Rows.Add(2, 5)
dt.Rows.Add(3, 2)
dt.Rows.Add(4, 4)
Return dt
End Function

Protected Sub RadGrid1_ItemCreated(ByVal sender As Object, ByVal e As GridItemEventArgs) Handles RadGrid1.ItemCreated
If TypeOf e.Item Is GridDataItem Then
Dim phBlocksCheckBox As PlaceHolder = DirectCast(e.item.FindControl("phBlocksCheckBox"), PlaceHolder)

If phBlocksCheckBox IsNot Nothing Then
Dim NumberOfBlocks As Integer = DataBinder.Eval(e.Item.DataItem, "NumberOfBlocks")

If NumberOfBlocks > 0 Then
For i As Integer = 1 To NumberOfBlocks
Dim cb As New CheckBox()
cb.ID = "BlockCheckBox_" & i
cb.Text = i.ToString()
cb.Checked = true

phBlocksCheckBox.Controls.Add(cb)
Next
End If
End If
End If
End Sub

Thanks,

Wei

Vasko

commented on 06 Mar 2026, 08:00 AM

Hi Wei,

The error "Multiple controls with the same ID 'BlockCheckBox_1' were found. FindControl requires that controls have unique IDs." occurs because you are generating CheckBoxes with the same ID for each grid row. In ASP.NET, all controls in the same naming container must have unique IDs.

To resolve this, you need to include a unique value from each data row (such as the row's primary key, "ID") in the CheckBox ID. This ensures that each CheckBox across the grid has a unique ID.

Update the RadGrid1_ItemCreated method so the CheckBox ID includes the row's unique "ID" value:

Protected Sub RadGrid1_ItemCreated(ByVal sender As Object, ByVal e As GridItemEventArgs)
    If TypeOf e.Item Is GridDataItem Then
        Dim item As GridDataItem = CType(e.Item, GridDataItem)
        Dim phBlocksCheckBox As PlaceHolder = DirectCast(item.FindControl("phBlocksCheckBox"), PlaceHolder)

        If phBlocksCheckBox IsNot Nothing Then
            Dim NumberOfBlocks As Integer = Convert.ToInt32(item.GetDataKeyValue("NumberOfBlocks"))
            Dim rowId As Integer = Convert.ToInt32(item.GetDataKeyValue("ID"))

            For i As Integer = 1 To NumberOfBlocks
                Dim cb As New CheckBox()
                cb.ID = "BlockCheckBox_" & rowId & "_" & i
                cb.Text = i.ToString()
                cb.Checked = True
                phBlocksCheckBox.Controls.Add(cb)
            Next
        End If
    End If
End Sub

Make sure your grid uses DataKeyNames:

<MasterTableView AutoGenerateColumns="False" DataKeyNames="NumberOfBlocks, ID">

When you need to access a specific CheckBox (e.g., in your Button_Click event), use the same ID pattern:

Protected Sub Button_Click(sender As Object, e As EventArgs)
    For Each item As GridDataItem In RadGrid1.SelectedItems
        Dim placeHolder As PlaceHolder = DirectCast(item.FindControl("phBlocksCheckBox"), PlaceHolder)

        If placeHolder IsNot Nothing Then
            Dim NumberOfBlocks As Integer = Convert.ToInt32(item.GetDataKeyValue("NumberOfBlocks"))
            Dim rowId As Integer = Convert.ToInt32(item.GetDataKeyValue("ID"))

            For i As Integer = 1 To NumberOfBlocks
                Dim cb As CheckBox = DirectCast(placeHolder.FindControl("BlockCheckBox_" & rowId & "_" & i), CheckBox)
                If cb IsNot Nothing AndAlso cb.Checked Then
                    Response.Write("Checked: " & cb.Text & "<br>")
                End If
            Next
        End If
    Next
End Sub

Regards,
Vasko
Progress Telerik