Reference non asp checkbox in code behind

Question

I am trying to reference a non-asp check box in C# code behind. The reason the checkbox is not an asp element, is it gets auto-generated on the fly, rather than being a part of the website. So far I have the following relevant aspx:

<asp:Table ID="myTable" runat="server" Width="100%"> 
    <asp:TableRow>
        <asp:TableCell>A</asp:TableCell>
        <asp:TableCell>B</asp:TableCell>
        <asp:TableCell>C</asp:TableCell>
        <asp:TableCell>D</asp:TableCell>
        <asp:TableCell>E</asp:TableCell>
    </asp:TableRow>
</asp:Table>
<asp:LinkButton runat="server" ID="TEST" CssClass="btn btn-default pull-right" OnClick="TEST_Click">
    TEST <i class="m-icon-swapright m-icon-white"></i>
</asp:LinkButton>

And the C# code behind is:

    public void GenerateTable()
    {
        int i = 0;
        bool[] box = {true, false, true, false, true};
        List<TableRow> tRows = new List<TableRow>();
        TableRow newRow = new TableRow();
        tRows.Add(newRow);
        foreach (var check in box)
            {
                TableCell tempCell = new TableCell();
                if (check)
                {
                    tempCell.Text = "<input type=\"checkbox\" id=\"chk" + i + "\" >";
                }
                else
                {
                    tempCell.Text = "<input type=\"checkbox\" id=\"chk" + i + "\" checked>";
                }
                tRows[0].Cells.Add(tempCell);
                i++;
        }

        foreach (TableRow row in tRows)
        {
            myTable.Rows.Add(row);
        }
    }


    public void TEST_Click(object sender, EventArgs e)
    {

        HtmlInputCheckBox chkbox = (HtmlInputCheckBox)FindControl("chk1");
        if (chkbox != null)
        {
            if (!chkbox.Checked)
            {
                MessageBox.Show("Checked");
            }
            else
            {
                MessageBox.Show("NOT Checked");
            }
        }
        else
            MessageBox.Show("NOTHING :(");
    }

chkbox is always null :(.

Please wrap it in like an <asp:Panel ID="Pnl" runat="server"> first and use Pnl.FindControl("chk1"); — Rob
– Rob, Commented Aug 26, 2018 at 6:41
Is this a stand-alone .aspx page, or does it have a master page? The latter has a tendency to change the generated ID. Can you edit an example of the rendered input? — Tieson T.
– Tieson T., Commented Aug 26, 2018 at 6:41
I have tried Robs suggestion, and it worked but only with checkboxes manually added in the aspx. It does have a master page, I have updated how the checkboxes are added. Thanks. — meowcat
– meowcat, Commented Aug 30, 2018 at 22:32

pfx · Accepted Answer · 2018-09-02 17:37:28Z

You'll need to change two things.

In order to find a checkbox via FindControl it must be part of the pages control collection, which means you have to add a CheckBoxcontrol.

CheckBox c = new CheckBox { ID = "chk"  + i };                
tempCell.Controls.Add(c);

The dynamically added CheckBox control is part of the control collection of the Table, so you'll have to search for it there instead of on the page.

CheckBox chkbox = (CheckBox)this.myTable.FindControl("chk1");

Below you find a full update of your code.

protected void Page_Load(object sender, EventArgs e)
{
    GenerateTable();
}


public void GenerateTable()
{
    int i = 0;
    bool[] box = {true, false, true, false, true};
    List<TableRow> tRows = new List<TableRow>();
    TableRow newRow = new TableRow();
    tRows.Add(newRow);
    foreach (var check in box)
    {
        TableCell tempCell = new TableCell();
        CheckBox c = new CheckBox { ID = "chk"  + i };
        c.Checked = check;
        tempCell.Controls.Add(c);                    

        tRows[0].Cells.Add(tempCell);
        i++;
    }

    foreach (TableRow row in tRows)
    {
        myTable.Rows.Add(row);
    }
}


public void TEST_Click(object sender, EventArgs e)
{
    CheckBox chkbox = (CheckBox)this.myTable.FindControl("chk1");
    if (chkbox != null)
    {
        if (!chkbox.Checked)
        {
            MessageBox.Show("Checked");
        }
        else
        {
            MessageBox.Show("NOT Checked");
        }
    }
    else 
    {           
        MessageBox.Show("NOTHING :(");                           
    }
}

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