Question

I have following asp.net code but it gives error when I change dropdown selected index:

<asp:UpdatePanel>
      <ContentTemplate>
        <asp:DropDownList ID="drp" runat="server" AutoPostBack="true" OnSelectedIndexChanged="drp_SelectedIndexChanged">
          <asp:ListItem Text="ABC" Value="ABC"></asp:ListItem>
          <asp:ListItem Text="DEF" Value="DEF"></asp:ListItem>
        </asp:DropDownList>
        <asp:Panel ID="pnl" runat="server">
        </asp:Panel>
        <asp:Button ID="Button1" runat="server" Text="Submit" OnClick="Button1_Click" />
      </ContentTemplate>
      <Triggers>
        <asp:PostBackTrigger ControlID="drp" />
        <asp:PostBackTrigger ControlID="Button1" />
      </Triggers>
    </asp:UpdatePanel>

Now made one function for create textbox and get textbox value into lable as following way

protected void drp_SelectedIndexChanged(object sender, EventArgs e)

{
  if (drp.SelectedIndex != 0)
  {
    ViewState["controls"] = true;
    CreateTextbox(drp.SelectedIndex);
  }

}

private void CreateTextbox(int Number)
{
  try
  {
    TextBox txtTextbox;
    Label lbltxtTextbox;
    for (int i = 0; i < Number; i++)
    {
      txtTextbox = new TextBox();
      txtTextbox.ID = "txtbox" + i;
      lbltxtTextbox = new Label();
      lbltxtTextbox.ID = "lbltxtbox" + i;
      pnl.Controls.Add(txtTextbox);
      pnl.Controls.Add(lbltxtTextbox);
    }
  }
  catch (Exception ex)
  {
  }
}

private void GetTextboxvalue(int Number)
{
  try
  {
    TextBox txtTextbox;
    Label lbltxtTextbox;
    for (int i = 0; i < Number; i++)
    {
      txtTextbox = (TextBox)pnl.FindControl("txtbox" + i);
      lbltxtTextbox = (Label)pnl.FindControl("lbltxtbox" + i);
      lbltxtTextbox.Text = txtTextbox.Text;
    }
  }
  catch (Exception ex)
  {
  }
}

protected void Button1_Click(object sender, EventArgs e)
{
  GetTextboxvalue(drp.SelectedIndex);
}
protected void Page_Load(object sender, EventArgs e)
{

  if (ViewState["controls"] != null)
    if (drp.SelectedIndex != 0)
    {
      CreateTextbox(drp.SelectedIndex);
    }



}

error is:

Multiple controls with the same ID 'txtbox0' were found. FindControl requires that controls have unique IDs.

Answer 1

GUID

Change the following line

txtTextbox.ID = "txtbox" + sequentialId;

to below line

txtTextbox.ID = "txtbox" + Guid.NewGuid().ToString("N");

---

You can follow the same approach in remaining places.