Question

I add some div into a panel on server side, when the page is generated, and I add a ID for each one :

HtmlGenericControl divContainerInside = new HtmlGenericControl("div");
divContainerInside.ID = "inside_" + m_oIDCategoria + "_" + numero;

than, on postback (after re-creating them), I cycle them :

foreach (HtmlGenericControl divInside in myPanel.Controls.OfType<HtmlGenericControl>())
{
    Response.Write(divInside.ID);
}

all is ok! But, if I remove that divContainerInside.ID when I generate it, I get a NullException cycling them. Why?

Answer 1

I guess you get NullException when you try to read the ID, which you haven’t set.

If you change your code like this, you’ll get the value:

foreach (HtmlGenericControl divInside in myPanel.Controls.OfType<HtmlGenericControl>())
{
    Response.Write(divInside.ClientID);
}

PS: I don’t know if you have got this line of code:

myPanel.Controls.Add(divContainerInside);

If you want to find out more about web controls you can read this article and this.