How to dynamically and incrementally add controls to a container - asp.net

Question

I thought this was straight forward, but i have a link button, and I do this in the click event:
myContainer.Controls.Add( new FileUpload());
I expect 1 new file control upload to be spawned in the container for each click, however, I always get 1. What do I need to do to have multiple file upload controls?

Answer 1

Since the control was added dynamically, it does not survive the postback. This means that you have to add the file upload (or any other dynamically added control) again in the preinit event to be able to have its values populated and to use it later on in the page life cycle.
Sounds like you are trying to be able to upload multiple files. You may want to add the file uploads with jQuery and use the Request.Files property to get them on the back-end.

Answer 2

I agree with Becuzz's answer. Try this, there are better ways to do it, but this might help as well:
Add this to the "Load" event of your page
if (!IsPostBack) {
Session["UploadControls"] = null;
}
if (Session["UploadControls"] != null) {
if (((List<Control>)Session["UploadControls"]).Count > 0) {
foreach ( ctrl in (List<Control>)Session["UploadControls"]) {
files.Controls.Add(ctrl);
}
}
}
And also add this to the PreInit portion of your page:
string ButtonID = Request.Form("__EVENTTARGET");
if (ButtonID == "Button1") {
FileUpload NewlyAdded = new FileUpload();
List<Control> allControls = new List<Control>();
if (Session["UploadControls"] != null) {
if (((List<Control>)Session["UploadControls"]).Count > 0) {
foreach ( ctrl in (List<Control>)Session["UploadControls"]) {
allControls.Add(ctrl);
//Add existing controls
}
}
}
if (!allControls.Contains(NewlyAdded)) {
allControls.Add(NewlyAdded);
}
Session["UploadControls"] = allControls;
}
And add this to your HTML. This can be anything of course:
<div id="files" runat="server">
</div>
I use the "__EVENTTARGET" value to know what caused the postback, so that you don't get unwanted Upload controls.
Good luck, and hopefully this helps.
Hanlet