How to stop an Loading function on button click?

I have a problem, I have to stop one Loading class on button click. I already checked some forums related to this. But didn't find an exact solution.

For example:

Public Sub LoadDropDown()
   Dim it As Integer
   For it = 0 To 1开发者_C百科000000
      DropDownList1.Items.Add(it)
   Next
End Sub

I have to load the DropDown on Load button click and I have to cancel that on cancel button click.

Since populating the control happens on the server, I can't imagine way to interrupt your method from the client. The whole control is being populated, rendered, and only then sent to the client. You might interrupt the callback using ajax, but then the control wouldn't be returned at all.

An alternative could be to load the contents in chunks with ajax and append them to the control on the client-side.

There is no formal way to do what you're asking, but you should be able to achieve the same result if you refactor your code. If certain content shouldn't be loaded for certain users, do that logic in your code behind before it renders to the page.

Per your response to the other answers...

You could consider doing multiple my_ddl.items.add() calls on a timer. Would involve multiple, separate postbacks / ajax calls. For example:

1) add records for 2 seconds (instead of a fixed number of records at a time)
2) check for session("continue") = "true"
3) add more records for 2 more seconds
4) check session("continue")
...

At some point, user clicks cancel, which assigns "false" to session("continue"). Next time your loop checks session("continue"), it will see that it's false and exit.

This would give you a partially-loaded data control. You might want other code to wipe-out the partial update.

I think you could accomplish this with a Session Variable. Forgive me, but I'll have to provide the example in C#, but I'm sure you can get the general idea of this.

   private bool CancelRequested
        {
            get
            {
                if (Session["CancelRequested"] == null)
                    return false;
                else
                    return (bool)Session["CancelRequested"];
            }
            set
            {
                Session["CancelRequested"] = value;
            }
        }

        public void LoadDropDown()
        {
            for (int it = 0; it <= 1000000; it++)
            {
                if (CancelRequested)
                {
                    CancelRequested = false;
                    break;
                }                    
                //Your logic here
            }
        }

        protected void btnCancelRequest_Click(object sender, EventArgs e)
        {
            CancelRequested = true;
        }

The idea here is that the inital loop checks a Session variable to see if it should continue or break out of the loop. If you have a button on the page that will allow the user to set this Session variable to "true", they can essential communicate to the inital request and cause it to break out of the loop. I'm not sure if this would fully accomplish what you're looking to achieve, but hopefully it helps.