You might have come across this problem in your travels, I know I have. Basically if you’re using jQuery UI’s Dialog and have a <form runat=”server”> inside of that dialog, your postback is not going to work. What’s going on?

jQuery UI is taking the dialog DIV content and moving it outside of the <form runat=”server”> tag. This makes your postback no longer function as expected.

Luckily we can fix this fairly easily with jQuery itself.

var dlg = $('#divMyDialog').dialog({
                    autoOpen: false,
                    modal: true,
                    width: 400,
                    resizable: false,
                    overlay: {
                        background: "black",
                        opacity: 0.5    
                    }
                });
dlg.parent().appendTo(jQuery('form:first'));

The special logic lies in the last line—using the reference to our created dialog, we get the parent container and move it back to the first <form> on the page. After that, all is well.

If you’ve used ASP.Net for any amount of time, you quickly realize how much it loves to dump into the viewstate. Now, I’m not claiming I’m a saint in this area, but I have been learning as I go to recognize what operations will fill the viewstate and work to prevent them.

One trick I learned recently is to re-bind your DropDownList on every postback, inside of the DropDownList’s Init event handler. You can also pull in the postback value from the Request.Form collection and set the DropDownList’s SelectedValue to what it should be. Observe the following example:

Protected Sub ddlMyDropDownList_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles ddlMyDropDownList.Init
    Dim db = New MyDataContext()

    Dim q = From s In db.States _
            Order By s.StateName _
            Select New ListItem(s.StateName, s.StateAbbrev)

    ddlMyDropDownList.Items.AddRange(q.ToArray())

    Dim r = Request(ddlMyDropDownList.UniqueID)
    If r IsNot Nothing Then ddlMyDropDownList.SelectedValue = r
End Sub

Don’t forget to set “EnableViewState=False” on your DropDownList.

I’ve been hit by this a few times, and it’s darn confusing at first, but it makes sense (kinda.)

In ASP.Net, if you reference a control’s .Visible property, it not only checks if it’s been set to Visible = True, but also if it’s parent control is Visible = True. Only then will it return a “True” value back to you.

For example, let’s say you have a PlaceHolder, and inside the PlaceHolder you add a Label control:

   1: <asp:PlaceHolder ID="phParent" runat="server">

   2:     <asp:Label ID="lblChild" runat="server" />

   3: </asp:PlaceHolder>

And then in your code, you write:

   1: phParent.Visible = False

   2: lblChild.Visible = True

   3: Response.Write(lblChild.Visible)

Your response is going to be “False” because the Label’s parent control is not visible.

Just thought I’d share this as a warning to anyone else who might get tripped up on it.