At runtime, the form's asp.net webforms form changes, see that I have the component id on my machine.
Local example:
<asp:HiddenField runat="server" ID="MenuSelecionado" value="processo"/>
After execution, it looks like this:
<input type="hidden" name="ctl00$ContentPlaceHolder1$MenuSelecionado" id="ctl00_ContentPlaceHolder1_MenuSelecionado" value="processo">
I wonder if you have any way to keep the ID or use another property in his place.
You have yes, you can use ClientIDMode
<asp:HiddenField runat="server" ID="MenuSelecionado" value="processo" ClientIDMode="Static"/>
You can see more about it at documentation
Another alternative:
Keep track like this:
<asp:HiddenField runat="server" ID="MenuSelecionado" Value="processo" />
And in Page_Load:
MenuSelecionado.ID = "MenuSelecionado";
The problem this way is that it will add the text "MainContent" before, thus getting the element
<input name="ctl00$MainContent$Bla" id="MainContent_MenuSelecionado" value="processo" type="hidden">
I'm going to do some testing if I find another way