How to see a control in another contentplaceholder?

I'm using a masterpage and having some trouble with my ContentPlaceholders.
I have a combobox(DropDownList1) in the sidemenu content placeholder and in my main placeholder I have a gridview. The gridview is supposed to do a select in the db using the selected value of DropDownList1. When I set up the connection SQL within the datagrid, using the wizard; I select to get a parameter from a control and then I select DropDownList1.

NOW:
When I try to run the page, it returns an error "Exception Details: System.InvalidOperationException: A control with ID 'DropDownList1' could not be found", however if I move DropDownList1 to the main placeholder, everything works perfectly.

How do I get asp.net to see the control sitting in the other placeholder?

use findControl. something like this:
dim myControl = Me.SomeControl.FindControl("dateTimePicker1").FindControl("getDateTb")

you can use findControl for each depth

Quote:

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Originally Posted by jasonwucinski

use findControl. something like this:
dim myControl = Me.SomeControl.FindControl("dateTimePicker1").FindControl("getDateTb")

you can use findControl for each depth

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I tried that, but could not get it to work properly. I finally got it to work by prefixing the contentplaceholder's ID to the id of the control reference

HTML Code:

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<asp:ControlParameter ControlID="LeftMenu$DropDownList1" Name="UserId"
                    PropertyName="SelectedValue" Type="Int32" />

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