Mixing single file and code behind user controls in one project

I have a user control with code behind that references a single file user control. It calls one of the properties of the single file control, but I get a compiler error:
Error      4 'SearchString' is not a member of 'ucontrols.templates.templatebase'
Now ucontrols.templates.templatebase is the base class of the single file user control, but the property is in the control itself. Is there a way to make this work without making the second control use code behind?
 
Thanks,
Boris Zakharin
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