Why does VisualStudio 2013 not find the method after double clicking on the control (Windows Forms)?

Question

Programming

The program has grown a lot and moved the partial part of the Form1 class from the Form1.cs file to a new file, for example NewFile.cs. At the same time, the class is the same - partial class Form1. Among the transferred methods there are also event handlers when a button is clicked, for example.
So now, when double-clicking on a control in the Design window, the studio looks for a method only in the Form1.cs file and stops there, i.e. method for editing does not open. Is it possible to make the search also take place in the NewFile.cs file and the method is automatically opened for editing?

Answer 1

Perhaps adding DependentUpon as described here stackoverflow.com/questions/2485851/winform-partia... will help.
But in my opinion such a transfer is not at all the best solution to the problem.
What did you grow there? Do you have all the business logic right in the form code or what?