How to force visual studio to put content into designer file

Web development model in Visual Studio .Net has changed a lot from its first release. At the moment we have different project types for web development.
Recently I have begun working with a project initially developed many years ago and this project has an old structure. So I tried to convert it to a web project. One problem I faced was not having a seperate file for the designer generated codes, because the support for partial classes added later. It is not actually a problem but I wanted to know how I could easily force the visual studio to put designer generated stuff into a seperate file. After some struggling I found this simple method:

• Just add a file with the name yourfilename.aspx.designer.cs to project.
• Delete the auto generated codes in the main codes file.
• Mark your page's class as partial.
• Then when you save yourfilename.aspx the next time, visual studio will put the generated content into desginger file.