Files on a one aspx page?

I think many developers don't know exactly how many files on a one aspx page. Sometimes, that is causes more problems arise.

Exactly, one aspx page have 3 file:
- 1 layout: example.aspx
- 1 code behind: example.aspx.c
- and 1 designer: example.aspx.designer.cs

Some people will say, where is designer file? I can't see it.... Microsoft doesn't want to show you designer file. Because if you don't understand what it is, maybe you can change it and make it wrong and aspx page will fail and can't run. So, Visual Studio will generate it automatic and hidden it.

Have any ideal about it? And is it necessary or not? In some cases you will don't need it and you will make it by yourself.

Do you want more information?