I ran the code upgrade tool and it left some issues unresolved most of them are deprecated classes for instance:
Class CMS.FormControls.CMSBaseForm was removed. You can use class CMS.FormControls.AbstractBasicForm instead.
However in my custom web part I use Bizform which as I can see in CMS.FormControls.dll, v7.0.4997.7757 inherits from CMSBaseForm. I didn't find AbstractBasicForm in CMS.Formcontrols namespace, though, I only found BasicForm.
I think there are BizForms in Kentico 8 too so that shouldn't be a problem.
How can I solve issues like this?
Or do I need to solve them before upgrade?
This one looks similar:
Class CMS.UIControls.UniGridPager was removed. You can use class UIPager instead.
Or this one in \CMSFormControls\Basic\UploadControlLimited.ascx.cs:
Class method System.String CMS.FormControls.BasicForm.GetFileNameForUploader(System.String) was removed. The type or member is no longer supported. Please contact Kentico support if you need to find a replacement.