Lately, I've been working on a project in NetBeans using the GUI editor that's built in. Before I noticed that it generated an XML ".form" file that didn't appear in the Project Explorer Pane which makes sense. Earlier I was working on the form in the "Design" tab when it notified me about 15 updates. I just updated without reading anything which was probably a bad idea but when I restarted the IDE, it showed my GUI ".class" file and ".form" file separately in the Project Explorer and I couldn't switch between "Source" and "Design". I also noticed that the generated code that was usually not editable was now editable.
P.S. I'm able to create a new frame just fine and the design editor still works with new frame
I have encounter the same problem and I have solved it.
The key in this problem, I think, is particular plugins for JFrame in Netbeans are not active after updating, so we only need to activate them. The easiest way to achieve this is create a new JFrame class, so in this progress, NetBeans can activate all relevant plugins for us. Finally, restart NetBeans, then everything would be fine.
Thank you very much for all of you that you give me some idea and clues in this situation:)
Work on a similar problem led me to this discussion concerning Guarded blocks inside form Java source file. I'm not sure it's related to your situation, but it may help you recover.
If you are trying to recover the lost state of the backing xml for the form I don't know what to tell you.
This has happened to me, but I tend to highly componentize the forms (break up the forms into little pieces), which makes this not such a big deal. Have you tried the NetBeans forums? You might get better luck there:
Nevermind, simple solution.
I finally decided that, after plenty of tinkering, to restart the IDE which I should have though of first. The Java SE Plugin must have crashed or something, anyway it's fixed.
Thanks for the help!
Or just right click on the corresponding .form file and select open. The Design tab/editor reestablishes.
来源：https://stackoverflow.com/questions/5426365/cant-edit-jframe-form-after-netbeansupdate