After several test I found that this that I did previously in another project is not working. In fact, a project I worked on a few months ago shows me this error of not showing the design tab.
I am using:
Version: 2020-12 (4.18.0) Build id: 20201210-1552
Some screenshots of what I said before.
¿Is this a bug or I am doing some wrong? A similar problem exists with WindowBuilder (08/2020-09/2020) but were fixed in previous version according comments. Thanks
EDIT: Solved
According to the screenshot, you opened the MainFraime.java
file with the regular Java editor instead of the WindowBuilder editor.
Right-click the file and choose Open With > WindowBuilder Editor (see WindowBuilder Pro User Guide - Editing Existing Windows).
Please note, since Eclipse 2020-12 (4.18) Open With > ... no longer remembers the chosen editor to open that file next time. This means double-clicking a file always opens the file with the default editor which is for *.java
files the regular Java editor, not the WindowBuilder editor.