Can't open a tabbed project in latest version of IDE


I installed the latest version of the IDE (1.8.16). My previous version was 1.8.10.
The installation went without problems.
I've got a sketch that has 15 tabs in it.
Previously I could click on any of the tabs and the project opened in full.
Now I got a message that the file is not in a folder with the same name. When I click OK it puts the file inside a folder with a same name but I lost all connections to the multiple tabs within that project.
The weird thing is that I have a copy of a previous version where one of the tabs is about 200 bits less in size then the current version. All the rest is the same: Tab-names, size, etc. Both versions are in the same folder and on the same drive.
It's weird that I can open one and it builds up all connectivity between the tabs and the other one is not recognized as a sketch with multiple tabs.
I tried moving files around from a server location to a local drive but that doesn't make a difference.
Has anybody seen this type of behaviour before? And if yes, what did you do so that the file opens as one project?
Cheers and thanks for your help.


Can you group all the tabs into an .ino file? Those usually will open all tabs/scripts of the project.

Please provide a detailed description of what you mean by "click on any of the tabs" so I can make sure I understand your question.

In my Arduino sketches folder I've got a folder called:

In that folder there are 15 .INO files called:

Previously I could click on any of the Axx.ino files and then the whole project opened at once.
Now when I click on any of the Axx.ino files I see a message telling me that the file should be in a folder with the same name. When I click OK i can then see a folder named Axx that contains one Axx.ino file.
When I then click on that file it only opens that sketch and I can't see any other tabs in that sketch.
I hope this clarifies things.
Thanks for your help!

OK, there is your problem. Every Arduino sketch must contain a .ino file that matches the folder name. In this case, that means a file named WeatherStation.ino.

This has always been the case. Your sketch would not work with any version of the Arduino IDE.

So just add that WeatherStation.ino file and I think you'll find that the IDE works as you expect it to. You are not required to put anything in the file if you don't like.

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Hi In0,
That was exactly the problem!
Yes, I had changed the title afterwards and I haven't opened it since. Now that I installed the latest version of the IDE I thought to open a file to see if there were any changes to the IDE, and to my surprise, the sketch didn't open as intended.
Wow, a little quirk in the use of the IDE that I wasn't aware off.
Thanks mate! You've been a great help!


You're welcome. I'm glad to hear it's working now.

This requiremen is a little bit quirky, but there is a reason for it: All the .ino files of the sketch are concatenated into a single file when they are converted to valid C++ before being compiled. For this reason, the order of concatenation is important. The .ino file matching the folder is the primary file that will come first, followed by any other .ino files in alphabetical order. I think this is a slightly more convenient behavior than a purely alphabetical ordering, while allowing for custom arbitrary ordering by the user would require the addition of a metadata file to the sketch and also would add more complexity.

There have been some proposals about lifting this requirement, but I really don't think it's so onerous.

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