WindowBuilder Crash

[C4J]

I have encountered a problem and found the solution.

First of all I must confess to using ChatGPT to create the code - I know - the shame the shame of it.

Anyway - moving on.

I jave a JFrame and it has a button added to it (see code fragment below).

The code which I have commented out was created by AI and I've had to comment it out and replace with my version.

If I open the JFrame in design view with the original code then Eclipse just freezes and I have to force the task to close.

I am running Eclipse 2025-09 on Macos 15.7.

	JButton addTabButton = new JButton("Add Tab");
	addTabButton.addActionListener(new ActionListener() {
		public void actionPerformed(ActionEvent e) {
			String name = JOptionPane.showInputDialog(this, "Enter tab name:");
			if (name != null && !name.isBlank())
			{
				LaunchTabPanel panel = new LaunchTabPanel();
				tabs.addTab(name, panel);
				tabs.setSelectedComponent(panel);
			}
		}
	});

// addTabButton.addActionListener(e -> {
// String name = JOptionPane.showInputDialog(this, "Enter tab name:");
// if (name != null && !name.isBlank())
// {
// LaunchTabPanel panel = new LaunchTabPanel();
// tabs.addTab(name, panel);
// tabs.setSelectedComponent(panel);
// }
// });

	tb.add(addTabButton);

[ptziegler]

The snippet is sadly doesn't compile because I e.g. don't know what the LaunchTabPanel looks like. Can you perhaps provide a small self-contained snippet where the problem appears?

Can you perhaps also provide a thread dump when the Eclipse freezes? Otherwise it will be very difficult to reason about what exactly goes on, if this happens to be a Mac-specific problem.

[C4J]

demo.java

Apologies - see attached.

[ptziegler]

Thanks! I created a dummy implementation of the LaunchTabPanel that simply extends the JTabbedPane and now I get a similar behavior.

I think there are multiple layers to this problem. When parsing the code, WindowBuilder opens the modal dialog.

Until this dialog is closed again, WindowBuilder (and by extent the Eclipse IDE) is blocked. Can you check whether there's this dialog window? For me it was opened in the background, so I didn't immediately see it.

Once I closed this dialog, the editor got unstuck.

[C4J]

I have recorded my screen, initially I try to open the demo.java file which I attached previously and on Macos at least this just crashes eclipse completely - you cannot interact with it at all.

The app does run and in demo I do see the tabbed pane. For clarity I also show the more complete version afterwards.

[](https://app.screencast.com/CtgyitflddWZ2)

[C4J]

Now that I have identified the problem code, my workaround is fine, so don't worry about it. Did you see the dialog when entering design mode, I would normally have expected only to see that when running the application. Is this a site effect of the lambda expression in the event handler ?

[ptziegler]

Did you see the dialog when entering design mode, I would normally have expected only to see that when running the application.

I did, and that is something that shouldn't happen, as the content of the action handler isn't relevant during design time.

Is this a site effect of the lambda expression in the event handler ?

That's a good catch and it really seems to only happen when using lambda expression, not when using anonymous classes. This at least gives me a hint where to look.

[ptziegler]

@C4J FYI I had a look again at how they are handled by WindowBuilder and outside of some very few exceptions, anonymous classes are always ignored. This handling was never implemented for lambda expressions, which is why the modal dialog in your snippet was opened.

This should be fixed with #1245 and is included in the latest nightly build.

[C4J]

Many thanks, I wish I could resolve code issues as quickly as you.

Most appreciated

Dave

[C4J]

I did not see the dialog - to be honest it wasn’t until I
commented out that code I could see anything. My amended event handler behaved normally with window builder. It seems to be an eccentricity of how ChatGPT likes to create code. I do find its code hard to follow at times - it has its uses for small utility functions but can get itself tied in knots quickly. So by all means look at the cause if it worries you but don’t stress over it for me.

thanks

Dave

[C4J]

This is linked indirectly to the crashing of eclipse today, and possibly unique to eclipse on the mac, so I'm not sure if you can help. Frequently after I have had to terminate Eclipse forcefully rather than a clean shutdown I get odd things happening. For example if I create a new project or just copy/paste an existing one the new project does not show up in the project explorer. Today this happened, however in addition to that I found that WindowBuilder would not render some screens which had not changed in some time and I knew were fine in the past. Eventually I had to create a new eclipse install with plugins, restore a backup of my workspace and merge the latest code changes. A rather cumbersome workaround to what could possibly be an easy fix. I suspect something got corrupted in the .metadata workspace folder, but what ? Is there an easy fix for this ?

[ptziegler]

For example if I create a new project or just copy/paste an existing one the new project does not show up in the project explorer.

I have to admit that I've never seen such a problem after a crash. Sometimes the workspace is out-of-sync and some files are missing, but this is usually fixed after a refresh.

Today this happened, however in addition to that I found that WindowBuilder would not render some screens which had not changed in some time and I knew were fine in the past.

As in: The components view is there but the designer is empty? That's something I've only seen when there are e.g. compilation errors or WindowBuilder was unable to parse the code for some other reasons.

Is there anything suspicious in the error log?

Is there an easy fix for this ?

Maybe not an easy fix, but an easier fix would be to create a new workspace and import the projects via the Import wizard. This way you at the very least keep your local changes.

[C4J]

Thanks, I suspect it's something Mac specific. I have everything working again now. Just need to remember when testing again to use a separate Eclipse and Workspace.