Error running :observer.start() command (macOS)

[thanhchungbtc]

Hi, First of all, thank you for an amazing book. I'm pretty into it.

I have a problem regarding chapter - working with components.
In section 11.2.3 - Visualizing the system, I have run the :observer.start() command, but the window doesn't appear (it actually flashes out).

The terminal fulls of huge cpp errors, like

/src/common/object.cpp(251): assert "classTable->Get(m_className) == NULL" failed in Register(): Class "wxMouseCaptureLostEvent" already in RTTI table - have you used IMPLEMENT_DYNAMIC_CLASS() multiple times or linked some object file twice)?

I am using macOS Big Sur and install elixir through brew.
Is there anything I need to install to make it works?
Thank you.

[sasa1977]

Hi,

I'm mainly on Linux these days, and the one mac I have is not on Big Sur, so I can't give the exact solution. It sounds like this could be caused by the incorrect wx version installed. It seems like this exact issue is reported in the Erlang asdf plugin, with the fix mentioned here. You don't need to actually use asdf for that fix. It would probably be enough to uninstall Elixir and Erlang, then install the correct wxmac according to the instructions, and then reinstall Elixir and Erlang with brew.

You could also try the suggestion in this Elixir forum thread.

As an aside, I recommend using asdf instead of brew. I find it very useful for switching between projects which use different Erlang/Elixir versions. You'll need asdf-erlang and asdf-elixir plugins. I also use it to manage nodejs, for Phoenix-based systems. Note however, that asdf will probably not fix this issue, so I suggest taking care of that first (by installing the correct wxmac).