writeVideo function not accessible from appdesign (only from script)

Using MATLAB 2018a, I build an appdesign interface that should create a video file.

When I execute the app, the line:

 writeVideo(vid,frame);

throws the error: Undefined function or variable 'writeVideo'. However, the very same code, executed outside appdesign (in a script) runs perfectly. I also verified whether writeVideo is accessible from the app by writing

 which writeVideo
 writeVideo(vid,frame);

which gave me the correct location of the writeVideo method:

/Applications/MATLAB_R2018a.app/toolbox/matlab/audiovideo/@VideoWriter/VideoWriter.m  % VideoWriter method

However, the next line still throws the aforementioned error. I cannot get my head around how this could be logically possible.

Many thanks for any ideas!

[Walter Roberson]

At the point that the problem occurs, what shows up for

class(vid)

?

[Jannis]

It shows

VideoWriter

for both scenarios. That doesn't make it easier, I guess?

[Walter Roberson]

In cases like these, I would erase the writeVideo word and type it back in again, just in case I was having difficulty seeing a spelling mistake.

[Greg]

Very odd. I have no troubles. After what Walter suggested, does methods(vid) inside the app code list writeVideo as an option?

[Walter Roberson]

One thing I would wonder about is whether the MATLAB path is somehow getting clobbered.

[Jannis]

I could resolve the problem. I had an error further down in my code where I was iterating over a 2D cell of vids, so as: writeVideo(vid_cell{2,1},frame). However what still confuses me that this mistake was done after the line that threw the error, in both code and execution time. I never had that before in MATLAB, is it just coincidence or may it be due to some compiling in appdesign?

The methods(vid) test gave me the right result, so as which writeVideo did. Interestingly open writeVideo threw an error (I guess that's expected since it is only defined inside VideoWriter?)