Callback function is not executed anymore after using snapshot or step getting image frames

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Rainer Mautz 2012-6-26

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https://ww2.mathworks.cn/matlabcentral/answers/42083-callback-function-is-not-executed-anymore-after-using-snapshot-or-step-getting-image-frames

采纳的回答： tlawren

I am using a GUI to start and stop my video camera. First I create the videoinput with

vid = videoinput('avtmatlabadaptor64_r2009b',1,'F7M0_Raw8_1032x778');
start(vid);

Everything works fine if I get image data in a loop data with:

image = getdata(vid,1,'single')

But this is extremely slow. So I changed this line into

image = getsnapshot(vid); (or alternatively into image = step(vid); using imaq.VideoDevice)

which both run 10 times faster. My problem is now that my GUI button press functions are not executed anymore when I press a button. The header of this function is: function buttonStop_Callback(hObject, ~, handles) Has anyone an idea how I can fix this problem?

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Image Analyst 2012-6-26

Does the button move at all when you press it? Or change color or get a little dotted line in it?

Rainer Mautz 2012-6-26

yes the button (and others) on my GUI do move when I press them. Only the function behind is not called.

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Answer 1

tlawren 2012-6-26

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What does your stop callback function actually do? Does it set a stop flag variable? When I make data collection GUIs, I typically put my data collection code inside a loop that is designed to run non-stop until a stop flag is set. My stop buttons then have only one purpose and that is to set the stop flag. A rough example of this process is the following.

% pre-collect data stuff
set(handles.StopButton,'UserData', 0);
while (get(handles.StopButton,'UserData') == 0)
   % collect data
end
% post collect stuff

The StopButton function simply sets the UserData field in handles.StopButton to 1.

This may not be the best way to actually collect data in a GUI and it may not be of any use to you (I don't know how getdata and getsnapshot work), but it might be an idea to consider.

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Rainer Mautz 2012-6-26

Not any of all my callback functions would break the while loop until I added a pause(0.01) within the loop. Now it works i.e. the callbacks are called, but it is unclear to me why.

Image Analyst 2012-6-27

I'm not sure why either. All I know is that I've tried to do that before and it doesn't work with buttons, however it does work with checkboxes. So if I need to break out of an intensive, computationally heavy loop I make visible a checkbox that says "Finish now" which the user can click and my loop can check and bail out if it's checked. Then I hide the checkbox until the next time. Making a "Finish Now" button to set a "FinishNow" flag didn't seem to work, I guess because the loop was so intensive it never got around to starting that parallel code execution going. Maybe putting in that pause gave it a chance to catch its breath and do other things, like running that button's callback.

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