About updating value of handles whithin loop

function pushbutton4_Callback(hObject, eventdata, handles)
handles.st=1
guidata(hObject, handles);

this is the code to stop video with push button, to start the video:

function pushbutton2_Callback(hObject, eventdata, handles)
info=imaqhwinfo('winvideo')
vid=videoinput('winvideo',1)
set(vid, 'FramesPerTrigger', Inf);
set(vid, 'ReturnedColorspace', 'rgb')
vid.FrameGrabInterval = 50;
start(vid)
sto=0;
while(sto==0)
    if(vid.FramesAcquired>=10)
        break;
    end
data = getsnapshot(vid);
axes(handles.axes1)
imshow(data)
guidata(hObject, handles);
drawnow;
pause(2);
sto=handles.st
end

the problem is when i press stop button and update st to 1 it take sto as well as st 0 always

[Stephen23]

@Devendra Singh: I formatted your code correctly for you, but in future you can do it yourself by selecting the code text and then clicking the {} Code button. It also helps if you do not have empty lines as every alternate line of the code.

Answer 1

[Dennie]

Matlab GUI's use callbacks to handle the button interrupts. However, the callbacks cannot interrupt each other. Matlab use a sequential method for this, meaning that when you press two buttons in the GUI it first finishes the first callback and afterwards the second. This is the reason that your value is not being updated during the while loop.

A trick that you could try to break the loop is using a toggle stop button and read out that value in the loop

while(sto==0)
   if(vid.FramesAcquired>=10)
       break;
   end
data = getsnapshot(vid);
axes(handles.axes1)
imshow(data)
guidata(hObject, handles);
drawnow;
pause(2);

sto=get(handles.stopbutton,'Value');

end

This will force matlab to read out the current value of the button and since you use a toggle button, you don't have to worry about timing.

[Devendra Singh]

Dennie Sir,could you please suggest what to write in toggle button callbacks .