How to specify when to return output of the function

Question

Say I have the following function:

function result=myfun(varargin)    
result=[];    
myFig=figure();    
B1=uicontrol(myFig,'Style','pushbutton','String','done','Callback',{@done_Callback});    

    function done_Callback(varargin)  
        result =10;
        delete(mainFig);
    end
end

I am trying to only return output after the button callback is executed. Right now it returns an empty variable right away. I know how to do this in guide GUIs but all of my project is written without guide. I am assuming I need uiwait somewhere, but not sure where.

A. Donda · Accepted Answer · 2013-11-18 19:15:19Z

2

The function uicontrol only generates the button, it doesn't wait for it to be pressed. Otherwise, a full GUI with several elements would not be possible – you couldn't insert another element before the first hadn't been activated, and afterwards the first one could not be activated any longer. For this reason, GUI callbacks are executed in another thread than the main Matlab program, namely in the "event queue".

If you want your program to wait until the button is pressed, you have to program this explicitly:

function result=myfun(varargin)    
result=[];    
myFig=figure();    
B1=uicontrol(myFig,'Style','pushbutton','String','done','Callback',{@done_Callback});    
while isempty(result)
    drawnow
end

    function done_Callback(varargin)  
        result =10;
        fprintf('hi\n')
        delete(myFig);
    end
end

The drawnow is there to tell Matlab it should allocate execution time to the event queue, which is not normally done when Matlab is busy, e.g. with running a while loop.

For (slightly) more information, have a look at How Does a GUI Work? and drawnow.

edited Nov 18, 2013 at 19:15

answered Nov 18, 2013 at 19:00

A. Donda

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2 Comments

user2908313 Over a year ago

Thank you very much. This does exactly what I wanted.

A. Donda Over a year ago

You're welcome. :) I just edited the answer once more, maybe you find the additional information interesting.

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