MATLAB: Do the callbacks only work if triggered in the order they are defined

callbackguideMATLAB

I have defined my callbacks like so:

set(handle,'callback',{@foo, handles})
function foo(hObject, event_data,handles)
...
set(handle, callback',{@bar, handles})
function bar(hObject, event_data,handles)
...

Best Answer

This issue is because each callback is being set the end of the body of the previous callback. Thus, they will not be set unless the previous callback is executed. The solution is to move all the 'set' function calls to above all the callback definitions:

set(handle,'callback',{@foo, handles})
set(handle,'callback',{@bar, handles})
function foo(hObject, event_data,handles)
  ...
end
function bar(hObject, event_data,handles)
  ...
end

Related Solutions

MATLAB: OpeningFcn not saving handles

This is occurring because in your OpeningFcn, you are calling "guidata" after calling your callback function.

guidata can manage only one variable at any time. Subsequent calls to guidata(object_handle,data) overwrite the previously stored data.

For this reason, your call to "guidata" after your callback function is overwriting the new handles values. Instead, call "guidata" and then call your callback function.

function test_OpeningFcn(hObject, eventdata, handles, varargin)
handles.output = hObject;
guidata(hObject, handles);
pushbutton1_Callback(hObject, eventdata, handles) %call after guidata so not overwritten

MATLAB: How to set up a uicontrol callback to interrupt a routine

In order to address this issue it is important to understand how MATLAB handles events. MATLAB does not automatically detect events as they occur. When events occur, they are placed into the 'event queue'. MATLAB stops the execution of a routine to look at the event queue only when one of a few commands are executed:

drawnow

figure (including gcf and gca)

getframe

waitfor

pause

'drawnow' is usually the command used to access the queue, since 'figure' has (probably undesirable) side effects (i.e. creating a figure), and 'getframe' takes longer to execute.

If the current process (when the event queue is examined) was issued from the command line, the process is suspended and the event queue is evaluated (i.e. callbacks occur). If the current process is itself a callback, the 'interruptible' property of the callback is consulted in order to decide whether or not it will be suspended in favor of event queue processing.

Here is a short example to illustrate these principles:

%%Example program -- can be run as a MATLAB script
h = uicontrol(gcf, 'style', 'pushbutton', ...
     'callback', 'setappdata(gcf, ''run'', 0)');
flag = 1;
setappdata(gcf, 'run', flag);
disp('Entering loop');
n = 0;
while flag
     n = n+1;
     set(h,'string',num2str(n))
     flag = getappdata(gcf, 'run');
     drawnow
end
disp('Done with loop');

Best Answer

Related Solutions

MATLAB: OpeningFcn not saving handles

MATLAB: How to set up a uicontrol callback to interrupt a routine

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