How to pass/share data between GUIs?

I am trying to make a GUI that:

1stGUI: enter the number of tasks to run, then click "next" button to open another GUI to run the task.

% --- Executes on button press in Next_Button.
function Next_Button_Callback(hObject, eventdata, handles)
% hObject    handle to Next_Button (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
if get(handles.Num_Task, 'Value') ~= 0
    GUI_2
else
    errordlg('Input cannot be zero.','Task Num. 0')
end

2ndGUI: run the task for the number of times entered in the 1stGUI.

So the question is, how do I access the "number of tasks" from the 1stGUI within the 2ndGUI, and also, 2ndGUI will run "number of tasks" times, and creates a matrix as the row number is "number of tasks" to store the data.

I read about "guidata", but did not get it to work.

Answer 1

[Geoff Hayes]

Peng - please see https://www.mathworks.com/matlabcentral/answers/146215-pass-data-between-gui-s for an example of sharing data between GUIs. Your second GUI will need to be able to find the first GUI (via its tag/name) and then get the handles object for that first GUI.

In the OpenFcn of your second GUI, you could add code similar to

 % get the handle of Gui1
 h = findobj('Tag','Gui1');
 % if exists (not empty)
 if ~isempty(h)
    % get handles and other user-defined data associated to Gui1
    handlesGui1 = guidata(h);
    % get the number of tasks
    numberOfTasks = get(handlesGui1.Num_Task, 'Value')
 end

[Peng Zhao]

I tried to put the following lines in my OpeningFcn of 2ndGUI:

 % get the handle of GPEC_Task_Generator
 h = findobj('Tag','GPEC_Task_Generator');
 % if exists (not empty)
 if ~isempty(h)
    % get handles and other user-defined data associated to GPEC_Task_Generator
    handles_GPEC_Task_Generator = guidata(h);
    % get the number of tasks
    NumOfTasks = get(handles_GPEC_Task_Generator.Num_Task, 'Value')
 end

However, seems like <if ~isempty(h)> this line never met.

Am I missing anything to add in 1stGUI?

[Geoff Hayes]

In the Property Inspector for GPEC_Task_Generator, set the HandleVisibility property to on, and confirm that the Tag property is set to GPEC_Task_Generator.

[Peng Zhao]

Thank you, it is now working!