MATLAB Answers


How do I pass a value out of a GUI when button is pressed? The value must be available to another m file

Asked by Brian
on 26 May 2013


I am making a GUI which adds rows to a matrix in one part. I want the matrix to be available to another m-file when I press another button (export). I've been looking at this for two weeks and can't figure it out. What is the syntax to make this matrix available to another function? eg x = function (y, exported_matrix). The normal [export_matrix] =Callback_pushbutton(....) doesn't work for GUI's. Can someone explain this? Sorry, this is probably basic but I can't see by any examples how this would work with my own GUI.





No products are associated with this question.

3 Answers

Answer by Brian
on 25 Jun 2013
 Accepted answer

For reference to anyone with the same problem: Use global. It may or not be bad programming practivce but it works. global has to be stated in BOTH m files.


m-file 1

global BND_CDN

in m-file 2:

global BND_CDN
a = BND_CDN etc.

  1 Comment

You had said "I have tried global, ..., I have been at this for three days, I'm not getting it. " I guess you eventually got it right.

Answer by Image Analyst
on 26 May 2013


"assignin(test_3, 'BND_CDN', BND_CDN)" should fail, because "test_3" will most likely not reply one of the two allowed strings 'base' or 'caller' - look into the documentation to find out more: doc assignin.

Assigning variables remotely and magically using ASSIGNIN or EVALIN increases the complexity of a program and decreases the processing speed. So it is recommended to avoid it strictly, especially for beginners. And to be absolutely clear in this point: Don't do this!

I'll try to stay away from that, as I am a beginner. I'll try using handles. Cheers

Thanks for your time, I couldn't get it to work. I needed a simple answer, global did it, I didn't understand that global had to be in both files

Answer by Jan Simon
on 21 Jun 2013
Edited by Jan Simon
on 21 Jun 2013

Assume your GUI has the tag-property 'MyGUI' (a more meaningful tag is recommended...). Then the store the matrix in the handles struct inside the GUI:

handles.matrix = rand(10, 10);  % Or how ever you define the elements
guidata(hObject, handles);  % 1st argument: handle of the current object

Now obtain the matrix from your external M-file:

function theExternalFunction
guiHandle = findobj(allchild(0), 'flat', 'tag', 'MyGUI');
guiHandles = guidata(guiHandle);
matrix = guiHandles.matrix;

guidata() is a wrapper for setappdata() and getappdata(). Some exceptions should be caught by tests, e.g. if the guiHandle cannot be found because the GUI has been closed before, etc.


Thanks for your help. I still can't work it though. The output when I press the button in the GUI seems to be working, the output with colons removed is:

handles = 
        figure1: 173.0012
    pushbutton1: 174.0012
         output: 173.0012
            bnd: [100x5 double]

As testing, I copied your code and slightly changed it:

function theExternalFunction
guiHandle = findobj(allchild(0), 'flat', 'tag', 'test_2')
guiHandles = guidata(guiHandle)
BND_CDN = guiHandles.BND_CDN

The output in the command window is then

 guiHandle =
   Empty matrix: 0-by-1
 Error using guidata (line 89)
H must be the handle to a figure or figure descendent.
 Error in test_theExternalFunction (line 3)
guiHandles = guidata(guiHandle)

Should the guiHandle matrix be populated? Do you know what the problem is? Thanks again

Thanks for your time, I couldn't get it to work. I needed a simple answer, global did it, I didn't understand that global had to be in both files

Join the 15-year community celebration.

Play games and win prizes!

Learn more
Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

MATLAB Academy

New to MATLAB?

Learn MATLAB today!