matlab: gui and global variables

Question

I'm having several functions (defined in separate files) within a Callback in my GUI, like that:

function myFunction_Callback(hObject, eventdata, handles)
[output] = function1(input);
[output] = function2(input);
[output] = function3(input);
guidata(hObject, handles);

Now, lets say I'm defining function1, and I want to store a local variable in handles. When I do like that:

[output] = function1(input)
localVariable = [1 2 3];
handles.myVariable = localVariable;

handles.myVariable 'disappears' from handles once the function1 is completed. How to make it 'stay' in handles? Do I have to define it as an output and later store in handles like that:

[output, localVariable] = function1(input)
...
localVariable = [1 2 3];

and later

function myFunction_Callback(hObject, eventdata, handles)
[output, handles.myVariable] = function1(input);
[output] = function2(input);
[output] = function3(input);
guidata(hObject, handles);

?? I know this question sounds super stupid and might be unclear, but forgive me, I'm very confused with GUI and handles newbie :) thanks!

score 1 · Accepted Answer · answered Nov 05 '12 at 06:50

Yes, your general approach is OK, although there are a few things:

handles typically refers to a data structure that contains handles to objects. Adding other types of data to this is valid but not advisable because it's simply confusing.
the brackets around single outputs of functions are not necessary. Granted, it's a matter of taste and coding style, but it's something I'd recommend against; use brackets only to group things that belong together.
Does your input contain handles somewhere? Similarly, do the function outputs contain a modified version of handles? If no function modifies handles, there's of course no need to re-save it every time the callback is called...

So, in summary, do it something like this:

function myFunction_Callback(hObject, eventdata, handles)
    ...
    output = func1(input);  
    output = func2(output);  
    output = func3(output);
    ...
    guidata(hObject, output);  % <-- NOTE: output contains handles


function output = func1(input)
    ...
    output.handles = input.handles;
    ...
    output.localVar = [1 2 3];
    ...

score 1 · Answer 2 · edited May 23 '17 at 12:12

Passing data around such functions can be quite a pain.

I found it very helpful to apply object oriented programming for these causes. Especially defining your class as classdef myclass < handles. Using these you can do all kinds of cool stuff easily - such as transfering data between unrelated figures.

It is helpful to implement a singleton pattern instead of a global. I also gave an answer here showing an observer pattern.

matlab: gui and global variables

2 Answers2