how to interrogate handle

I am working on a GUI and associated program written by someone else. It would be useful if, while executing the GUI, I can monitor the evolution of variables used in the program in real time from the interactive window. I don't know how to access them though. For example for something like handle.data.val, how can I see its value by commands issued in the interactive window?

Answer 1

[Walter Roberson]

openvar('handle')

In the command window, provided that handle is in scope, you can use

handle.data.val

Note: if it is a GUI, then it is more likely that the variable is named handles and that data is the handle of a uicontrol, and that you want to look at its Value or String. If you are using up to R2014a you would use

get(handles.data, 'Value')
get(handles.data, 'String')

From R2014b onward you can also use

handles.data.Value
handles.data.String

[Yu-Chiu Chao]

Hi Walter, Thanks a lot for this input! I guess for my lack of understanding of the workings of matlab GUI, I still can't quite get it. I tried openvar('handles'). The variable editor opened but said "handles does not exist".

What I am trying to do is the following, taking the simple_gui example given in the matlab tutorial if you are familiar with it: I launch the simple_gui GUI which plots 3D and contour plots. The graph type and data etc. are defined internally in locations labeled as structure attributes of the global object "handles", such as handles.current_data. I would like to see the explicit form of this handles.current_data in the interactive window as the GUI is active.

I know some of these may be graphics objects that cannot be easily accessed, but some of them are simply 1/0 logicals. If I simply type handles.current_data, of course I get an error. But is there a way I can see what the values of this is? Thanks a lot!

YC

[Walter Roberson]

When you are building a GUI using GUIDE, handles is a parameter to each function, and it only exists until the function exits, so unless you put in a breakpoint in the routine of interest, you cannot truly look at it.

handles is not a global variable: it is something that is built at run-time just as each routine is called.

However, the way that GUIDE works with handles is that for each GUI, there is a "master copy" of the handles structure. At any time the code can request a copy of what is currently stored in the "master copy". That becomes a local copy that lives in the workspace of the one function, and the local copy will be destroyed when the function returns. You can make any number of changes to the local copy without there being any change to the master copy.

However, inside a function, if you have your local structure named handles, then if you happen to call

guidata(hObject, handles);         %writes to master copy

or equivalent, then that local version will overwrite the "master copy". That will not affect any local copies that might happen to still exist: if you have a local copy of handles and you have reason to suspect that some other routine might have changed the master copy while you are still running, then you need to ask for an updated local copy of the master copy,

handles = guidata(hObject);    %fetches from master copy

You can do that fetching of the master copy when you are at the MATLAB command line, but for hObject you would substitute the figure number of the GUI:

handles = guidata(gcf);

[Yu-Chiu Chao]

Hi Walter, Thanks a lot! This is very useful!

YC