MATLAB: What does guidata do

callbackcallbackfunctioncallbacksguiguidataguideMATLAB

I'm using an older version of Matlab – R2009b. In my callbacks, I often call something like:

set(handles.tag1,'Value',5)
guidata(hObject,handles); 
% ^This seems unnecessary because I'm accessing the handle to tag1 directly

According to current documentation, I should follow this up with guidata, but I haven't identified a place where this actually matters. I think I'm bypassing the need to call guidata because I'm setting the handle directly.

I think this wouldn't be the case in a later version of matlab, in which handles is a complete structure. In the newest version of matlab I'd write this:

handles.tag1.Value = 5;
guidata(hObject,handles); 
% ^Now necessary because the handles structure is contained in this workspace

Now, the changed value to handles.tag1.Value only affects the current workspace (inside my callback) unless I either make handles an output of the callback or call guidata. I'm new to making GUIs with guide so I just want to make sure I understand these functions correctly. Can someone confirm my understanding is correct, or explain what's really going on?

Thank you.

Best Answer

It actually works as you described it

Guidata stores a struct to your GUI, or loads a saved struct. If you make changes you need to save them. Neither of the syntaxes you describe require saving, because you are modifying object properties, not the struct contents.

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I commented out the uiwait in your above code as I don't think that it was in the correct place (before the call to guidata) and am not sure what it's intent is.

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