Passing data using handles in GUI in functions with for loops?

I can't quite figure out what I am doing wrong here. My function is long and has a number of variables that are working properly, so I focused on the important bits below. Upon GUI initialization, I create an array of zeros that I look to change values in later:

handles.ActiveCheck = zeros(1,64);
guidata(hObject,handles);

I then have a callback function based on a togglebutton that functions as a while loop while the program is running; this loop checks if a given value in the previously defined ActiveCheck is 1:

    while true
        for channel = [2,5,7]
            if ActiveCheck(channel) = 1
               plot(x)
            end
        end
    end

Finally, I have a callback function for a checkbox (I have many checkboxes) that simply changes a given value in the array to 1:

handles.ActiveCheck(2) = 1
guidata(hObject,handles)

The problem I am running into is that while the checkbox callback is successfully changing the value to 1 at the given position, this change does not hold and is not seen by the looping while function.

[Daniel Henry]

Nick, did you ever figure out a solution to this problem? I'm running into a similar issue right now.

Answer 1

[Prateekshya]

Hello Nick,

The issue you are encountering is likely due to the scope and persistence of the handles structure within your GUI callbacks. In MATLAB GUIs, the handles structure is used to store and share data between different callbacks. However, if you do not update and retrieve the handles structure properly, changes made in one callback may not be visible to others.

Here is a breakdown of what you should do to ensure that changes to handles.ActiveCheck persist and are accessible across different callbacks:

• Ensure Proper Use of guidata: After modifying handles, always use guidata(hObject, handles) to save the updated handles structure. This makes the changes available to other callbacks.
• Retrieve handles in Each Callback: At the start of each callback, retrieve the latest version of handles using handles = guidata(hObject);.
• Update handles in the While Loop: Ensure that the while loop callback retrieves the latest handles structure. Since this loop is continuous, you may need to periodically retrieve handles inside the loop to check for updates.
• Use Proper Logical Comparison: Ensure that you use == for logical comparison instead of = (which is for assignment).
• Avoid Busy Loops: The while true loop can make your GUI unresponsive. Consider using pause or a timer object to periodically execute code without blocking the GUI.
• Debugging: Use disp or fprintf statements to print values and ensure that changes to handles are being made and retrieved as expected.
• Concurrency: If you have multiple callbacks modifying handles, ensure they are properly synchronized to avoid race conditions.

I hope this helps!