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Problem with value property of uidropdown

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Hi,
I'm using a uidropdown control with the Items and ItemsData properties set within the method startupFcn of my app. I'm using the following simple code to specify the items of the dropdown control along with numeric IDs:
app.MethodDropDown.Items = Methods.TYPES(:, 1);
app.MethodDropDown.ItemsData = [Methods.TYPES{:, 2}];
Methods.TYPES is a cell-array in class Methods with the first column containing character arrays (i.e. the names for the method types) and the second column contains numeric ID values for the method types.
When retrieving the value of the selected item I observe a different behavior between different MATLAB versions. Up to 2022b the Value property returns the numeric value of the selected item as specified in ItemsData. However, starting with 2023a, a string (i.e. in my case a character array) is returned.
Am I doing something wrong? I suspect that something changed between 2022b and 2023a but I can't find anything about such a change in the changelog of MATLAB. Moreover, the documentation of 2023a still states that my code seems to be correct.
Best,
Michael

Answers (1)

Pavan Sahith
Pavan Sahith on 30 Jul 2024
Edited: Pavan Sahith on 30 Jul 2024
Hello Michael,
It appears that you're encountering an issue with the 'uidropdown' control in MATLAB R2023a,
I use the same version and attempted to reproduce the problem using a simplified example. Here are the steps I followed and the code that worked correctly for me, returning the numerical ID as expected:
1.Added the startupFcn:
  • In the Component Browser, click on the app node.
  • In the right-hand pane, scroll down to the "Callbacks" section and click on "Add StartupFcn". This will create a new function called startupFcn.
function startupFcn(app)
% Define the Methods.TYPES cell array
Methods.TYPES = {
'Method1', 1;
'Method2', 2;
'Method3', 3;
};
% Set the items and items data for the dropdown
app.MethodDropDown.Items = Methods.TYPES(:, 1);
app.MethodDropDown.ItemsData = [Methods.TYPES{:, 2}];
end
2. I inserted a button to retrive the value and added a callback to it.
% Button pushed function: RetrieveValueButton
function RetrieveValueButtonPushed(app, event)
selectedValue = app.MethodDropDown.Value;
% Display the selected value
disp(selectedValue);
end
you can refer to this MathWorks documentation to know more : uidropdown
  5 Comments
Pavan Sahith
Pavan Sahith on 1 Aug 2024
Edited: Pavan Sahith on 1 Aug 2024
Good to know ,
yeah the issue is reproducible with the code provided.
I also noticed that in MATLAB R2023b, there's an update that allows us to access the index of the component value in the list of items using the ValueIndex property.
I believe this might be helpful in the meantime
Michael Liedlgruber
Michael Liedlgruber on 2 Aug 2024
Yes, the ValueIndex could be a solution to not run into the problem. But for that I would have to rewrite a lot of my code which I simply do not want.
I also have a final update from Mathworks: they confirmed that the problem is caused by a bug in copyobj. An enhancement request has already been filed and it should get fixed in upcoming updates. A workaround from Mathworks is to set the ItemsData property to empty after using copyobj and then set the ItemsData property again to the values needed:
h = uidropdown(uifigure,'Items',{'A' 'B' 'C'}, 'ItemsData', [1:3], 'Value', 3)
% copy into new uifigure -> Value is set to Item instead of ItemData element
hc = copyobj(h,uifigure,'legacy')
% workaround: set ItemsData to empty and back to default
hc.ItemsData = [];
hc.ItemsData = [1, 2, 3]
But this is not possible in my case since the apps with the different settings pages are loaded dynamically. And the class, loading the settings pages on demand, does not know anything about the ItemsData properties needed.
So, I guess that I will simply store the ItemsData values to the UserData property. And then I will use a wrapper function for copyobj, which searches through all children of the destination panel with the copied objects to find uidropdown controls and set the UserData values to ItemsData, if set.
Seems a bit cleaner to me.
Best,
Michae

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