MATLAB Answers


Adding dropdown option from GUI in App Designer

Asked by EnergyLights on 11 Jul 2019
Latest activity Commented on by TADA
on 14 Jul 2019
Is there a way to permanently add another option to a dropdown menu without having to go to the code? I will be getting objects periodically that I need to add to the list of options and I wonder if there is a way to add them from the app.
I was thinking about creating a character vector that can be modified through the gui and then make this the input to dropdown.Items. The problem is that from the codeview of my app, that is not a line of code I can modify.
The other option I thought of was activating the "allow users to type in text" function. But this won't remember the options that are typed in for future uses of the dropdown, which is something I would need.
Does anybody know how I can do it?


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1 Answer

Answer by TADA
on 11 Jul 2019
 Accepted Answer

I would put the options in a text file. Then load it during startup


For the sake of this example, let's make it a fully extensible settings struct and not just a list of strings for your drop down options
That can be saved in XML or JSON formats very easily (let's use the leaner JSON format):
That's the content of the settings file ("settings.json") which is saved in the same folder as the app:
it translates to a struct with one field using jsondecode, the same as writing this line of code:
struct('Options', {{'opt1', 'opt2', 'opt3'}})
ans =
struct with fields:
Options: {'opt1' 'opt2' 'opt3'}
I was curious if it would work, so I cooked up this small app:
classdef AppExample < matlab.apps.AppBase
% Properties that correspond to app components
properties (Access = public)
UIFigure matlab.ui.Figure
DropDownLabel matlab.ui.control.Label
DropDown matlab.ui.control.DropDown
Settings struct
SettingsFile = fullfile(fileparts(which('AppExample')), 'settings.json');
% App initialization and construction
methods (Access = private)
% Create UIFigure and components
function createComponents(app)
% load settings
settingsStr = fileread(app.SettingsFile);
app.Settings = jsondecode(settingsStr);
% Create UIFigure
app.UIFigure = uifigure;
app.UIFigure.Position = [100 100 640 480];
app.UIFigure.Name = 'UI Figure';
% Create DropDownLabel
app.DropDownLabel = uilabel(app.UIFigure);
app.DropDownLabel.HorizontalAlignment = 'right';
app.DropDownLabel.Position = [80 306 66 22];
app.DropDownLabel.Text = 'Drop Down';
% Create DropDown
app.DropDown = uidropdown(app.UIFigure);
app.DropDown.Editable = true;
app.DropDown.Position = [161 306 100 22];
% listen to edit event
app.DropDown.ValueChangedFcn = @app.onDropDownValueChanged;
% bind options to drop down
app.DropDown.Items = app.Settings.Options;
function onDropDownValueChanged(app, src, edata)
% if this value changed is due to user editing the field
if edata.Edited
% add new option
% handle value changed normally
function addNewOption(app, value)
% if this option did not exist before, add it to the settings struct and save it
if ~ismember(value, app.Settings.Options)
% add item to settings
app.Settings.Options{numel(app.Settings.Options)+1} = value;
% bind drop down elements
app.DropDown.Items = app.Settings.Options;
% save edited settings
settingsText = jsonencode(app.Settings);
fid = fopen(app.SettingsFile, 'w');
fwrite(fid, settingsText(:));
methods (Access = public)
% Construct app
function app = AppExample
% Create and configure components
% Register the app with App Designer
registerApp(app, app.UIFigure)
if nargout == 0
clear app
% Code that executes before app deletion
function delete(app)
% Delete UIFigure when app is deleted
Now this app would load the options from the settings file at startup, but would also update the file whenever the user edits the options list
This is great! Thanks so much

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