Add this to the value changed callback, adjust the name of your field.
if length(app.EditField.Value) <= 20
Text = app.EditField.Value; % If you will use the text
else
% app.EditField.Value = ''; % you can clear out the text if needed
f = uifigure;
Error_Msg = "Error message"
Error_Title = "Error title";
uialert(f, Error_Msg, Error_Title,'CloseFcn',@(h,e) close(f));
end
It takes a little bit of time to display the message, if that is an issue, then you can use tooltip, I have no example with tooltip.
Above portion of code creates a new figure which takes a bit of time. Here's a better solution with help from Adam.
if length(app.EditField.Value) <= 20
Text = app.EditField.Value; % If you will use the text
else
% app.EditField.Value = ''; % you can clear out the text if needed
f = app.UIFigure; % f is handle to your app UI figure
Error_Msg = "Error message"
Error_Title = "Error title";
uialert(f, Error_Msg, Error_Title);
end
