Help with GUI callback - existence condition

Hello! I'm working on a GUI in Matlab, and I have a simple question. I have two 'Push button' commands, let's say 'Button1' and 'Button2', and two 'Edit text' commands. The two 'Edit text' commands are tagged as 'a' and 'b'. Let's suppose I write two numbers in these two Edit text commands, and by pressing 'Button 1' I save them in a handle structure inside the callback function of 'Button1' (e.g. a = str2num (get(handles.a,'String'));b = str2num (get(handles.b,'String')); handles.num1=a; handles.num2 = b). Then, by pressing 'Button 2', inside its callback function I recall these two numbers (num1=handles.num1; num2=handles.num2 - e.g. num1 = 98 and num2 = 21) and do an operation between them.

Now, let's suppose I want to press directly 'Button 2' to perform the same operation between num1 and num2 but without writing them in the edit text commands: of course the callback function of 'Button 2' will not recognize any 'num1' and 'num2', because I don't save them in any handle structure before. What I want to do is to write this condition in the 'Button 2' callback: " If 'num1' and 'num2' don't exist - i.e. the condition satisfied by pressing directly 'Button 2' - then set num1 = 100 and num2 = 20 "; then the rest of the code will be the same. How can I translate this into a code inside the 'Button 2' callback function? Thank you very much.

Answer 1

[Adam]

isfield( handles, 'num1' )

will tell you if num1 exists as a field in your handles structure.

It isn't necessarily the way I would suggest going about what you are trying to do, but if I understand your question correctly it will achieve what you want, though only on the first press of button 2 before button 1. If button 1 is still creating these fields then they will exist for the lifetime of your GUI on handles after their first creation unless you explicitly remove them

[aurc89]

Thanks!

Answer 2

[Ben11]

You can check for the non-existence of a variable using this line:

if ~exist('a','var')

% Code

else

% code

end

[aurc89]

And what is the syntax for a condition on 'a' and 'b' at the same time ? Is it correct like this:

if ~exist ('a','var' && 'b','var') ?

Thanks!

[Ben11]

Nope you would have to use 2 calls to ~exist:

if ~exist('a','var') && ~exist('b','var')

Actually Adam's answer is more appropriate for the handles structure; but it's good to know this alternative :)

[aurc89]

Thank you so much :)

[Ben11]

you're welcome! If my answer helped you can give it a vote up :) Glad to help!