Why GUI data is getting deleted after execution of push button command (GUIDE) ?

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Pooja Mehta 2017-7-4

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编辑： doodle 2018-6-4

I am making a GUI in GUIDE, for instrument automation. I am using a push button call "measure" to execute a set of command, but as soon as the command is over all my variables stored in workspace is getting deleted.

I need this variable for my further calculation.

Please help me to figure it out a solution.

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Adam 2017-7-4

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"execute a set of command"

Well, fairly obviously those commands are what is causing this so if you aren't going to show us any specific code there's not a lot we can do.

People often seem to like to include instructions like

clear all
close all force

and other equally silly things in GUIs which can cause unpleasant behaviour.

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Answer 1

Geoff Hayes 2017-7-4

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Pooja - if you are initializing local variables within your callback function like

 function pushbutton1_Callback(hObject, eventdata, handles)
 x = 3;
 y = 4;
 z = 4;
 t = 3*x + 2*y + z;
 % etc.

then so long as the function is being evaluated, the (function) workspace will be populated with the hObject, eventdata, handles, x, y, z, t, etc. variables. When the function completes and so program control leaves the function, then these variables are considered out of scope and so are no longer available.

If you wish to have access to some of these variables (that you have created in your function) then save them to the handles structure so that they the other callbacks can refer to them.

In the above example, suppose I want to save t so that another (different) callback has access to it. I would do

 function pushbutton1_Callback(hObject, eventdata, handles)
 x = 3;
 y = 4;
 z = 4;
 t = 3*x + 2*y + z;
 % do something else with t
 % save it handles
 handles.t = t;
 guidata(hObject, handles);

Note that the guidata is important as it saves the updated handles structure.

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Jan 2017-7-5

@Pooja: Simply try it. You will find out, that t can be a struct array also.

Pooja Mehta 2017-7-17

编辑：Pooja Mehta 2017-7-17

@Geoff What I was missing is to use "guidata(hObject, handles)" command after storing data in particular variables. Thank you for insight.

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Answer 2

Jan 2017-7-4

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all my variables stored in workspace is getting deleted

This leaves to details unclear:

Which workspace
How are the variables deleted and why?

Remember that each function has its own workspace. If you create a variable in the workspace of a callback, leaving the callback will and must delete them. If you need them anywhere else, store the results:

function Buttoncallback(hObject, EventData, handles)
handles = guidata(hObject);  % Safer to get the current value
[X, Y] = YourFunction();
handles.X = X;
handles.Y = Y;
guidata(hObject, handles);  % Store current version in figure again
end

Now all callbacks can access the outputs of the function. You could add an "Export" button, whose callback uses assignin('base', 'X', handles.X) to export the values to the base workspace ("the command window").

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doodle 2018-6-3

编辑：doodle 2018-6-3

Dear Jan,

Thank you for your help above and I apologise if (a) this is an ignorant question based on rank inexperience or (b) more info is required from my side. I am going crazy trying to understand how to do something that ought to be quite simple. Essentially up until now I have happily gathered user data and preferences into the base workspace with inputdlg, and subsequently manipulated that data with whatever analysis is wanted. The drawback is that inputdlg does not lend itself to gathering a lot of data, so you end up with a bunch of dialogue boxes one after another. So I thought to solve this by getting familiar with GUIDE for gathering the user data, then calling my other script(s) as the final step with a pushbutton. One day later I am continually up against a variant of the problem described by Pooja: although I can save the original user input data to the base workspace using assignin as above, most or all subsequent variables that my other script(s) declare, are deleted from the base workspace before they can be used. Maybe something to do with said scripts being treated as part of the pushbutton 'callback' function? (Furthermore, it disturbs me that using assignin in this way is 'not recommended' etc..) I have tried much of the other advice above and elsewhere (e.g. guidata) but it seems I am probably missing something fundamental and thought it may be better to ask in case there is a straightforward alteration I can make to my approach. Is there a straightforward or recommended way to do what I am trying to do - i.e. gather user data in a GUI made using GUIDE, to then be passed to an entirely separate script - or is it just not recommended (and if so, why not / what's the better way?) Questions similar to mine seem to often get the response 'why would you want to do that...?' ... my knee-jerk reaction is 'why would you NOT want to gather user input data and then manipulate it?' Isn't that what most programs aim to do? Sorry if I'm being dim - I hope there is a more appropriate way to do this... happy to provide some example code if it helps.

Pooja Mehta 2018-6-4

编辑：Pooja Mehta 2018-6-4

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@doodle

As @Geoff has explained

for storing the user input data first of all you have to store the data in handles structure.

handles.t = t

Where t is any variable you want to store. And then update GUI data with the command

guidata(hObject, handles)

storing your data in handles is important, then the only guidata command will store your variable and update.

doodle 2018-6-4

编辑：doodle 2018-6-4

Thanks both

Nope, "clear all" not used in the code, and I had already used guidata, although thanks for the suggestions. It did in fact turn out to be a similarly silly mistake, though...

The variables from the later script weren't getting deleted from the base ws [see below] ... they just hadn't been created due to a while-loop condition not being met ... which in turn occurred because of a trivial typo in declaring a variable within the GUI script [embarrassed face]. Always the way...... Sorry to have wasted your time, thanks for the responses!

Note for anyone else working at my fairly basic level:

Technically the variables declared in the other script were being deleted, but only at the very end, because the script had itself been invoked within the pushbutton callback function which clears its variables once finished. [Also this was not the cause of the problem above, as explained.]

For anyone else who finds this behaviour inconvenient, you can call the GUI from the other script rather than vice versa. In that approach, though, you'll then have to make your other script wait for the GUI pushbutton press, documented elsewhere. You'll also have to use 'assignin' (see Jan's answer) to pass the variables to your controlling script (if trying to use guidata as outlined above by various users for the OP's case, the variables will still remain local to the GUI script and so, in this case, can't be called from your controlling script once the GUI script has finished). By contrast, calling the other script from the GUI pushbutton callback doesn't incur these problems, if you don't mind your variables disappearing from the base workspace once everything has finished. Which is probably 'best practice' anyway judging from other threads.... people don't tend to explain "why" this is best practice, but I'm guessing it has to do with the danger of obsolete variables hanging around the workspace to clash with future ones of the same name.

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