How to get values from workspace to GUI with 'evalin'? error occuring

Question

John 2015-9-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/240643-how-to-get-values-from-workspace-to-gui-with-evalin-error-occuring

编辑： Stephen23 2015-9-7

Hi,

i am just about creating my first complex GUI in MATLAB and i have one question plz. I created a GUI_1 that with the help of a push button starts a GUI_2. In GUI_2 the user can give some input values.

those input values (here for example the variable 'a') are given to the workspace with:

assignin('base', 'var1', a);

This works fine!

>> who
Your variables are:
var1  var2

Now i want to have access to this variable that i named 'var1'. This access should be in a Callback from a push Button in GUI_1. Pressing this Push Button shall load the variables from workspace and start the main script.

I use the function 'evalin' for this:

function run__Callback(hObject, eventdata, handles)
% hObject    handle to run_ (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
temp1=evalin('base',var1)

Pushing the Push Button results in that error:

Undefined function or variable 'var1'.
Error in Try1>run__Callback (line 259)
temp1=eval('base',var1)
Error in gui_mainfcn (line 96)
        feval(varargin{:});
Error in Try1 (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)Try1('run__Callback',hObject,eventdata,guidata(hObject))
Error while evaluating uicontrol Callback

How can it be? i checked the variables that are in the workspace and i saw that

function run__Callback(hObject, eventdata, handles)
  % hObject    handle to run_ (see GCBO)
  % eventdata  reserved - to be defined in a future version of MATLAB
  % handles    structure with handles and user data (see GUIDATA)
    who
    %temp1=evalin('base',var1)

results in

Your variables are:
eventdata  hObject    handles

so why arent there var1 and var2 in the workspace anymore??? why are they lost...?

Best regards, John

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Answer 1

Geoff Hayes 2015-9-7

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/240643-how-to-get-values-from-workspace-to-gui-with-evalin-error-occuring#answer_191550

编辑：Geoff Hayes 2015-9-7

在 MATLAB Online 中打开

John - in your line of code

temp1=evalin('base',var1)

the var1 should be wrapped in single quotes since the second input is an expression (see evalin for details). Try instead

temp1=evalin('base','var1')

Note that there is an alternative to using (polluting) the base workspace to share data between GUIs. See http://www.mathworks.com/matlabcentral/answers/146215-pass-data-between-gui-s which describes a couple of ways on how you can accomplish this.

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John 2015-9-7

Thank you very much Geoff!! it works fine now! nevertheless i may take a look at the other opportunity and follow your link!

Thanks!!!!!:)

Stephen23 2015-9-7

编辑：Stephen23 2015-9-7

@John: actually evaluating variables into existence is the worst way of doing this. If you want to learn how to write faster, more robust and better code then it is worth learning how to pass variables properly between callbacks and workspaces.

Although using eval and evalin are very popular with beginners, there is a reason why MATLAB advises to avoid them: they are slow and buggy. Learn better ways to program.

http://www.mathworks.com/matlabcentral/answers/14857-where-do-people-learn-bad-programming-habits-i-e-goto-global-and-eval

http://www.mathworks.com/matlabcentral/answers/33411-eval-is-giving-wrong-results

http://www.mathworks.com/matlabcentral/answers/26225-how-to-check-if-eval-changes-values-of-any-local-variables

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