How to avoid using eval in this case?

Question

xiaojuezi 2021-12-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1606130-how-to-avoid-using-eval-in-this-case

评论： Matt J 2021-12-8

Hi, I read in multiple threads that the usage of the function eval should be avoided as much as possible. But in the following case I couldn't find a neater way to do so. I have a uicontrol function, and I have several buttons that will set different variables in a similar way. The code is somewhat like below:

w = -1;
h = -1;
editW = uicontrol('Style','edit');
buttonW = uicontrol('Style','pushbutton');
editH = uicontrol('Style','edit');
buttonH = uicontrol('Style','pushbutton');

In total I have more than 5 pushbuttons, each set a specific variable to what is written in the associated edit field. One way to write the callback functions is:

buttonW.Callback = @setW;
buttonH.Callback = @setH;
function setW(hObject,eventData)
    w = str2double(editW.String);
end
function setH(hObject,eventData)
   h = str2double(editH.String);
end

In this way, I will have to write more than 5 callback functions, which they are simply doing very similar things, making the code look very redundant. So I was thinking using the eval function:

buttonW.Callback = {@setVariable,'w'};
buttonH.Callback = {@setVariable,'h'};
function setVariable(hObject,eventData,input)
    % Grab the associated edit field
    edit = eval(['edit',upper(input)]);
    x = str2double(edit.String);
    eval([input '= x']);
end

In this way, I only need to define the function once. Is there other way to somewhat achieve the same effect without using the eval function?

Thank you very much!

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Walter Roberson 2021-12-8

在 MATLAB Online 中打开

function setW(hObject,eventData)
    w = str2double(editW.String);
end

I am not clear as to what the purpose is of setting a local variable that is going to be immediately thrown away.

function SetVar(hObject, eventData)
   value = str2double(hObject.String);
end

xiaojuezi 2021-12-8

Hi, the button is a "OK" button, when a user enters something in the edit field, the variable is only set when they press the button. The variables "w","h"......are also used in global scope. So if there are 6 variables, then there are 6 edit fields and 6 OK buttons, and each button should only control an associated edit field and variable.

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Answer 1

Matt J 2021-12-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1606130-how-to-avoid-using-eval-in-this-case#answer_850615

编辑：Matt J 2021-12-8

在 MATLAB Online 中打开

Store the numeric result to the UserData property of the button, instead of to individual variables.

edit(1) = uicontrol('Style','edit');
button(1) = uicontrol('Style','pushbutton');
edit(2)= uicontrol('Style','edit');
button(2) = uicontrol('Style','pushbutton');
input.edits=edit;
input.buttons=button;
[button.Callback]=deal({@setVariable,input})
function setVariable(hObject,eventData,input)
    idx=arrayfun(@(a,b) isequal(a,b), hObject, input.buttons);
    
    hObject.UserData = str2double(input.edits(idx).String);
 
end

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xiaojuezi 2021-12-8

Thank you very much for your answer! I added this button function because users may be changing their input at any time, and the stored values might also be used at different places in the program. So I only want to change the stored values unless users have confirmed what they've entered.