How to use varargout in a GUI

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Simon Aldworth 2018-10-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/425668-how-to-use-varargout-in-a-gui

评论： Walter Roberson 2018-10-24

Hi,

There is clearly something I don't understand about getting data from a gui into my main code. For the purposes of an example, I created a gui using GUIDE that contained a single edit box that I left exactly as it was created. In the automatically generated code are lines in OpeningFcn that define handles.output and update guidata:

function dummy_OpeningFcn(hObject, eventdata, handles, varargin)
% Choose default command line output for dummy
handles.output = hObject;
% Update handles structure
guidata(hObject, handles);

Then, in the OutputFcn, varargout{1} is set equal to handles.output:

function varargout = dummy_OutputFcn(hObject, eventdata, handles)
% Get default command line output from handles structure
varargout{1} = handles.output;

When I run the gui I don't see any variables in the main workspace. What is varargout for if not to pass data to the main workspace? Is there something missing from the automatically generated code that I need to insert so I can access handles.output in the main workspace?

Thanks,

Simon.

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Walter Roberson 2018-10-23

在 MATLAB Online 中打开

To emphasize:

When you have a function

function [variable1, variable2, variable3, ...] = FunctionName(input1, input2, ...)

then when you run the function with appropriate inputs, MATLAB does not assign to variable1, variable2, variable3, ... in the workspace of the caller. Those variable names are completely local to the inside of the function, and stand in for the output names that the user provided when calling the function, such as

[x, y] = FunctionName(.....) %invoking the function

Here, whatever was assigned to variable1 inside the function will be assigned to x in the workspace where the function was invoked, and whatever was assigned to variable2 inside the function will be assigned to y in the workspace where the function was invoked. Whatever was assigned to variable3 inside the function will be ignored by the calling routine because there are no output slots to receive the value.

The names used inside the function have no connection to any variables with the same name in the calling routine. The connection is purely positional: the first variable in the output list in the function is transferred to the first output variable listed in the calling routine.

Simon Aldworth 2018-10-24

编辑：Simon Aldworth 2018-10-24

在 MATLAB Online 中打开

Thanks all.

dpb: you say you don't recommend it as a coding technique. What do you recommend? I had assumed that one would have a main code file that would call a gui to ask the user for data. This data would then be passed back to the main code for use and manipulation. Are you saying that all the code can be inside the gui code and that the main code is literally only for calling the gui?

My gui asks for 22 bits of information from the user. At the moment I have used the handles struct to store it, by adding fields:

% Set handles fields with initial values from UIcontrols
handles.mass = str2double(get(handles.editMassNom,'String'));
handles.pinertia = str2double(get(handles.editPInertiaNom,'String'));
handles.wb = str2double(get(handles.editWBNom,'String'));
etc, etc.

I then need to manipulate this data and, as said, have assumed that this is best done in the main code and workspace. So, following some initial processing of the data that isn't important here, I use assignin to pass all the information to the main workspace.

Is this appropriate? Or is there a neat way of getting the 22 bits of information stored within handles direct to the main workspace?

Regards,

Simon.

Stephen23 2018-10-24

编辑：Stephen23 2018-10-24

@Simon Aldworth: avoid using assignin, or any other method that magically makes data appear or disappear from another workspace. Read this to know some of the reasons why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Beginners often seem to love making data appear and disappear because they like to see all of their data in the base workspace. Experienced users handle all of the data within the GUI itself, which also leads to simpler, more robust, more efficient, less buggy code.

If you really want to return values to the base workspace then either use nested functions and waitfor (if you are sensibly writing your own GUI), or use the OutputFCN (if you are unfortunately using GUIDE).