MATLAB: The @ symbol within handles

handles

hello,

I cannot seem to figure out what the "@" means in handles

Here is the example code

set(handles.axisGroup, 'SelectionChangeFcn', @axisGroup_SelectionChangeFcn);

is that a pass by reference notation as in C++?

Thanks

Best Answer

No, it is not a pass-by-reference notation. It creates a function pointer object, with the function pointer object then being passed by value. The function pointer object may contain a lot more information than just a reference to the code: it may contain a complete p-coded version of the code and it may contain references to local variables.

Technically speaking, the @ notation creates a "closure" -- though it will be a near trivial closure if it is not being used as an anonymous function or if the routine being referenced does not have an 'end' statement matching the 'function' statement (which is interpreted as a signal to create a complete closure rather than to use the older style plain "reference to a routine")

Related Solutions

MATLAB: How to use local functions in GUI in order to organize callbacks in mutliple .m files

function main_OpeningFcn(hObject, eventdata, handles, varargin)
SubCallbacks = SubCallbacks_Cntrl;
set(handles.checkbox1,   'Callback', SubCallbacks.checkbox1_Callback)
set(handles.pushbutton1, 'Callback', SubCallbacks.pushbutton1_Callback)

Then add this in each callback to obtain the current value of the handles struct:

function checkbox1_Callback(hObject, evt)
handles = guidata(hObject);
...

Alternatively you can use a wrapper function: Define the same function for all callbacks and branch by using an additional argument:

function SubCallbacks_Cntrl(hObject, EventData, ObjectName)
handles = guidata(hObject)
switch ObjectName
  case 'pushbutton1'
    pushbutton1_Callback(hObject, EventData, handles)
  case 'checkbox1'
    checkbox1_Callback(hObject, EventData, handles)
  ...
end

And the single callbacks are following. You could use the tag of the object also:

switch hObject.Tag
  ...

MATLAB: How to pass a variable between a m-file and another m-file that runs a gui

M files can contain scripts or functions but variables can only be passed to functions so the m-file must be written as a function [see Scripts vs Functions and Create Function in Files].

For example,

mfile2

function [output] = mfile2(input) 
    % add 1 to the input and pass the result to mfile2.
    y = input + 1; 
    
    % Send y to mfile1 and get the result
    % mfile1 divides y by 2 to z equals (input+1)/2
    z = mfile1(y);
   
end

mfile1

function [output] = mfile1(input)
    % divide the input by two
    output = input/2;
end

All variables needed in a function must either be passed into the function as inputs or defined within the function. If your functions interact with your GUI, pass the handle structure into the function.

Best Answer

Related Solutions

MATLAB: How to use local functions in GUI in order to organize callbacks in mutliple .m files

MATLAB: How to pass a variable between a m-file and another m-file that runs a gui

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