Matlab GUI callback troubles

Question

I try to make the uipanel change boarder colors while pressing and releasing mouse button on elsewhere except inputs and panel buttons.

function    [oldpropvalues,varargout]=DisableFigure(handlearray,prop,propvalue,varargin);

  oldpropvalues=get(handlearray,prop);

  %this IF is used to highlight the "modal" panel when anywhere outside it is pressed

  if length(varargin)==2  

    %these two are the old windowbutton functions which will be put back when the window is put back to normal.
    varargout{1}=get(varargin{1},'windowbuttondownfcn');    
    varargout{2}=get(varargin{1},'windowbuttonupfcn');

    set(varargin{1},'windowbuttondownfcn',['set(varargin{2},''bordertype'',''line'',''borderwidth'',2,''highlightcolor'',[0 0 0])']);
    set(varargin{1},'windowbuttonupfcn',['set(varargin{2},''bordertype'',''beveledout'',''borderwidth'',1,''highlightcolor'',[1 1 1])']);

  end 

  set(handlearray,prop,propvalue);

The error shows Undefined variable "varargin" or class "varargin".

Error while evaluating Figure WindowButtonDownFcn

Undefined variable "varargin" or class "varargin".

Error while evaluating Figure WindowButtonUpFcn

Answer 1

Your problem is that you're defining your window callbacks as character vectors, which are evaluated in the base workspace where the variable varargin doesn't exist. You can define them as anonymous functions instead:

set(varargin{1}, 'WindowButtonDownFcn', ...
    @(~, ~) set(varargin{2}, 'BorderType', 'line', 'BorderWidth', 2, ...
                'HighlightColor', [0 0 0]));
set(varargin{1}, 'WindowButtonUpFcn', ...
    @(~, ~) set(varargin{2}, 'BorderType', 'beveledout', 'BorderWidth', 1, ...
                'HighlightColor', [1 1 1]));

Answer 2

You did not show how you produced the error, but from the error message, I guess you called the function with less than 4 input arguments. Then varargin does not exist, so matlab gives the error.

To avoid the error, you need to check nargin before you use varargin, for example, replace your if statement line with

if nargin==5 % so length(varargin)==2