MATLAB: How to find value of modifier with keypressfcn

guikeypressfcnmodifier

Hi, I'm trying to make a simple gui where 'tab' increases variable 'a' and 'shift+tab' decreases it.
Unfortunately, my code can't seem to pick up the shift modifier being pressed?
function varargout = modt(varargin)
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name',       mfilename, ...
                   'gui_Singleton',  gui_Singleton, ...
                   'gui_OpeningFcn', @modt_OpeningFcn, ...
                   'gui_OutputFcn',  @modt_OutputFcn, ...
                   'gui_LayoutFcn',  [] , ...
                   'gui_Callback',   []);
if nargin && ischar(varargin{1})
    gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
    [varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
    gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
function modt_OpeningFcn(hObject, eventdata, handles, varargin)
handles.a = 0;
guidata(hObject, handles);
function varargout = modt_OutputFcn(hObject, eventdata, handles) 
function figure1_KeyPressFcn(hObject, eventdata, handles)
handles = guidata(hObject);
if strcmp(eventdata.Key,'tab')
    handles.a = handles.a + 1
elseif strcmp(eventdata.Modifier{:},'shift') && strcmp(eventdata.Key,'tab')
    handles.a = handles.a - 1
end
guidata(hObject,handles)
Thanks for the help!

Best Answer

Lyn - look closely at your if/elseif
 if strcmp(eventdata.Key,'tab')
    handles.a = handles.a + 1
 elseif strcmp(eventdata.Modifier{:},'shift') && strcmp(eventdata.Key,'tab')
    handles.a = handles.a - 1
 end
For your elseif there are two conditions:
 strcmp(eventdata.Modifier{:},'shift') && strcmp(eventdata.Key,'tab')
So the code will decrement a by one if both conditions are true. BUT, the second condition is the (only) condition for the if statement! So your elseif will never evaluate because the if will always take precedence.
Try the following instead
 if strcmp(eventdata.Key,'tab')
    if isempty(eventdata.Modifier)
        handles.a = handles.a + 1
    elseif strcmp(eventdata.Modifier{:},'shift') 
        handles.a = handles.a - 1
    end
 end
Try the above and see what happens! Note that you can remove the line
 handles = guidata(hObject);
and just use the handles structure that is passed as the third input to this function.
Related Question