matlab eventdata of uitable returned empty - matlab

Question

I'm trying to run a GUIDE app in Matlab, but I encounter a problem: when I try to access the location of the selected cell in a ui table, the variable holding it (eventdata.Indices) quickly changes back to an empty vector.
Here's my CellSelectionCallback function:
function varargout = ChannelMatrix(varargin)
% CHANNELMATRIX MATLAB code for ChannelMatrix.fig
% CHANNELMATRIX, by itself, creates a new CHANNELMATRIX or raises the existing
% singleton*.
%
% H = CHANNELMATRIX returns the handle to a new CHANNELMATRIX or the handle to
% the existing singleton*.
%
% CHANNELMATRIX('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in CHANNELMATRIX.M with the given input arguments.
%
% CHANNELMATRIX('Property','Value',...) creates a new CHANNELMATRIX or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before ChannelMatrix_OpeningFcn gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to ChannelMatrix_OpeningFcn via varargin.
%
% *See GUI Options on GUIDEs Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help ChannelMatrix
% Last Modified by GUIDE v2.5 14-Oct-2015 17:06:14
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', #ChannelMatrix_OpeningFcn, ...
'gui_OutputFcn', #ChannelMatrix_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
% --- Executes just before ChannelMatrix is made visible.
function ChannelMatrix_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% varargin command line arguments to ChannelMatrix (see VARARGIN)
clc
% Choose default command line output for ChannelMatrix
handles.output = hObject;
%CONNECT TO SWITCHER
matrixes=cell(12,6,26);
setappdata(0,'matrixes',matrixes);
set(handles.listbox1,'Value',1);
setappdata(0,'index_selected',1); %force Alpha for deafult selection
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes ChannelMatrix wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = ChannelMatrix_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --- Executes when selected cell(s) is changed in uitable1.
function uitable1_CellSelectionCallback(hObject, eventdata, handles)
% hObject handle to uitable1 (see GCBO)
% eventdata structure with the following fields (see UITABLE)
% Indices: row and column indices of the cell(s) currently selecteds
% handles structure with handles and user data (see GUIDATA)
% --- Executes when selected cell(s) is changed in uitable1.
try
currow = eventdata.Indices(1);
curcol = eventdata.Indices(2);
adata=get(handles.uitable1,'Data');
if adata{currow,curcol} == 'V'
adata{currow,curcol} = '';
else
adata{currow,curcol} = 'V';
end
set(hObject,'Data',adata);
end
% --- Executes on button press in cls_ch.
function cls_ch_Callback(hObject, eventdata, handles)
% hObject handle to cls_ch (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
index_selected = getappdata(0,'index_selected'); %get the number of selected item in listbox
matrixes = getappdata(0,'matrixes'); %get current selection of measurments
table = get(handles.uitable1,'data'); %get the selected channels for this measure
for i=3:14
for j=1:6
if table{i-2,j}=='V'
matrixes{i-2,j,index_selected}='V'; %preform scan and check - add to matrixes selcted values
end
end
end
%save changes
set(handles.uitable3,'Data',matrixes(:,:,index_selected));
setappdata(0,'matrixes',matrixes);
guidata(hObject, handles);
% --- Executes on button press in opn_ch.
function opn_ch_Callback(hObject, eventdata, handles)
% hObject handle to opn_ch (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
index_selected = getappdata(0,'index_selected'); %get the number of selected item in listbox
matrixes = getappdata(0,'matrixes'); %get current selection of measurments
table = get(handles.uitable1,'data'); %get the selected channels for this measure
for i=3:14
for j=1:6
if table{i-2,j}=='V'
matrixes{i-2,j,index_selected}=''; %preform scan and check - add to matrixes selcted values
end
end
end
%save changes
set(handles.uitable3,'Data',matrixes(:,:,index_selected));
setappdata(0,'matrixes',matrixes);
guidata(hObject, handles);
% --- Executes on button press in opn_all.
function opn_all_Callback(hObject, eventdata, handles)
% hObject handle to opn_all (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
matrixes=cell(12,6,26);
setappdata(0,'matrixes',matrixes); %sets up a new matrix
set(handles.uitable1,'Data',cell(12,6));
set(handles.uitable3,'Data',cell(12,6));
set(handles.listbox1,'Value',1);
guidata(hObject, handles);
% --- Executes on button press in clr_selection_btn.
function clr_selection_btn_Callback(hObject, eventdata, handles)
% hObject handle to clr_selection_btn (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
set(handles.uitable1,'Data',cell(12,6));
% --- Executes on selection change in listbox1.
function listbox1_Callback(hObject, eventdata, handles)
% hObject handle to listbox1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: contents = cellstr(get(hObject,'String')) returns listbox1 contents as cell array
% contents{get(hObject,'Value')} returns selected item from listbox1
matrixes=getappdata(0,'matrixes');
index_selected=get(hObject,'Value');
setappdata(0,'index_selected',index_selected);
set(handles.uitable3,'Data',matrixes(:,:,index_selected));
set(handles.uitable1,'Data',cell(12,6));
guidata(hObject, handles);
% --- Executes during object creation, after setting all properties.
function listbox1_CreateFcn(hObject, eventdata, handles)
% hObject handle to listbox1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: listbox controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
What's wrong here?
Thanks!

Answer 1

I think there is nothing anything wrong in the definition of your uitable1_CellSelectionCallback function.
I've built a simple GUI consisting of just a uitable and executing step by step the callback in debug mode this is what actually happens:
when you left-click on a cell's table, the uitable1_CellSelectionCallback is correctly called
everything goes right up to the set(hObject,'Data',adata); instruction and eventdata.Indices array contains the row and column index of the selected cell (ref. to the Function Call Stack in the following picture)
as the set(hObject,'Data',adata); function is executed, automatically a new call to uitable1_CellSelectionCallback is made by MatLab (probably somehow triggered by set. In the next picture, you can see the second (recursive) call to uitable1_CellSelectionCallback in the Function Call Stack and the white and green pair of arrows in the edit window the debug mode
since the second call is not generated by an actual user selection of a cell, the eventdata.Indices is empty therefore an error is generated when the currow = eventdata.Indices(1); is executed
So, this is why when you click on a cell, its content is correctly set to "V" or to an empty string as you expeced but, at the same time (actually, after the time MatLab needs to make second call to uitable1_CellSelectionCallback) the GUI crashes.
I do not know if this might be considered a MatLab's bug, nevertheless I did not find any way to prevent the second call to uitable1_CellSelectionCallback.
A possible solution, not so far from yours (using try-catch) could be insert the present callback code in a if block checking if isempty(eventdata.Indices) (that is to replace try with if).
This will prevent the second call be "effective" and the generation of the error, which is not avoided by using try-catch (even if does not prevent the second call to happen).
Hope this helps.