Issue in Refresh CData of HGimage - matlab

Question

Initially I am create a figure in GUI with two button (btnStart , btnNext ) and one axes (P_axes). For above two buttons I am using callback function.
In first button callback Function
function btnStart_callback(hObject,eventdata ,handles)
load MRI;
d = D(:,:,1);
handles.Img = imshow(d,'Parent' , P_axes);
setappdata(handles.figure1 , 'Indx' , 1)
setappdata(handles.figure1 , 'Data' , D)
end
In second button callback Function
function btnNext_callback(hObject,eventdata ,handles)
indx = getappdata(handles.figure1 , 'Indx');
D= getappdata(handles.figure1 , 'Data');
d = D(:,:,indx+1);
set(handles.Img , 'CData',d);
setappdata(handles.figure1 , 'Indx' , indx+1);
end
In the second callback function i got one in the line set(handles.Img , 'CData',d);
error is "Invalid or deleted object. "
why this error is occur and how to solve it ?

Answer 1

As mentioned by Rattus Ex Machina that's hard to debug without seeing the rest of your code. If that could be of any help, here is a simple GUI which does what you seem to be after. Take the time to play around with it to see what might have caused the error in your code. I suspect that's a basic issue but I think it comes form elsewhere in the code than the part you have shown.
function LoadMRIGUI
clc
clear all
handles.figure1 = figure('Position',[100 100 400 400],'Units','normalized');
P_axes = axes('Units','normalized','Position',[.2 .2 .6 .6]);
handles.ButtonStart= uicontrol('Style','push','String','Start','Position',[40 350 50 30],'Callback',#(s,e) btnStart_callback);
handles.ButtonStop= uicontrol('Style','push','String','Next','Position',[100 350 50 30],'Callback',#(s,e) btnNext_callback);
%// === NEW === \\%
%// text box to see current index
handles.IdxTitle = uicontrol('Style','text','String','Index','Position',[160 350 50 20]);
handles.Idxbox = uicontrol('Style','text','String','1','Position',[220 350 50 20]);
function btnStart_callback
%// === NEW === \\%
S = load('mri');
d = S.D(:,:,1);
handles.Img = imshow(d,'Parent' , P_axes);
setappdata(handles.figure1 , 'Indx' , 1)
setappdata(handles.figure1 , 'Data' , S.D)
end
function btnNext_callback
indx = getappdata(handles.figure1 , 'Indx');
D= getappdata(handles.figure1 , 'Data');
d = D(:,:,indx+1);
set(handles.Img , 'CData',d);
setappdata(handles.figure1 , 'Indx' , indx+1);
set(handles.Idxbox,'String',num2str(indx+1));
end
end
Sample screenshot:
Hope that helps!

Answer 2

Without seeing the context, it's tough to be absolutely sure what you're up to. Importantly, are these functions defined in the same, or different, files? There does seem to be an obvious problem which could cause the error you are seeing:
function btnStart_callback(hObject,eventdata ,handles)
load MRI;
d = D(:,:,1);
handles.Img = imshow(d,'Parent' , P_axes);
setappdata(handles.figure1 , 'Indx' , 1)
setappdata(handles.figure1 , 'Data' , D)
end
In the above, handles is passed in, modified, and then discarded when the function ends. If the functions are defined in different files, that value you store in .Img will never be seen again, which is why your second callback is throwing an error when you try to use it.
You are using the appdata approach for sharing data between the two functions. This will certainly work, but if you are using that approach you need also to share handles.Img.
An alternative approach, that I would favour, would be to place both of these callbacks as nested functions inside the main file representing your "application" (which creates the GUI, etc.). That way, they can share data at the file scope level (variables defined in the root function are visible in nested functions) and you don't need all the calls to appdata functions.
Your application would take this form:
function myapp
% define a variable here
my_handle = [];
function callback1(h, e)
% and it is visible here
my_handle = gcf;
end
function callback2(h, e)
% and also here
set(my_handle, 'monkeys', 'maximum');
end
end