Question

I save and load gui data as described in the manual using

function readImage(filename, hObject, handles)
  handles.image.data = imageRGBNoEdge;
  guidata(hObject,handles);

and

function createHistogram(handles)
  imageRGB = handles.image.data;

which are both called directly after the other

readImage(imageFile,hObject,handles);
createHistogram(handles);

However in he second function handles.image is unkown.

??? Reference to non-existent field 'image'.
Error in ==> ui_histogram>createHistogram at 252
imageRGB = handles.image.data;

But if I call the function a second time it is known?

Answer 1

Despite its name, handles is a structure and not a handle class so changing it within readImage does not propagate the change to the calling function.

You could either change readImage to be

function handles = readImage(filename, hObject, handles)

and call it with

handles = readImage(imageFile,hObject,handles);

or add a call to guidata

handles = guidata(hObject);

just before your calll to createHistogram.