Callback function not seeing App Data

I am trying to pass data to/from a Callback function for my GUI. I am using App Data with setappdata and getappdata. I have looked at the demo and mimicked it precisely. However, the Callback subfunction is not seeing the App Data. Here is a simplified version of my code that demonstrates my problem:

function [] = system_modelling3 ()
    clear all
    close all
    clc

      f = figure('Visible','on','Position', [200 200 200 50]); % create figure

      system_parameters = struct('initilized',1); % initialize non-empty structure
      setappdata(f,'system_parameters',system_parameters) % set App Data

      system_parameters.file_vmodel = 'vmodel.m'; % add field to structure
      setappdata(f,'system_parameters',system_parameters); % update App Data

      fprintf('\n\nMain function sets the App Data as: \n')
      output = getappdata(f,'system_parameters') % confirm that App Data updated

      % gui controls
      selectvmodel = uicontrol(f,'Style','pushbutton','String','Load any file.','Position', [10 10 100 20],'Callback',{@selectvmodel_Callback});

function selectvmodel_Callback(f,eventdata)
    temp = getappdata(f,'system_parameters'); % get App Data
    temp.newfile_vmodel = uigetfile('*','Load any file.'); % remove extension from file
    setappdata(f,'system_parameters',temp) % update App Data

      fprintf('\n\nCallback updates App Data as :\n')
      output = getappdata(f,'system_parameters') % confirm that App Data updated

Answer 1

[Walter Roberson]

In your callback, you getappdata() against f, which is the first parameter of the callback. The first parameter of a uicontrol callback is always the handle of the source of the callback, which is to say the object whose callback it is, the uicontrol. You are attempting to get the appdata of the uicontrol. But the uicontrol does not have any appdata: you attached the appdata to the figure.

Moral of the story: it is probably better to stick to "src" or "hObject" for the name of the first parameter of normal callbacks, to remind yourself that the parameter is being supplied automatically and has no association with any like-named variable in any other routine.

function selectvmodel_Callback(src, eventdata)
f = ancestor(src, 'figure');