uicontrol callback for more than one function - matlab

Question

I want to write a GUI program in Matlab and make 3 sliders on it with uicontrol and then write callbacks to use their 3 values in one command. I found a way to write a function for one slider as you can see in my program. Can you help me how use these 3 callbacks? (I use R2014a)
sld = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',0,...
'Position', [400 20 120 20],...
'Callback', #Blue);
sld = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',0,...
'Position', [400 60 120 20],...
'Callback', #Green);
sld = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',255,...
'Position', [400 100 120 20],...
'Callback', #Red);
function Red(source,~)
R = get(source,'Value');
end
function Green(source,~)
G = get(source,'Value');
end
function Blue(source,~)
B = get(source,'Value');
end
RGB = cat(3,R,G,B); %??????
Error: Undefined function or variable "R".

Answer 1

Persistent data must be stored somewhere that's accessible to the callback function. One common technique is to use the parent figure's UserData field. In the example above, once a slider has been moved, the current colour can be found in the RGB field of figure fh's UserData. Also, here only one callback is used, and the UI item is identified via its Tag.
fh = figure(1);
clf
%// Initialize figure's UserData
set(fh, 'UserData', struct('RGB', [0 0 0]));
sld_b = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',0,...
'Position', [400 20 120 20],...
'Callback', #colourHandler, 'Tag', 'blue');
sld_g = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',0,...
'Position', [400 60 120 20],...
'Callback', #colourHandler, 'Tag', 'green');
sld_r = uicontrol('Style', 'slider',...
'Min',0,'Max',255,'Value',255,...
'Position', [400 100 120 20],...
'Callback', #colourHandler, 'Tag', 'red');
%// This is in a separate file, colourHandler.m
function colourHandler(source, ~)
%// Find which slider triggered us
if strcmpi(get(source, 'Tag'), 'red')
ind = 1;
elseif strcmpi(get(source, 'Tag'), 'green')
ind = 2;
else
ind = 3;
end
%// update UserData
ud = get(get(source, 'Parent'), 'UserData');
ud.RGB(ind) = get(source, 'Value');
set(get(source, 'Parent'), 'UserData', ud);
end

Answer 2

Alternatively you can just store the handles of your graphics objects and use those to obtain the values in other functions.
For example:
function testcode
% Initialize sample GUI
h.fig = figure( 'MenuBar', 'none', 'ToolBar', 'none');
h.sld(1) = uicontrol( ...
'Parent', h.fig, ...
'Style', 'slider',...
'Min', 0, 'Max', 255, 'Value', 0, ...
'Units', 'Normalized', 'Position', [0.1 0.65 0.4 0.1], ...
'Tag', 'Red' ...
);
h.sld(2) = uicontrol( ...
'Parent', h.fig, ...
'Style', 'slider', ...
'Min', 0, 'Max', 255, 'Value', 0, ...
'Units', 'Normalized', 'Position', [0.1 0.45 0.4 0.1], ...
'Tag', 'Green' ...
);
h.sld(3) = uicontrol( ...
'Parent', h.fig, ...
'Style', 'slider', ...
'Min', 0, 'Max', 255, 'Value', 255, ...
'Units', 'Normalized', 'Position', [0.1 0.25 0.4 0.1], ...
'Tag', 'Blue' ...
);
% Use an axes object as a color display box
% Get starting RGB values for the color display, normalized so 0 <= x <= 1
startRGB = [get(h.sld(1), 'Value'), get(h.sld(2), 'Value'), get(h.sld(3), 'Value')]/255;
h.ax = axes( ...
'Parent', h.fig, ...
'Units', 'Normalized', 'Position', [0.6 0.36 0.3 0.3], ...
'XTickLabels', '', 'YTickLabels', '', ...
'Color', startRGB ...
);
% Need to set callback after all our elements are initialized
nsliders = length(h.sld);
set(h.sld, {'Callback'}, repmat({{#slidercallback, h}}, nsliders, 1));
end
function slidercallback(~, ~, h)
% Update background color of our axes object every time the slider is updated
RGB = [get(h.sld(1), 'Value'), get(h.sld(2), 'Value'), get(h.sld(3), 'Value')]/255;
set(h.ax, 'Color', RGB');
end
When callbacks execute they are passed 2 inputs by default, the invoking object and a structure of event data. As explained in the callback documentation, you can pass additional inputs to your callback by wrapping everything into a cell array. One thing to note is that the value of your variable being passed to the callback is its value as it exists when you define the callback. In other words, if we set the callback for our sliders at the same time we create them, when the callback for Red is fired h will only contain a handle to our figure, when the callback for Green is fired h will contain a handle to our figure and to the Red slider, and so on.
Because of this, you will see I have defined the callbacks once we have initialized all of our graphics objects. Using the curly brackets to set properties of multiple objects is explained in MATLAB's documentation for set. I use repmat so the size of the cell array is the same size as our array of slider objects.