How To Use Matlab GUI Slider Trough - matlab

Question

I am trying to slide through images that I loaded into the GUI. When images are loaded into the GUI, I updated the slider parameters like this.
part of the "function" for image loading
if handles.nImages > 1
set(handles.frameSlider,'Min',1,'Max',handles.nImages,'Value',1)
handles.sliderStep = [1 1]/(handles.nImages - 1);
set(handles.frameSlider,'SliderStep',handles.sliderStep)
end
Then trying to slide through images and the slider arrow keys work fine but the pulling the slider trough doesn't work when I did this. When I pull the slider trough, the pull is smooth without any step-incremented sensations. It is giving me this error: Subscript indices must either be real positive integers or logicals. I think this is happening because when I pull the trough, I am setting it at values between the allowable slider increments since the pull is not step-incremented.
part of the "function" for slider pulling
sliderPosition = get(handles.frameSlider,'Value');
imagesc(handles.imageListPhs{indexes})
What could be the error?

Answer 1

The step size of the slider only governs how it behaves when the user clicks the arrow buttons or inside the slider trough. The location of the thumb when the user drags it is not governed by the step size so it will most likely return a non-integer, which cannot be used as an index. You will need to use a rounding function, like round, ceil, floor, or fix to convert the slider value into one that is valid for indexing.
Consider the following example:
function testcode
nA = 15;
myfig = figure('MenuBar', 'none', 'ToolBar', 'none', 'NumberTitle', 'off');
lbl(1) = uicontrol('Parent', myfig, 'Style', 'text', ...
'Units', 'Normalized', 'Position', [0.1 0.7 0.8 0.2], ...
'FontSize', 24, 'String', 'Selected Value:');
lbl(2) = uicontrol('Parent', myfig, 'Style', 'text', ...
'Units', 'Normalized', 'Position', [0.1 0.4 0.8 0.2], ...
'FontSize', 24, 'String', 'Rounded Value:');
uicontrol('Parent', myfig, 'Style', 'Slider', ...
'Units', 'Normalized', 'Position', [0.1 0.1 0.8 0.2], ...
'Min', 1, 'Max', nA, 'SliderStep', [1 1]/(nA - 1), 'Value', 1, ...
'Callback', {#clbk, lbl});
end
function clbk(hObject, ~, lbl)
slider_value = get(hObject, 'Value');
slider_value_rnd = round(slider_value);
set(lbl(1), 'String', sprintf('Selected Value: %.2f\n Can I Index with this? %s', ...
slider_value, canIindexwiththis(slider_value)));
set(lbl(2), 'String', sprintf('Rounded Value: %.2f\n Can I Index with this? %s', ...
slider_value_rnd, canIindexwiththis(slider_value_rnd)));
set(hObject, 'Value', slider_value_rnd); % Snap slider to correct position
end
function [yesno] = canIindexwiththis(val)
try
A(val) = 0;
catch
yesno = 'No!';
return
end
yesno = 'Yes!';
end
which illustrates the process: