App Designer: Create a Discrete Slider

Background:

Attemtping to develop a survey using MATLAB App Designer. The goal is to ask a user to rate a photo shown from 1-10.

What I'm trying to do:

Create a Slider that would only fix itself to discrete values and store this rating to later on tabulate survey results.

About me:

I'm new to the App Designer of MATLAB, so I'm not really too familiar with the syntax and some keywords, a dumbed down explanation would be much appreciated.

-- Design View --

[Kojiro Saito]

I think you could create a discrete slider whose values are 0~10. Where do you get stucked?

[Andres Bergsneider]

Hi Kojiro, thank you for your prompt response.

The only slider option I see (picutred above) is continiuous. Meaning it will stay placed wherever the user has dropped the arrow key. I'm hoping it would snap to one of the integer values.

-- Screenshot of the Issue --

Answer 1

[Adam Danz]

Just be aware that there are discrete knobs (properties) in app designer. But if you want a discrete slider....

Instructions how to make a continuous slider behave as if it were discrete

1) Add the slider to your app in app designer.

2) In the Inspector window, set the Limits, MajorTicks and MajorTickLabels to the discrete values of your choice and remove the MinorTicks since they do not make sense with discrete options.

3) Add a Value Changed callback function by right-clicking the slider > callbacks > Add ValueChangedFcn callback. This will add the new function in Code View.

4) From the Code View, modify the newly added function so that it always snaps to the nearest discrete value on the slider. You can copy-paste the following function except for the first and last line.

function SliderValueChanged(app, event)
    value = app.Slider.Value;
    % determine which discrete option the current value is closest to.
    [~, minIdx] = min(abs(value - event.Source.MajorTicks(:)));
    % move the slider to that option
    event.Source.Value = event.Source.MajorTicks(minIdx);
    % Override the selected value if you plan on using it within this function
    value = event.Source.MajorTicks(minIdx);
end

[Andres Bergsneider]

Adam, what a great breakdown!

Thank you very much for taking your time in helping me out, it totally worked!!

[Adam Danz]

Thanks for the feedback, Andres!

[Roche de Guzman]

In the callback, you can just round the value then replace it back:

value = round(app.Slider.Value); % get then round

app.Slider.Value = value; % set

[Adam Danz]

That's true only for consecutive integer ticks.

Consider this set of ticks that are not integers nor at a fixed interval:

[0, 0.25, 0.5, 0.75, 1, 1.5]

or

[0 2 4 6 8 10]

[Nitin Phadkule]

The problem with rounding the value is, the rounded value are rounded for displaying only, buttheir decimal values are still there so rounded values cant be used in if, if else statement for checking equal to value.

Thanks Adam Danz, your answer also helped me to discetise the Knob.

The problem with rounding the value is, the rounded value are rounded for displaying only, buttheir decimal values are still there so rounded values cant be used in if, if else statement for checking equal to value.

[Adam Danz]

Thanks for the feedback.

Just FYI, AppDesigner already offers discrete knobs (there's a link in the first sentence of my answer).

[Mohammad Mainul]

thank you so much Mr. Adam. Your answer helped me a lot.