Android Material Slider OnChangeListener Response Delay/Skip Problem

Question

So I have a "both" Slider which controls "width" Slider and "length" Slider, like below:

<com.google.android.material.slider.Slider
    android:id="@+id/width_slider"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:value="40"
    android:valueFrom="0"        <-
    android:valueTo="200"        <-
    android:stepSize="1"/>       <-

<com.google.android.material.slider.Slider
    android:id="@+id/height_slider"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:value="40"
    android:valueFrom="0"        <-
    android:valueTo="200"        <-
    android:stepSize="1"/>       <-

<com.google.android.material.slider.Slider
    android:id="@+id/both_slider"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:value="100"   
    android:valueFrom="0"        <-
    android:valueTo="200"        <-
    android:stepSize="1"/>       <-

As I marked above, they all have same range (from & to) and the stepSize to 1 (important), and I set the behavior of

when adding/subtracting value 1 on the both Slider, the other two will be added/subtracted value 1 too.

Code as below:

private var previousValue = 50f        //initial value, same as on xml

binding.bothSlider.addOnChangeListener { slider, value, fromUser ->
    if (value > previousValue) {
        binding.widthSlider.value++
        binding.heightSlider.value++
    }

    if (value < previousValue) {
        binding.widthSlider.value--
        binding.heightSlider.value--
    }

    previousValue = value
}

And weird thing happens, it seems like the width and height Slider has some a bit slow reaction (I guess), and skip some point:

They should be synchronized, because they have same stepSize and value range (just the initial values are different). Any help would be appreciated.

Probably your listener is called less frequently than you think. That is, if the slider is at 50 and you drag it to 70 very quickly, it is probably called ~3 times, not 20 times. — Ben P., Jan 16 '21 at 22:38

Ben P. · Answer 1 · 2021-01-18T00:11:18.490

4

Use the current value of the "both" slider to set the values of the others.

binding.bothSlider.addOnChangeListener { _, value, _->
    binding.widthSlider.value = value
    binding.heightSlider.value = value
}

It's a little hard to know exactly what you're trying to do. You could also do something similar to what you have but use a diff instead of just 1:

binding.bothSlider.addOnChangeListener { slider, value, fromUser ->
    val diff = value - previousValue
    binding.widthSlider.value += diff
    binding.heightSlider.value += diff

    previousValue = value
}

This will let the sliders diverge but will still solve the "speed" problem you're having.

edited Jan 18 '21 at 00:11

answered Jan 17 '21 at 23:50

Ben P.

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This is a whole lot more elegant, but the issue with the initial offset would persist. – Martin Zeitler Jan 18 '21 at 00:08
Thank you for the solution, I just found out that my `previousValue` didn't match the xml initial value...such a stupid mistake, sorry for that. – Sam Chen Jan 19 '21 at 03:59

score 2 · Answer 2 · answered Jan 17 '21 at 23:59

2

Those sliders seem to have a different scale...

but actually it's the initial value which creates an offset of 60:

<com.google.android.material.slider.Slider
    android:id="@+id/both_slider"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:value="40" <-- 100 != 40
    android:valueFrom="0"
    android:valueTo="200"
    android:stepSize="1"/>

answered Jan 17 '21 at 23:59

Martin Zeitler

1
19
155
216

Thank you for the solution, I just found out that my `previousValue` didn't match the xml initial value (100) ...such a stupid mistake, sorry for that. – Sam Chen Jan 19 '21 at 03:59

Android Material Slider OnChangeListener Response Delay/Skip Problem

2 Answers2