viewpager-scroll-duration.md

Customizing the Scroll Duration of ViewPager

First of all we need to extract the field mScroller from the ViewPager class so that we can start making changes on it.

Field mScroller = ViewPager.class.getDeclaredField("mScroller");

Now that we have the scroller we could in theory extract the field mDuration from it and apply our own preferred value, but unfortunately that will not work. The ViewPager explicitly passes the duration to the mScroller when requesting to scroll according to some calculations that I am not going to explain here. As a matter of fact, our duration value will be ignored. So we need to work around this limitation.

We can create our own CustomScroller by extending the Scroller class, and then associate it to the ViewPager.

mScroller.setAccessible(true);
mScroller.set(mPager, new CustomScroller(duration));

In this way we can define our preferred duration in the CustomScroller and use it in the overridden method startScroll() as shown below:

public class CustomScroller extends Scroller {

    private int mDuration;

    public CustomScroller(Context context, Interpolator interpolator, int duration) {
        super(context, interpolator);
        mDuration = duration;
    }

    @Override
    public void startScroll(int startX, int startY, int dx, int dy, int duration) {
        // Ignore received duration, use fixed one instead
        super.startScroll(startX, startY, dx, dy, mDuration);
    }
}

Credits: https://antoniocappiello.com/2015/10/31/spicy-up-your-viewpager-part-1-tune-the-scroll-duration/