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Scrolling Recipes

Scrolling to specific positions

To scroll to a specific position, use the selection methods from DpadRecyclerView:

  • setSelectedPosition - to scroll immediately to a given position
  • setSelectedPositionSmooth - to smooth scroll to a given position

If you're interested in triggering a callback once the selection is applied, you can do the following:

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recyclerView.setSelectedPosition(0, object : ViewHolderTask() {
    override fun execute(viewHolder: RecyclerView.ViewHolder) {
        // ViewHolder was selected and aligned to its final location
    }
})

Disabling smooth scrolling

DpadRecyclerView allows disabling smooth scrolling on focus changes with:

recyclerView.setSmoothFocusChangesEnabled(false)

This will make DpadRecyclerView scroll immediately without any animation to the new focused view.

Changing smooth scrolling behavior

The code below changes the default interpolator used for smooth scrolling to a linear interpolator:

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val linearInterpolator = LinearInterpolator()
recyclerView.setSmoothScrollBehavior(
    object : DpadRecyclerView.SmoothScrollByBehavior {
        override fun configSmoothScrollByDuration(dx: Int, dy: Int): Int {
            return RecyclerView.UNDEFINED_DURATION
        }

        override fun configSmoothScrollByInterpolator(dx: Int, dy: Int): Interpolator {
            return linearInterpolator
        }
    }
)

To slow down the smooth scrolling speed, check setSmoothScrollSpeedFactor:

recyclerView.setSmoothScrollSpeedFactor(2f)

The code above will make smooth scrolling twice slower.

Limiting number of pending alignments

Sometimes you might want to prevent the user from scrolling past too many items. You can specify the number of max pending alignments with: setSmoothScrollMaxPendingAlignments:

recyclerView.setSmoothScrollMaxPendingAlignments(2)

The code above translates to this behavior:

Max pending alignments

In the right scenario, there's just one next focusable view since the focused view still isn't aligned to the keyline.

Enabling layout during scrolling events

If you want to enable layout changes while DpadRecyclerView is still scrolling, use:

recyclerView.setLayoutWhileScrollingEnabled(true)

Long text scrolling

In some cases, you might need to show pages with text that should be scrollable (e.g terms & conditions).

For this use case, you can use DpadScroller:

val scroller = DpadScroller()
scroller.attach(dpadRecyclerView)

DpadScroller will scroll the page for you on key event presses without any alignment so that the user can read the entire content