RecyclerView smoothDesplácese hasta la posición en el centro. androide

Estoy usando un administrador de diseño horizontal para mi RecyclerView. necesito hacer RecyclerView de la siguiente manera: cuando haga clic en algún elemento, haga un desplazamiento suave hasta esa posición y coloque ese elemento en el centro de RecyclerView (si es posible, por ejemplo, 10 artículo de 20).

Entonces, no tengo ningún problema con smoothScrollToPosition()pero cómo poner el artículo que en el centro de RecyclerView???

¡Gracias!

Si es posible.

Al implementar RecyclerView.SmoothScrollermétodo de onTargetFound(View, State, Action).

/**
 * Called when the target position is laid out. This is the last callback SmoothScroller
 * will receive and it should update the provided {@link Action} to define the scroll
 * details towards the target view.
 * @param targetView    The view element which render the target position.
 * @param state         Transient state of RecyclerView
 * @param action        Action instance that you should update to define final scroll action
 *                      towards the targetView
 */
abstract protected void onTargetFound(View targetView, State state, Action action);

Específicamente en LinearLayoutManager con LinearSmoothScroller:

public class CenterLayoutManager extends LinearLayoutManager {

    public CenterLayoutManager(Context context) {
        super(context);
    }

    public CenterLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    public CenterLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
        RecyclerView.SmoothScroller smoothScroller = new CenterSmoothScroller(recyclerView.getContext());
        smoothScroller.setTargetPosition(position);
        startSmoothScroll(smoothScroller);
    }

    private static class CenterSmoothScroller extends LinearSmoothScroller {

        CenterSmoothScroller(Context context) {
            super(context);
        }

        @Override
        public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
            return (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2);
        }
    }
}

Mejoras a la respuesta – no hay necesidad de anular el LinearLayoutManager

De la respuesta anterior:

public class CenterSmoothScroller extends LinearSmoothScroller {

    public CenterSmoothScroller(Context context) {
        super(context);
    }

    @Override
    public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
        return (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2);
    }
}

Aquí cómo usarlo:

RecyclerView.LayoutManager lm = new GridLayoutManager(...): // or whatever layout manager you need

...

RecyclerView.SmoothScroller smoothScroller = new CenterSmoothScroller(recyclerView.getContext());

smoothScroller.setTargetPosition(position);

lm.startSmoothScroll(smoothScroller);

En caso de que alguien necesite el Equivalente de Kotlin de la clase en la respuesta aceptada.

class CenterLayoutManager : LinearLayoutManager {
    constructor(context: Context) : super(context)
    constructor(context: Context, orientation: Int, reverseLayout: Boolean) : super(context, orientation, reverseLayout)
    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)

    override fun smoothScrollToPosition(recyclerView: RecyclerView, state: RecyclerView.State, position: Int) {
        val centerSmoothScroller = CenterSmoothScroller(recyclerView.context)
        centerSmoothScroller.targetPosition = position
        startSmoothScroll(centerSmoothScroller)
    }

    private class CenterSmoothScroller(context: Context) : LinearSmoothScroller(context) {
        override fun calculateDtToFit(viewStart: Int, viewEnd: Int, boxStart: Int, boxEnd: Int, snapPreference: Int): Int = (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2)
    }
}

Según la respuesta de @Boda, si desea controlar la velocidad de desplazamiento suave (para una mejor animación), puede usar lo siguiente:

class CenterLayoutManager : LinearLayoutManager {
    constructor(context: Context) : super(context)
    constructor(context: Context, orientation: Int, reverseLayout: Boolean) : super(
        context,
        orientation,
        reverseLayout
    )

    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(
        context,
        attrs,
        defStyleAttr,
        defStyleRes
    )

    override fun smoothScrollToPosition(
        recyclerView: RecyclerView,
        state: RecyclerView.State,
        position: Int
    ) {
        val centerSmoothScroller = CenterSmoothScroller(recyclerView.context)
        centerSmoothScroller.targetPosition = position
        startSmoothScroll(centerSmoothScroller)
    }

    private class CenterSmoothScroller(context: Context) : LinearSmoothScroller(context) {
        override fun calculateDtToFit(
            viewStart: Int,
            viewEnd: Int,
            boxStart: Int,
            boxEnd: Int,
            snapPreference: Int
        ): Int = (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2)

        override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
            return MILLISECONDS_PER_INCH / displayMetrics.densityDpi
        }
    }

    companion object {
        // This number controls the speed of smooth scroll
        private const val MILLISECONDS_PER_INCH = 150f
    }
}

Uso:

recyclerView.layoutManager = CenterLayoutManager(requireContext(), LinearLayoutManager.HORIZONTAL, false)
recyclerView.smoothScrollToPosition(selectedPosition)

desde ahora (febrero de 2019), podría usar fácilmente este código en ListView

(ListView)word_list_view.smoothScrollToPositionFromTop(your_item_index, center_position.y);

RecyclerView no verificado, supongo que sería lo mismo.