How can i control the scrolling speed of recyclerView.smoothScrollToPosition(position)

Question

I have a recycler view... and i want a smooth scrolldown and then scrollup to it programatically to show the complete content in it to user .... And i m able to do this by<

Answer 1

Just to improve on the answer a little:

public class SpeedyLinearLayoutManager extends LinearLayoutManager {

    private static final float MILLISECONDS_PER_INCH = 5f; //default is 25f (bigger = slower)

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

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

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

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {

        final LinearSmoothScroller linearSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {

            @Override
            public PointF computeScrollVectorForPosition(int targetPosition) {
                return super.computeScrollVectorForPosition(targetPosition);
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
            }
        };

        linearSmoothScroller.setTargetPosition(position);
        startSmoothScroll(linearSmoothScroller);
    }
}

And then set SpeedyLayoutManager to your RecyclerView:

recyclerView.setLayoutManager(new SpeedyLinearLayoutManager(context, SpeedyLinearLayoutManager.VERTICAL, false);

Answer 2

I've made a version that you can set the scrolling speed variable.

If you set factor to 2, it will be twice as slow as default.

public class VariableScrollSpeedLinearLayoutManager extends LinearLayoutManager {

    private final float factor;

    public VariableScrollSpeedLinearLayoutManager(Context context, float factor) {
        super(context);
        this.factor = factor;
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {

        final LinearSmoothScroller linearSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {

            @Override
            public PointF computeScrollVectorForPosition(int targetPosition) {
                return VariableScrollSpeedLinearLayoutManager.this.computeScrollVectorForPosition(targetPosition);
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return super.calculateSpeedPerPixel(displayMetrics) * factor;
            }
        };

        linearSmoothScroller.setTargetPosition(position);
        startSmoothScroll(linearSmoothScroller);
    }
}

Answer 3

I got it like this horizontally

  private val milliSecondsPerInch = 500f 
  var horizontalLayoutManager =  LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false)

onCreate

horizontalLayoutManager =  LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false)
recycler_banner?.layoutManager = horizontalLayoutManager

and then

val linearSmoothScroller: LinearSmoothScroller =
object : LinearSmoothScroller(this) {
    override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
        return milliSecondsPerInch / displayMetrics.densityDpi
    }
}
linearSmoothScroller.targetPosition = 3 //the last position of the item in the list
horizontalLayoutManager.startSmoothScroll(linearSmoothScroller)

Answer 4

I found an answer!

You need to make a custom class extending [LinearLayoutManager][1] and then override the [smoothScrollToPosition][1] method. Inside, you need to create a new [LinearSmoothScroller][1] and override its calculateSpeedPerPixel method Then use that LinearSmoothScroller to complete the scroll.

Here is my example :

public class CustomLinearLayoutManager extends LinearLayoutManager{
        @Override
        public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
            final LinearSmoothScroller linearSmoothScroller =
                    new LinearSmoothScroller(recyclerView.getContext()) {
                        private static final float MILLISECONDS_PER_INCH = 100f;

                        @Override
                        public PointF computeScrollVectorForPosition(int targetPosition) {
                            return CustomLinearLayoutManager.this
                                .computeScrollVectorForPosition(targetPosition);
                    }

                    @Override
                    protected float calculateSpeedPerPixel
                            (DisplayMetrics displayMetrics) {
                        return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
                    }
                };
        linearSmoothScroller.setTargetPosition(position);
        startSmoothScroll(linearSmoothScroller);
    }
}

Assign this CustomLinearLayoutManager to your RecyclerView and you should be good to go. Let me know if I was unclear in anything. I'll be happy to help.

Answer 5

For those uninterested in overriding LinearLayoutManager (or whichever subclass you're using), you can just call startSmoothScroll(smoothScroller) directly on the layout manager.

LinearSmoothScroller linearSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {

    @Override
    protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
        return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
    }
};

linearSmoothScroller.setTargetPosition(position);
layoutManager.startSmoothScroll(linearSmoothScroller);