RecyclerView - How to smooth scroll to top of item on a certain position?

问题

On a RecyclerView, I am able to suddenly scroll to the top of a selected item by using:

((LinearLayoutManager) recyclerView.getLayoutManager()).scrollToPositionWithOffset(position, 0);

However, this abruptly moves the item to the top position. I want to move to the top of an item smoothly.

I\'ve also tried:

recyclerView.smoothScrollToPosition(position);

but it does not work well as it does not move the item to the position selected to the top. It merely scrolls the list until the item on the position is visible.

回答1:

RecyclerView is designed to be extensible, so there is no need to subclass the LayoutManager (as droidev suggested) just to perform the scrolling.

Instead, just create a SmoothScroller with the preference SNAP_TO_START:

RecyclerView.SmoothScroller smoothScroller = new LinearSmoothScroller(context) {
  @Override protected int getVerticalSnapPreference() {
    return LinearSmoothScroller.SNAP_TO_START;
  }
};

Now you set the position where you want to scroll to:

smoothScroller.setTargetPosition(position);

and pass that SmoothScroller to the LayoutManager:

layoutManager.startSmoothScroll(smoothScroller);

回答2:

for this you have to create a custom LayoutManager

public class LinearLayoutManagerWithSmoothScroller extends LinearLayoutManager {

    public LinearLayoutManagerWithSmoothScroller(Context context) {
        super(context, VERTICAL, false);
    }

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

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

    private class TopSnappedSmoothScroller extends LinearSmoothScroller {
        public TopSnappedSmoothScroller(Context context) {
            super(context);

        }

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

        @Override
        protected int getVerticalSnapPreference() {
            return SNAP_TO_START;
        }
    }
}

use this for your RecyclerView and call smoothScrollToPosition.

example :

 recyclerView.setLayoutManager(new LinearLayoutManagerWithSmoothScroller(context));
 recyclerView.smoothScrollToPosition(position);

this will scroll to top of the RecyclerView item of specified position.

hope this helps.

回答3:

We can try like this

    recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView,new RecyclerView.State(), recyclerView.getAdapter().getItemCount());

回答4:

This is an extension functions I wrote in Kotlin to call directly on RecyclerView (based on @Paul Woitaschek answer):

fun RecyclerView.smoothSnapToPosition(position: Int, snapMode: Int = LinearSmoothScroller.SNAP_TO_START) {
    val smoothScroller = object: LinearSmoothScroller(this.context) {
        override fun getVerticalSnapPreference(): Int {
            return snapMode
        }

        override fun getHorizontalSnapPreference(): Int {
            return snapMode
        }
    }
    smoothScroller.targetPosition = position
    layoutManager?.startSmoothScroll(smoothScroller)
}

Use it like this:

myRecyclerView.smoothSnapToPosition(itemPosition)

回答5:

The easiest way I've found to scroll a RecyclerView is as follows:

// Define the Index we wish to scroll to.
final int lIndex = 0;
// Assign the RecyclerView's LayoutManager.
this.getRecyclerView().setLayoutManager(this.getLinearLayoutManager());
// Scroll the RecyclerView to the Index.
this.getLinearLayoutManager().smoothScrollToPosition(this.getRecyclerView(), new RecyclerView.State(), lIndex);

回答6:

Override the calculateDyToMakeVisible/calculateDxToMakeVisible function in LinearSmoothScroller to implement the offset Y/X position

override fun calculateDyToMakeVisible(view: View, snapPreference: Int): Int {
    return super.calculateDyToMakeVisible(view, snapPreference) - ConvertUtils.dp2px(10f)
}

回答7:

i Used Like This :

recyclerView.getLayoutManager().smoothScrollToPosition(recyclerView, new RecyclerView.State(), 5);

回答8:

Thanks, @droidev for the solution. If anyone looking for Kotlin solution, refer this:

    class LinearLayoutManagerWithSmoothScroller: LinearLayoutManager {
    constructor(context: Context) : this(context, VERTICAL,false)
    constructor(context: Context, orientation: Int, reverseValue: Boolean) : super(context, orientation, reverseValue)

    override fun smoothScrollToPosition(recyclerView: RecyclerView?, state: RecyclerView.State?, position: Int) {
        super.smoothScrollToPosition(recyclerView, state, position)
        val smoothScroller = TopSnappedSmoothScroller(recyclerView?.context)
        smoothScroller.targetPosition = position
        startSmoothScroll(smoothScroller)
    }

    private class TopSnappedSmoothScroller(context: Context?) : LinearSmoothScroller(context){
        var mContext = context
        override fun computeScrollVectorForPosition(targetPosition: Int): PointF? {
            return LinearLayoutManagerWithSmoothScroller(mContext as Context)
                    .computeScrollVectorForPosition(targetPosition)
        }

        override fun getVerticalSnapPreference(): Int {
            return SNAP_TO_START
        }


    }

}

回答9:

Probably @droidev approach is the correct one, but I just want to publish something a little bit different, which does basically the same job and doesn't require extension of the LayoutManager.

A NOTE here - this is gonna work well if your item (the one that you want to scroll on the top of the list) is visible on the screen and you just want to scroll it to the top automatically. It is useful when the last item in your list has some action, which adds new items in the same list and you want to focus the user on the new added items:

int recyclerViewTop = recyclerView.getTop();
int positionTop = recyclerView.findViewHolderForAdapterPosition(positionToScroll) != null ? recyclerView.findViewHolderForAdapterPosition(positionToScroll).itemView.getTop() : 200;
final int calcOffset = positionTop - recyclerViewTop; 
//then the actual scroll is gonna happen with (x offset = 0) and (y offset = calcOffset)
recyclerView.scrollBy(0, offset);

The idea is simple: 1. We need to get the top coordinate of the recyclerview element; 2. We need to get the top coordinate of the view item that we want to scroll to the top; 3. At the end with the calculated offset we need to do

recyclerView.scrollBy(0, offset);

200 is just example hard coded integer value that you can use if the viewholder item doesn't exist, because that is possible as well.

来源：https://stackoverflow.com/questions/31235183/recyclerview-how-to-smooth-scroll-to-top-of-item-on-a-certain-position