我正在寻找一种方法来滚动RecyclerView,以显示选中的项目在顶部。

在一个ListView中,我能够通过使用scrollTo(x,y)来做到这一点,并获得需要居中的元素的顶部。

喜欢的东西:

@Override
public void onItemClick(View v, int pos){
    mylistView.scrollTo(0, v.getTop());
}

问题是RecyclerView在使用它的scrollTo方法时返回一个错误说

RecyclerView不支持滚动到绝对位置

我如何滚动一个RecyclerView把选定的项目放在视图的顶部?


当前回答

我所做的恢复滚动位置后刷新RecyclerView按钮点击:

if (linearLayoutManager != null) {

    index = linearLayoutManager.findFirstVisibleItemPosition();
    View v = linearLayoutManager.getChildAt(0);
    top = (v == null) ? 0 : (v.getTop() - linearLayoutManager.getPaddingTop());
    Log.d("TAG", "visible position " + " " + index);
}

else{
    index = 0;
}

linearLayoutManager = new LinearLayoutManager(getApplicationContext());
linearLayoutManager.scrollToPositionWithOffset(index, top);

在创建linearLayoutManager对象之前,从顶部获得第一个可见项的偏移量,并在实例化它之后,调用linearLayoutManager对象的scrollToPositionWithOffset。

其他回答

你只需要调用recyclerview. scrolltopposition (position)。这很好!

如果你想在适配器中调用它,只需让你的适配器拥有recyclerview的实例或包含recyclerview的活动或片段,然后在它们中实现getRecyclerview()方法。

我希望它能帮助你。

调速器也一样

public class SmoothScrollLinearLayoutManager extends LinearLayoutManager {
private static final float MILLISECONDS_PER_INCH = 110f;
private Context mContext;

public SmoothScrollLinearLayoutManager(Context context,int orientation, boolean reverseLayout) {
    super(context,orientation,reverseLayout);
    mContext = context;
}

@Override
public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state,
                                   int position) {
    RecyclerView.SmoothScroller smoothScroller = new TopSnappedSmoothScroller(recyclerView.getContext()){
        //This controls the direction in which smoothScroll looks for your view
        @Override
        public PointF computeScrollVectorForPosition(int targetPosition) {
            return new PointF(0, 1);
        }

        //This returns the milliseconds it takes to scroll one pixel.
        @Override
        protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
            return MILLISECONDS_PER_INCH / displayMetrics.densityDpi;
        }
    };
    smoothScroller.setTargetPosition(position);
    startSmoothScroll(smoothScroller);
}


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

    }

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

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

我可以在这里添加的是如何使它与DiffUtil和ListAdapter一起工作

你可能会注意到调用recyclerView. scrolltopposition (pos)或(recyclerView. scrolltopposition)。layoutManager作为LinearLayoutManager)。如果在adapter.submitList后直接调用scrollToPositionWithOffset(pos, offset)将不起作用。这是因为differ在后台线程中查找更改,然后异步地将更改通知适配器。在一个SO上,我看到了几个错误的答案和不必要的延迟等来解决这个问题。

为了正确地处理这种情况,submitList有一个回调函数,在应用更改时调用它。

因此,在这种情况下,正确的kotlin实现是:

//memorise target item here and a scroll offset if needed
adapter.submitList(items) { 
    val pos = /* here you may find a new position of the item or just use just a static position. It depends on your case */
    recyclerView.scrollToPosition(pos) 
}
//or
adapter.submitList(items) { recyclerView.smoothScrollToPosition(pos) }
//or etc
adapter.submitList(items) { (recyclerView.layoutManager as LinearLayoutManager).scrollToPositionWithOffset(pos, offset) }

我使用下面的代码将一个项目(thisView)平滑滚动到顶部。 它也适用于GridLayoutManager不同高度的视图:

View firstView = mRecyclerView.getChildAt(0);
int toY = firstView.getTop();
int firstPosition = mRecyclerView.getChildAdapterPosition(firstView);
View thisView = mRecyclerView.getChildAt(thisPosition - firstPosition);
int fromY = thisView.getTop();

mRecyclerView.smoothScrollBy(0, fromY - toY);

似乎能快速解决问题。

请注意,如果scrolltopposition不工作,请注意您的RecyclerView是在一个NestedScrollView;参考这篇文章