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
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;
}
}
}
其他回答
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。
只需简单地调用这个方法:
((LinearLayoutManager)recyclerView.getLayoutManager()).scrollToPositionWithOffset(yourItemPosition,0);
而不是:
recyclerView.scrollToPosition(yourItemPosition);
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
如果你正在使用LinearLayoutManager或交错的GridLayoutManager，它们都有一个scrollToPositionWithOffset方法，该方法既取位置，也取项目从RecyclerView开始的偏移量，这似乎可以完成你所需要的(将偏移量设置为0应该与顶部对齐)。
例如:
//Scroll item 2 to 20 pixels from the top
linearLayoutManager.scrollToPositionWithOffset(2, 20);
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。
