Answers:
RecyclerView被设计为可扩展的，因此无需为了执行滚动而将其子类化LayoutManager（如droidev建议的那样）。
相反，只需创建一个SmoothScroller首选项SNAP_TO_START：
RecyclerView.SmoothScroller smoothScroller = new LinearSmoothScroller(context) {
@Override protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
};
现在，您设置要滚动到的位置：
smoothScroller.setTargetPosition(position);并将该SmoothScroller传递给LayoutManager：
layoutManager.startSmoothScroll(smoothScroller);为此，您必须创建一个自定义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;
}
}
}
将此用于您的RecyclerView并调用smoothScrollToPosition。
例如：
recyclerView.setLayoutManager(new LinearLayoutManagerWithSmoothScroller(context));
recyclerView.smoothScrollToPosition(position);
这将滚动到指定位置的RecyclerView项的顶部。
希望这可以帮助。
smoothScrollToPosition。为什么可能会出现此问题？谢谢。
这是我在Kotlin中编写的扩展功能，可用于（基于@Paul Woitaschek的回答）：RecyclerView
fun RecyclerView.smoothSnapToPosition(position: Int, snapMode: Int = LinearSmoothScroller.SNAP_TO_START) {
val smoothScroller = object : LinearSmoothScroller(this.context) {
override fun getVerticalSnapPreference(): Int = snapMode
override fun getHorizontalSnapPreference(): Int = snapMode
}
smoothScroller.targetPosition = position
layoutManager?.startSmoothScroll(smoothScroller)
}
像这样使用它：
myRecyclerView.smoothSnapToPosition(itemPosition)覆盖LinearSmoothScroller中的calculateDyToMakeVisible / calculateDxToMakeVisible函数以实现偏移的Y / X位置
override fun calculateDyToMakeVisible(view: View, snapPreference: Int): Int {
return super.calculateDyToMakeVisible(view, snapPreference) - ConvertUtils.dp2px(10f)
}
我发现滚动a的最简单方法RecyclerView如下：
// 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);
谢谢@droidev提供的解决方案。如果有人在寻找Kotlin解决方案，请参考以下内容：
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
}
}
}CustomLinearLayout.kt：
class CustomLayoutManager(private val context: Context, layoutDirection: Int):
LinearLayoutManager(context, layoutDirection, false) {
companion object {
// This determines how smooth the scrolling will be
private
const val MILLISECONDS_PER_INCH = 300f
}
override fun smoothScrollToPosition(recyclerView: RecyclerView, state: RecyclerView.State, position: Int) {
val smoothScroller: LinearSmoothScroller = object: LinearSmoothScroller(context) {
fun dp2px(dpValue: Float): Int {
val scale = context.resources.displayMetrics.density
return (dpValue * scale + 0.5f).toInt()
}
// change this and the return super type to "calculateDyToMakeVisible" if the layout direction is set to VERTICAL
override fun calculateDxToMakeVisible(view: View ? , snapPreference : Int): Int {
return super.calculateDxToMakeVisible(view, SNAP_TO_END) - dp2px(50f)
}
//This controls the direction in which smoothScroll looks for your view
override fun computeScrollVectorForPosition(targetPosition: Int): PointF ? {
return this @CustomLayoutManager.computeScrollVectorForPosition(targetPosition)
}
//This returns the milliseconds it takes to scroll one pixel.
override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
return MILLISECONDS_PER_INCH / displayMetrics.densityDpi
}
}
smoothScroller.targetPosition = position
startSmoothScroll(smoothScroller)
}
}注意：上面的示例设置为“水平”方向，可以在初始化期间传递“垂直/水平”。
如果将方向设置为“ 垂直”，则应将“ calculateDxToMakeVisible ” 更改为“ calculateDyToMakeVisible ”（还要注意超类型调用返回值）
活动/Fragment.kt：
...
smoothScrollerLayoutManager = CustomLayoutManager(context, LinearLayoutManager.HORIZONTAL)
recyclerView.layoutManager = smoothScrollerLayoutManager
.
.
.
fun onClick() {
// targetPosition passed from the adapter to activity/fragment
recyclerView.smoothScrollToPosition(targetPosition)
}@droidev方法可能是正确的方法，但是我只想发布一些不同的东西，它基本上完成了相同的工作，并且不需要扩展LayoutManager。
此处的注释 -如果您的项目（要滚动到列表顶部的项目）在屏幕上可见，而您只想自动将其滚动到顶部，这将很好地工作。当列表中的最后一个项目执行某些操作时会很有用，该操作会在同一列表中添加新项目，并且您希望用户将注意力集中在新添加的项目上：
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);这个想法很简单：1.我们需要获取recyclerview元素的最高坐标；2.我们需要获取要滚动到顶部的视图项的顶部坐标；3.最后，我们需要计算偏移量
recyclerView.scrollBy(0, offset);200仅是示例硬编码整数值，如果不存在viewholder项，则可以使用它，因为这也是可能的。
我想更全面地解决滚动持续时间的问题，如果您选择任何较早的答案，实际上会根据从当前位置到达目标位置所需的滚动量而发生巨大变化（并且是无法接受的）。
为了获得一致的滚动持续时间，速度（像素/毫秒）必须考虑每个单独项目的大小-并且当项目为非标准尺寸时，则会增加全新的复杂性。
这可能就是为什么RecyclerView开发人员将太过硬的篮子部署到平滑滚动这一至关重要的方面的原因。
假设您想要一个半均匀的滚动持续时间，并且您的列表包含半均匀的项目，那么您将需要这样的东西。
/** Smoothly scroll to specified position allowing for interval specification. <br>
* Note crude deceleration towards end of scroll
* @param rv Your RecyclerView
* @param toPos Position to scroll to
* @param duration Approximate desired duration of scroll (ms)
* @throws IllegalArgumentException */
private static void smoothScroll(RecyclerView rv, int toPos, int duration) throws IllegalArgumentException {
int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000; // See androidx.recyclerview.widget.LinearSmoothScroller
int itemHeight = rv.getChildAt(0).getHeight(); // Height of first visible view! NB: ViewGroup method!
itemHeight = itemHeight + 33; // Example pixel Adjustment for decoration?
int fvPos = ((LinearLayoutManager)rv.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
int i = Math.abs((fvPos - toPos) * itemHeight);
if (i == 0) { i = (int) Math.abs(rv.getChildAt(0).getY()); }
final int totalPix = i; // Best guess: Total number of pixels to scroll
RecyclerView.SmoothScroller smoothScroller = new LinearSmoothScroller(rv.getContext()) {
@Override protected int getVerticalSnapPreference() {
return LinearSmoothScroller.SNAP_TO_START;
}
@Override protected int calculateTimeForScrolling(int dx) {
int ms = (int) ( duration * dx / (float)totalPix );
// Now double the interval for the last fling.
if (dx < TARGET_SEEK_SCROLL_DISTANCE_PX ) { ms = ms*2; } // Crude deceleration!
//lg(format("For dx=%d we allot %dms", dx, ms));
return ms;
}
};
//lg(format("Total pixels from = %d to %d = %d [ itemHeight=%dpix ]", fvPos, toPos, totalPix, itemHeight));
smoothScroller.setTargetPosition(toPos);
rv.getLayoutManager().startSmoothScroll(smoothScroller);
}PS：我诅咒有一天我开始不加选择地将ListView转换为RecyclerView。
protected int getHorizontalSnapPreference() { return LinearSmoothScroller.SNAP_TO_START; }。此外，我必须实现抽象方法public PointF computeScrollVectorForPosition(int targetPosition) { return layoutManager.computeScrollVectorForPosition(targetPosition); }。