我一直试图让smoothScrollToPositionFromTop（）工作，但它并不总是滚动到正确的位置。
我在一个布局中有一个ListView（有10个项目），旁边有10个按钮，所以我可以滚动到列表中的每个项目。通常当我向后或向前滚动一个位置时它工作正常，但是当我尝试向后或向前滚动超过3个位置时，ListView并不完全在所选位置结束。当它失败时，通常会关闭0.5到1.5个项目，当滚动失败时它不能真正预测。
我还检查了smoothScrollToPosition after notifyDataSetChanged not working in android，但此修复程序对我不起作用，我不会更改任何数据。
我真的想自动滚动到所选的列表项，但不是我无法弄清楚如何。有没有人以前遇到过这个问题并且知道如何修复它？
答案 0 :(得分：50)
这是一个已知的错误。见https://code.google.com/p/android/issues/detail?id=36062
但是，我实施了此解决方法，处理可能发生的所有边缘情况：
首先调用smothScrollToPositionFromTop(position)，然后在滚动完成后，调用setSelection(position)。后一个调用通过直接跳到所需位置来纠正不完整的滚动。这样做，用户仍然会感觉它正在动画滚动到此位置。
我在两个辅助方法中实现了这个解决方法：
<强> smoothScrollToPositionFromTop（）
public static void smoothScrollToPositionFromTop(final AbsListView view, final int position) {
View child = getChildAtPosition(view, position);
// There's no need to scroll if child is already at top or view is already scrolled to its end
if ((child != null) && ((child.getTop() == 0) || ((child.getTop() > 0) && !view.canScrollVertically(1)))) {
return;
}
view.setOnScrollListener(new AbsListView.OnScrollListener() {
@Override
public void onScrollStateChanged(final AbsListView view, final int scrollState) {
if (scrollState == SCROLL_STATE_IDLE) {
view.setOnScrollListener(null);
// Fix for scrolling bug
new Handler().post(new Runnable() {
@Override
public void run() {
view.setSelection(position);
}
});
}
}
@Override
public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount,
final int totalItemCount) { }
});
// Perform scrolling to position
new Handler().post(new Runnable() {
@Override
public void run() {
view.smoothScrollToPositionFromTop(position, 0);
}
});
}
<强> getChildAtPosition（）
public static View getChildAtPosition(final AdapterView view, final int position) {
final int index = position - view.getFirstVisiblePosition();
if ((index >= 0) && (index < view.getChildCount())) {
return view.getChildAt(index);
} else {
return null;
}
}
答案 1 :(得分：3)
以下是解决方案的实现。
void smoothScrollToPositionFromTopWithBugWorkAround(final AbsListView listView,
final int position,
final int offset,
final int duration){
//the bug workaround involves listening to when it has finished scrolling, and then
//firing a new scroll to the same position.
//the bug is the case that sometimes smooth Scroll To Position sort of misses its intended position.
//more info here : https://code.google.com/p/android/issues/detail?id=36062
listView.smoothScrollToPositionFromTop(position, offset, duration);
listView.setOnScrollListener(new OnScrollListener() {
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if(scrollState==OnScrollListener.SCROLL_STATE_IDLE){
listView.setOnScrollListener(null);
listView.smoothScrollToPositionFromTop(position, offset, duration);
}
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
}
});
}
答案 2 :(得分：0)
正如四楼google issuetracker页面所述：https://issuetracker.google.com/issues/36952786
前面给出的解决方法，“现在的解决方法是在启动滚动时侦听SCROLL_STATE_IDLE，并将smoothScrollToPositionFromTop再次侦听到相同的位置。”也不会一直有效。
实际上，使用SCROLL_STATE_IDLE调用onScrollStateChanged并不一定意味着滚动已完成。因此，它仍然无法保证Listview每次都滚动到正确的位置，尤其是当列表项视图不是全部在同一高度时。
经过研究，我发现另一种方法可以正确合理地工作。众所周知，Listview提供了一个方法scrollListBy（int y），它使我们能够立即向上滚动Listview y像素。然后，在计时器的帮助下，我们可以自己平滑地正确滚动列表。
我们需要做的第一件事是计算每个列表项视图的高度，包括屏幕外的视图。由于之前已知列表数据和子视图的类型，因此计算每个列表项视图的高度是可行的。因此，给定目标位置以平滑滚动，我们可以计算其在y方向上的滚动距离。此外，应在完成ListView初始化后进行计算。
第二件事是组合一个计时器和scrollListBy（int）方法。实际上我们可以使用android.os.Handler的sendEmptyMessageDelayed（）方法。因此，解决方案可以是：
/**
* Created by CaiHaozhong on 2017/9/29.
*/
public class ListViewSmoothScroller {
private final static int MSG_ACTION_SCROLL = 1;
private final static int MSG_ACTION_ADJUST = 2;
private ListView mListView = null;
/* The accumulated height of each list item view */
protected int[] mItemAccumulateHeight = null;
protected int mTimeStep = 20;
protected int mHeaderViewHeight;
private int mPos;
private Method mTrackMotionScrollMethod = null;
protected int mScrollUnit = 0;
protected int mTotalMove = 0;
protected int mTargetScrollDis = 0;
private Handler mMainHandler = new Handler(Looper.getMainLooper()){
public void handleMessage(Message msg) {
int what = msg.what;
switch (what){
case MSG_ACTION_SCROLL: {
int scrollDis = mScrollUnit;
if(mTotalMove + mScrollUnit > mTargetScrollDis){
scrollDis = mTargetScrollDis - mTotalMove;
}
if(Build.VERSION.SDK_INT >= 19) {
mListView.scrollListBy(scrollDis);
}
else{
if(mTrackMotionScrollMethod != null){
try {
mTrackMotionScrollMethod.invoke(mListView, -scrollDis, -scrollDis);
}catch(Exception ex){
ex.printStackTrace();
}
}
}
mTotalMove += scrollDis;
if(mTotalMove < mTargetScrollDis){
mMainHandler.sendEmptyMessageDelayed(MSG_ACTION_SCROLL, mTimeStep);
}else {
mMainHandler.sendEmptyMessageDelayed(MSG_ACTION_ADJUST, mTimeStep);
}
break;
}
case MSG_ACTION_ADJUST: {
mListView.setSelection(mPos);
break;
}
}
}
};
public ListViewSmoothScroller(Context context, ListView listView){
mListView = listView;
mScrollUnit = Tools.dip2px(context, 60);
mPos = -1;
try {
mTrackMotionScrollMethod = AbsListView.class.getDeclaredMethod("trackMotionScroll", int.class, int.class);
}catch (NoSuchMethodException ex){
ex.printStackTrace();
mTrackMotionScrollMethod = null;
}
if(mTrackMotionScrollMethod != null){
mTrackMotionScrollMethod.setAccessible(true);
}
}
/* scroll to a target position smoothly */
public void smoothScrollToPosition(int pos){
if(mListView == null)
return;
if(mItemAccumulateHeight == null || pos >= mItemAccumulateHeight.length){
return ;
}
mPos = pos;
mTargetScrollDis = mItemAccumulateHeight[pos];
mMainHandler.sendEmptyMessage(MSG_ACTION_SCROLL);
}
/* call after initializing ListView */
public void doMeasureOnLayoutChange(){
if(mListView == null){
return;
}
int headerCount = mListView.getHeaderViewsCount();
/* if no list item */
if(mListView.getChildCount() < headerCount + 1){
return ;
}
mHeaderViewHeight = 0;
for(int i = 0; i < headerCount; i++){
mHeaderViewHeight += mListView.getChildAt(i).getHeight();
}
View firstListItemView = mListView.getChildAt(headerCount);
computeAccumulateHeight(firstListItemView);
}
/* calculate the accumulated height of each list item */
protected void computeAccumulateHeight(View firstListItemView){
int len = listdata.size();// count of list item
mItemAccumulateHeight = new int[len + 2];
mItemAccumulateHeight[0] = 0;
mItemAccumulateHeight[1] = mHeaderViewHeight;
int currentHeight = mHeaderViewHeight;
for(int i = 2; i < len + 2; i++){
currentHeight += getItemHeight(firstListItemView);
mItemAccumulateHeight[i] = currentHeight;
}
}
/* get height of a list item. You may need to pass the listdata of the list item as parameter*/
protected int getItemHeight(View firstListItemView){
// Considering the structure of listitem View and the list data in order to calculate the height.
}
}
在完成ListView的初始化之后，我们调用doMeasureOnLayoutChange（）方法。之后，我们可以通过smoothScrollToPosition（int pos）方法滚动ListView。我们可以像这样调用doMeasureOnLayoutChange（）方法：
mListAdapter.notifyDataSetChanged();
mListView.post(new Runnable() {
@Override
public void run() {
mListViewSmoothScroller.doMeasureOnLayoutChange();
}
});
最后，我们的ListView可以顺利滚动到目标位置，更重要的是，正确滚动。
答案 3 :(得分：0)
尝试将高度从“ wrap_content”更改为“ match_parent”
<RecyclerView
android: layout_height="match_parent"
... >
smothScrollToPosition(0) // works ok
答案 4 :(得分：0)
这是Lars Blumberg在Kotlin的回答，包括dira的评论，对我有用。
private fun smoothScrollToPositionFromTop(listView: AbsListView, position: Int, offset: Int) {
listView.setOnScrollListener(object : AbsListView.OnScrollListener {
override fun onScroll(
view: AbsListView?,
firstVisibleItem: Int,
visibleItemCount: Int,
totalItemCount: Int
) { }
override fun onScrollStateChanged(view: AbsListView?, scrollState: Int) {
view?.setOnScrollListener(null)
// Fix for scrolling bug.
if (scrollState == SCROLL_STATE_IDLE) {
Handler(Looper.getMainLooper()).post {
listView.setSelectionFromTop(position, offset)
}
}
}
})
// Perform scrolling to position
Handler(Looper.getMainLooper()).post {
listView.smoothScrollToPositionFromTop(position, offset)
}
}