我一直在尝试让 smoothScrollToPositionFromTop() 工作，但它并不总是滚动到正确的位置。
我的布局中有一个 ListView（有 10 个项目），侧面有 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，但通常当我尝试向后或向前滚动超过 3 个位置时，ListView 不会完全在所选位置结束。当它失败时，它通常会关闭 0,5 到 1,5 个项目，并且当滚动失败时它是不可预测的。
在 notifyDataSetChanged not working in android 之后，我还检查了smoothScrollToPosition ，但是这个修复对我不起作用，我没有更改任何数据。
我真的很想自动滚动到选定的列表项，但不是我不知道怎么做。以前有没有人遇到过这个问题并且知道如何解决它？
这是一个已知的错误。请参阅https://code.google.com/p/android/issues/detail?id=36062
但是，我实现了这个解决方法来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转到所需位置来纠正不完整的滚动。这样做，用户仍然会觉得它正在被动画滚动到这个位置。
我在两个辅助方法中实现了这个解决方法：
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);
}
});
}
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;
}
}
这是解决方案的实现。
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) {
}
});
}
如四楼google issuetracker页面中提到的：<a href="https://issuetracker.google.com/issues/36952786" rel="nofollow noreferrer">https://issuetracker.google.com/issues /36952786
前面给出的解决方法，“现在的解决方法是在开始滚动时侦听 SCROLL_STATE_IDLE，并再次将 smoothScrollToPositionFromTop 到相同的位置。” 也不总是有效。
实际上，使用 SCROLL_STATE_IDLE 调用 onScrollStateChanged 并不一定意味着滚动已经完成。结果，它仍然不能保证 Listview 每次都滚动到正确的位置，尤其是当列表项视图不是都在同一高度时。
经过研究，我发现了另一种完全正确且合理的方法。众所周知，Listview 提供了一个方法 scrollListBy(int y)，它使我们能够立即将 Listview 向上滚动 y 个像素。然后，在计时器的帮助下，我们可以自己流畅、正确地滚动列表。
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。由于之前已经知道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，给定一个平滑滚动到的目标位置，我们可以计算它在 y 方向上的滚动距离。另外，计算应该在ListView初始化完成后进行。
第二件事是将计时器和 scrollListBy(int) 方法结合起来。其实我们可以使用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.
}
}
完成初始化 ListView 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 可以平滑地滚动到目标位置，更重要的是，正确地滚动。
尝试将高度从“wrap_content”更改为“match_parent”
<RecyclerView
android: layout_height="match_parent"
... >
smothScrollToPosition(0) // works ok
这是 Kotlin 中的 Lars Blumberg 回答，包括 dira 的评论，它对我有用。
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)
}
}