我已经试了一段时间来让smoothScrollToPositionFromTop()正常工作，但它并不能总是滚动到正确的位置。
我有一个带有10个按钮的布局中的ListView（具有10个项目），因此我可以滚动到列表中的每个项目。通常，当我向前或向后滚动一个位置时，它可以正常工作，但通常当我尝试向前或向后滚动超过3个位置时，ListView无法准确地停在所选的位置上。当它失败时，它通常会停留在0.5至1.5个项目处，而且滚动失败是不可预测的。
我还查看了 smoothScrollToPosition after notifyDataSetChanged not working in android，但这种解决方法对我没有用，而且我也没有改变任何数据。
我真的想自动滚动到所选的列表项，但我现在无法弄清楚如何实现。是否有人以前遇到过这个问题，并知道如何解决？
这是一个已知的 bug，参见 https://code.google.com/p/android/issues/detail?id=36062
然而，我实现了这个解决方法来处理可能出现的所有边缘情况：
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，用户仍然有一种被动画式地滚动到此位置的印象。
我在两个帮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;
}
}
View.canScrollVertically(int) 需要 API Level 14。你可以使用 ViewCompat.canScrollVertically(View, int) 来代替。 - jenzz
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) {
}
});
}
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。由于列表数据和子视图类型已知，因此可以计算每个列表项视图的高度。因此，给定一个平滑滚动到的目标位置，我们可以计算其在y方向上的滚动距离。此外，计算应在完成初始化ListView之后进行。
第二件事是将计时器和scrollListBy（int）方法结合起来。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.
}
}
在初始化我们的ListView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();
}
});
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Lars Blumberg在Kotlin中的答案，包括dira的评论，对我有效。
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)
}
}