[英]From-To Page Changed Listener in PagerSnapHelper
我在水平RecyclerView
中使用PagerSnapHelper
來實現類似視圖尋呼機的行為。
final PagerSnapHelper pagerSnapHelper = new PagerSnapHelper(); pagerSnapHelper.attachToRecyclerView(recyclerView);
它工作得很好,但我希望能夠在用戶向任一方向更改頁面時獲得回調。 所以類似於onSwipeLeft
/ onSwipeRight
回調。
我嘗試在PagerSnapHelper
findTargetSnapPosition
但這只給我targetIndex
而不是當前索引。 我試過這樣的東西,但它並不總是有效。
@Override
public int findTargetSnapPosition(RecyclerView.LayoutManager layoutManager, int velocityX, int velocityY) {
final int targetPos = super.findTargetSnapPosition(layoutManager, velocityX, velocityY);
final View currentView = findSnapView(layoutManager);
final int currentPos = layoutManager.getPosition(currentView);
if (currentPos < targetPos) {
callback.onSwipeRight();
} else if (currentPos > targetPos) {
callback.onSwipeLeft();
}
return targetPos;
}
有沒有更好的方法來實現這個總是有效的? 謝謝!
更新 2
!! 重要的提示 !!
如果您以編程方式調用scrollTo()
並將SnapPagerScrollListener
與ON_SETTLED
一起使用,則不會調用onScrollStateChanged
。 所以舊的捕捉位置不會得到更新。 WIP,我會在修復后立即更新課程。
更新
原始類在第一個布局上通知時存在一些問題。 現在它僅在項目位置第一次從RecyclerView.NO_POSITION
更改為其他位置時觸發。
為了進一步擴展到僅在用戶手勢上忽略/觸發,因此對scrollTo()
的非編程調用,請注意,在編程調用的情況下, onScrolled()
會被dx == 0 and dy == 0
觸發。
public class SnapPagerScrollListener extends RecyclerView.OnScrollListener {
// Constants
public static final int ON_SCROLL = 0;
public static final int ON_SETTLED = 1;
@IntDef({ON_SCROLL, ON_SETTLED})
public @interface Type {
}
public interface OnChangeListener {
void onSnapped(int position);
}
// Properties
private final PagerSnapHelper snapHelper;
private final int type;
private final boolean notifyOnInit;
private final OnChangeListener listener;
private int snapPosition;
// Constructor
public SnapPagerScrollListener(PagerSnapHelper snapHelper, @Type int type, boolean notifyOnInit, OnChangeListener listener) {
this.snapHelper = snapHelper;
this.type = type;
this.notifyOnInit = notifyOnInit;
this.listener = listener;
this.snapPosition = RecyclerView.NO_POSITION;
}
// Methods
@Override
public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if ((type == ON_SCROLL) || !hasItemPosition()) {
notifyListenerIfNeeded(getSnapPosition(recyclerView));
}
}
@Override
public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (type == ON_SETTLED && newState == RecyclerView.SCROLL_STATE_IDLE) {
notifyListenerIfNeeded(getSnapPosition(recyclerView));
}
}
private int getSnapPosition(RecyclerView recyclerView) {
RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
if (layoutManager == null) {
return RecyclerView.NO_POSITION;
}
View snapView = snapHelper.findSnapView(layoutManager);
if (snapView == null) {
return RecyclerView.NO_POSITION;
}
return layoutManager.getPosition(snapView);
}
private void notifyListenerIfNeeded(int newSnapPosition) {
if (snapPosition != newSnapPosition) {
if (notifyOnInit && !hasItemPosition()) {
listener.onSnapped(newSnapPosition);
} else if (hasItemPosition()) {
listener.onSnapped(newSnapPosition);
}
snapPosition = newSnapPosition;
}
}
private boolean hasItemPosition() {
return snapPosition != RecyclerView.NO_POSITION;
}
}
用法:
只需將 SnapPagerScrollListener 的實例添加到您的 RecyclerView
your_recycler_view.addOnScrollListener(new SnapPagerScrollListener(your_snap_helper, SnapPagerScrollListener.ON_SCROLL/ON_SETTLED, true/false, your_on_changed_listener));
Type
屬性用於定義何時觸發回調。
SCROLL_STATE_IDLE
后的回調。 我使用該模式僅在滾動穩定后觸發 API 調用。
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