[英]From-To Page Changed Listener in PagerSnapHelper
I'm using PagerSnapHelper
in a horizontal RecyclerView
to achieve a view pager like behaviour.我在水平
RecyclerView
中使用PagerSnapHelper
来实现类似视图寻呼机的行为。
final PagerSnapHelper pagerSnapHelper = new PagerSnapHelper(); pagerSnapHelper.attachToRecyclerView(recyclerView);
It works great, but I want to be able to get callbacks for when the user changes the page in either direction.它工作得很好,但我希望能够在用户向任一方向更改页面时获得回调。 So something like,
onSwipeLeft
/ onSwipeRight
callbacks.所以类似于
onSwipeLeft
/ onSwipeRight
回调。
I tried using findTargetSnapPosition
in PagerSnapHelper
, but that only gives me the targetIndex
and not the current index.我尝试在
PagerSnapHelper
findTargetSnapPosition
但这只给我targetIndex
而不是当前索引。 I tried something like this, but it doesn't really work all the time.我试过这样的东西,但它并不总是有效。
@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;
}
Is there a better way to achieve this which always works?有没有更好的方法来实现这个总是有效的? Thanks!
谢谢!
Update 2更新 2
!! !! Important note !!
重要的提示 !!
If you programmatically call scrollTo()
and use the SnapPagerScrollListener
with ON_SETTLED
, onScrollStateChanged
won't get called.如果您以编程方式调用
scrollTo()
并将SnapPagerScrollListener
与ON_SETTLED
一起使用,则不会调用onScrollStateChanged
。 So the old snap position does not get updated.所以旧的捕捉位置不会得到更新。 WIP, will update the class as soon as I fix it.
WIP,我会在修复后立即更新课程。
Update更新
The original class had some issues with notifying on first layout.原始类在第一个布局上通知时存在一些问题。 Now it fires only the first time the item position changes from
RecyclerView.NO_POSITION
to something else.现在它仅在项目位置第一次从
RecyclerView.NO_POSITION
更改为其他位置时触发。
To further extend to ignore/fire only on user gestures, so non programmatic calls to scrollTo()
, note that onScrolled()
gets triggered with dx == 0 and dy == 0
in case of a programmatic call.为了进一步扩展到仅在用户手势上忽略/触发,因此对
scrollTo()
的非编程调用,请注意,在编程调用的情况下, onScrolled()
会被dx == 0 and dy == 0
触发。
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;
}
}
Usage:用法:
Just add an instance of SnapPagerScrollListener to your RecyclerView只需将 SnapPagerScrollListener 的实例添加到您的 RecyclerView
your_recycler_view.addOnScrollListener(new SnapPagerScrollListener(your_snap_helper, SnapPagerScrollListener.ON_SCROLL/ON_SETTLED, true/false, your_on_changed_listener));
The Type
property is for defining when the callbacks should be triggered. Type
属性用于定义何时触发回调。
SCROLL_STATE_IDLE
. SCROLL_STATE_IDLE
后的回调。 I use the mode for only firing API calls when the scroll has settled.
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