Question

我在水平PagerSnapHelper中使用RecyclerView来实现类似行为的视图寻呼机。

final PagerSnapHelper pagerSnapHelper = new PagerSnapHelper(); pagerSnapHelper.attachToRecyclerView(recyclerView);

它很好用，但是我希望能够在用户向任一方向更改页面时获得回调。类似于onSwipeLeft / onSwipeRight回调。

我尝试在findTargetSnapPosition中使用PagerSnapHelper，但这只给了我targetIndex，而不是当前索引。我尝试过类似的方法，但实际上并非一直如此。

@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;
}

是否有更好的方法来实现始终有效的目标？谢谢！

Answer 1

更新

原始类在通知第一次布局时遇到一些问题。现在，它仅在项目位置从RecyclerView.NO_POSITION更改为其他位置时才触发。

要进一步扩展为仅对用户手势忽略/触发，以便对scrollTo()进行非编程调用，请注意，在进行编程调用的情况下，onScrolled()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;
    }
}

原始答案

由于没有构建方式，因此需要创建自己的自定义类。这个想法是监听RecyclerViews onScrolled()/onScrollStateChanged()方法，并在需要时通知您的回调。
接口方法有点重叠，我删除了onSwipeLeft/Right()方法。这只是为了演示。

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);

        void onSwipeRight();

        void onSwipeLeft();
    }

    // Properties
    private final PagerSnapHelper snapHelper;
    private final int type;
    private final boolean notifyOnFirstLayout;
    private final OnChangeListener listener;
    private int snapPosition;

    // Constructor
    public SnapPagerScrollListener(PagerSnapHelper snapHelper, @Type int type, boolean notifyOnFirstLayout, OnChangeListener listener) {
        this.snapHelper = snapHelper;
        this.type = type;
        this.notifyOnFirstLayout = notifyOnFirstLayout;
        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) || notifyOnFirstLayout) {
            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 (!isFirstLayout() || notifyOnFirstLayout) {
                listener.onSnapped(newSnapPosition);
            }

            if (!isFirstLayout()) {
                if (snapPosition > newSnapPosition) {
                    listener.onSwipeLeft();
                } else if (snapPosition < newSnapPosition) {
                    listener.onSwipeRight();
                }
            }

            snapPosition = newSnapPosition;
        }
    }

    private boolean isFirstLayout() {
        return snapPosition == RecyclerView.NO_POSITION;
    }
}

用法：
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));

根据{{1}}

的文档

如果在布局计算后可见项范围发生更改，则也会调用此回调。在这种情况下，dx和dy将为0。

我添加了额外的布尔值，以在布局计算后的第一时间获取/获取未通知的信息。

RecyclerView.onScrolled()属性用于定义何时应触发回调。

ON_SCROLL：用于在新视图/页面经过中间时立即通知回调
ON_SETTLED：用于在RecyclerViews状态为Type后通知回调。我使用此模式仅在滚动结束后触发API调用。

PagerSnapHelper中的从页面到页面更改的侦听器

1 个答案: