从 UICollectionView 中的 UIAttachmentBehavior 中删除振荡

Question

我正在尝试重新创建您在我的UICollectionView 中的 iOS 消息应用程序中看到的弹簧行为。与消息一样，它将根据文本大小具有各种单元格大小。我创建了一个自定义UICollectionViewFlowLayout，它确实将行为添加到UICollectionView，但是在用户停止滚动后，消息气泡会继续轻微振荡。我在length、damping 和spring 值中尝试了任意数量的组合，但振荡永远不会消失。

在阅读了一些其他堆栈问题后，我确实找到了这条评论

为了防止振荡，随着附加视图越来越接近它们的附加点，有必要在二次尺度上动态增加阻尼因子。

但是我不确定从哪里开始在我目前拥有的东西上实施类似的东西。任何帮助或指导将不胜感激。

下面是我在 UICollectionViewFlowLayout 上创建当前效果的代码。

- (void) prepareLayout {
[super prepareLayout];

CGRect originalRect = (CGRect){.origin = self.collectionView.bounds.origin, .size = self.collectionView.frame.size};
CGRect visibleRect = CGRectInset(originalRect, -50, -50);

NSArray *itemsInVisibleRectArray = [super layoutAttributesForElementsInRect:visibleRect];
NSSet *itemsIndexPathsInVisibleRectSet = [NSSet setWithArray:[itemsInVisibleRectArray valueForKey:@"indexPath"]];


NSPredicate *predicate = [NSPredicate predicateWithBlock:^BOOL(UIAttachmentBehavior *behaviour, NSDictionary *bindings) {
    BOOL currentlyVisible = [itemsIndexPathsInVisibleRectSet member:[[[behaviour items] firstObject] indexPath]] != nil;
    return !currentlyVisible;
}];
NSArray *noLongerVisibleBehaviours = [self.animator.behaviors filteredArrayUsingPredicate:predicate];

[noLongerVisibleBehaviours enumerateObjectsUsingBlock:^(id obj, NSUInteger index, BOOL *stop) {
    [self.animator removeBehavior:obj];
    [self.visibleIndexPathsSet removeObject:[[[obj items] firstObject] indexPath]];
}];


NSPredicate *newPredicate = [NSPredicate predicateWithBlock:^BOOL(UICollectionViewLayoutAttributes *item, NSDictionary *bindings) {
    BOOL currentlyVisible = [self.visibleIndexPathsSet member:item.indexPath] != nil;
    return !currentlyVisible;
}];
NSArray *newlyVisibleItems = [itemsInVisibleRectArray filteredArrayUsingPredicate:newPredicate];
CGPoint touchLocation = [self.collectionView.panGestureRecognizer locationInView:self.collectionView];



[newlyVisibleItems enumerateObjectsUsingBlock:^(UICollectionViewLayoutAttributes *item, NSUInteger idx, BOOL *stop) {
    CGPoint center = item.center;
    UIAttachmentBehavior *springBehaviour = [[UIAttachmentBehavior alloc] initWithItem:item attachedToAnchor:center];

    springBehaviour.length = 0.1f;
    springBehaviour.damping = 3.0f;
    springBehaviour.frequency = 2.8f;

    if (!CGPointEqualToPoint(CGPointZero, touchLocation)) {
        CGFloat yDistanceFromTouch = fabs(touchLocation.y - springBehaviour.anchorPoint.y);
        CGFloat xDistanceFromTouch = fabs(touchLocation.x - springBehaviour.anchorPoint.x);
        CGFloat scrollResistance = (yDistanceFromTouch + xDistanceFromTouch) / 1500.0f;

        if (self.latestDelta < 0) {
            center.y += MAX(self.latestDelta, self.latestDelta*scrollResistance);
        }
        else {
            center.y += MIN(self.latestDelta, self.latestDelta*scrollResistance);
        }
        item.center = center;
    }

    [self.animator addBehavior:springBehaviour];
    [self.visibleIndexPathsSet addObject:item.indexPath];
}];
}

Answer 1

您可以通过 2 个步骤来修复它。
1. 为behavior添加动作，以确保在动画期间单元格的中心不会改变

springBehaviour.action = ^{
            CGPoint itemCenter = item.center;
            itemCenter.x = center.x;
            item.center = itemCenter;
        };

1. 删除/重新添加collectionview 停止滚动时的行为。为此，您需要实现一个滚动视图委托方法，并在此方法中删除/重新添加行为。

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView { ZZHCollectionFlowLayout *flowLayout = self.collectionView.collectionViewLayout; if ([flowLayout isKindOfClass:[ZZHCollectionFlowLayout class]]) { [flowLayout removeAnimationBehavior]; } else { // Your NSAssertionHandler } } - (void)removeAnimationBehavior { NSArray *behaviors = self.dynamicAnimator.behaviors; [self.dynamicAnimator removeAllBehaviors]; for (UIDynamicBehavior *obj in behaviors) { [self.dynamicAnimator addBehavior:obj]; } }

顺便说一句，如果有办法改变阻尼来修复，想听听！