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

的 iOS 消息应用程序中看到的 spring 行为。与消息一样，它会根据文本大小具有不同的单元格大小。我创建了一个自定义

UICollectionViewFlowLayout

，它确实将行为添加到

UICollectionView

中，但是在用户停止滚动后消息气泡继续轻微振荡。我尝试了任意数量的

length

、

damping

和

spring

值的组合，但振荡从未消失。

在阅读了其他堆栈问题后，我确实找到了这个评论

为了防止振荡，随着附加视图越来越接近其附加点，有必要以二次比例动态增加阻尼系数。 <

但我不太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

只需 2 个步骤即可修复。

1. 为首字母缩写时的行为添加动作，以确保单元格的中心在动画过程中不会改变

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

2. 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，并在该方法中删除/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，如果有改变阻尼的方法来修复，很想听听！