我一直在复制2013 WWDC Session 217“探索iOS 7上的滚动视图”.我正在使用
Xcode 7 beta 2,而我的项目只有iOS 9.
我试图用UICollectionViewLayout使用一个UIDynamicAnimator,类似于会话217中提出的模拟Messages.app的感觉.我的UICollectionViewLayout是一个自定义的,由于某种原因,我的单元格似乎在我的项目中以循环运动反弹.
这是一个更加清晰的video的问题.
// Didn't write this code myself,but should be pretty simple to follow. @Goles
#import "VVSpringCollectionViewFlowLayout.h"
@interface VVSpringCollectionViewFlowLayout()
@property (nonatomic,strong) UIDynamicAnimator *animator;
@end
@implementation VVSpringCollectionViewFlowLayout
-(id)init {
if (self = [super init]) {
_springDamping = 0.5;
_springFrequency = 0.8;
_resistanceFactor = 500;
}
return self;
}
- (id)initWithCoder:(nonnull NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
if (self) {
_springDamping = 0.5;
_springFrequency = 0.8;
_resistanceFactor = 500;
}
return self;
}
-(void)prepareLayout {
[super prepareLayout];
if (!_animator) {
_animator = [[UIDynamicAnimator alloc] initWithCollectionViewLayout:self];
CGSize contentSize = [self collectionViewContentSize];
NSArray *items = [super layoutAttributesForElementsInRect:CGRectMake(0,contentSize.width,contentSize.height)];
for (UICollectionViewLayoutAttributes *item in items) {
UIAttachmentBehavior *spring = [[UIAttachmentBehavior alloc] initWithItem:item attachedToAnchor:item.center];
spring.length = 0;
spring.damping = self.springDamping;
spring.frequency = self.springFrequency;
[_animator addBehavior:spring];
}
}
}
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
return [_animator itemsInRect:rect];
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
return [_animator layoutAttributesForCellAtIndexPath:indexPath];
}
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
UIScrollView *scrollView = self.collectionView;
CGFloat scrollDelta = newBounds.origin.y - scrollView.bounds.origin.y;
CGPoint touchLocation = [scrollView.panGestureRecognizer locationInView:scrollView];
for (UIAttachmentBehavior *spring in _animator.behaviors) {
CGPoint anchorPoint = spring.anchorPoint;
CGFloat distanceFromTouch = fabs(touchLocation.y - anchorPoint.y);
CGFloat scrollResistance = distanceFromTouch / self.resistanceFactor;
id<UIDynamicItem> item = [spring.items firstObject];
CGPoint center = item.center;
if (scrollDelta > 0) {
center.y += MIN(scrollDelta,scrollDelta * scrollResistance);
}
item.center = center;
[_animator updateItemUsingCurrentState:item];
}
return NO;
}
@end
这可能导致这个循环议案呢？我只是改变我的UIAttachmentAttributes中心的Y轴属性.
center.y += MIN(scrollDelta,scrollDelta * scrollResistance);
我在这里缺少什么？ (在其他项目中尝试这种精确的布局,似乎工作).
编辑：
我上传了一个示例项目(删除),自定义集合视图布局类被称为VVSpringCollectionViewFlowLayout.m,没有太多的时间来看这个太多了,因为我最近在工作上做了很多工作.
当示例项目运行(Xcode 7 beta或更高版本)时,系统将提示您使用滑块,向右拖动可视化集合视图单元格.
解决方法
以下代码可以帮助您/指向正确的方向.它还有一些额外的东西 – 像清理不必要的动画师行为,如果不在视线中,跟踪触摸这样的动画师的行为.剥离了一个旧的项目,所以应该只是工作.包含演示创建视频的Github示例项目 –
https://github.com/serendipityapps/SpringyCollectionView
@interface VVSpringCollectionViewFlowLayout ()
@property (nonatomic,strong) UIDynamicAnimator *dynamicAnimator;
@property (nonatomic,strong) NSMutableSet *visibleIndexPathsSet;
@property (nonatomic,assign) CGFloat latestDelta;
@end
@implementation VVSpringCollectionViewFlowLayout
- (id)init {
if (self = [super init]) {
self.dynamicAnimator = [[UIDynamicAnimator alloc] initWithCollectionViewLayout:self];
self.visibleIndexPathsSet = [NSMutableSet set];
}
return self;
}
- (id)initWithCoder:(nonnull NSCoder *)aDecoder {
if (self = [super initWithCoder:aDecoder]) {
self.dynamicAnimator = [[UIDynamicAnimator alloc] initWithCollectionViewLayout:self];
self.visibleIndexPathsSet = [NSMutableSet set];
}
return self;
}
-(NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
return [self.dynamicAnimator itemsInRect:rect];
}
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
return [self.dynamicAnimator layoutAttributesForCellAtIndexPath:indexPath];
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
return [self.dynamicAnimator layoutAttributesForSupplementaryViewOfKind:kind atIndexPath:indexPath];
}
-(void)prepareLayout {
[super prepareLayout];
// Need to enlarge visible rect slightly to avoid flickering.
CGRect visibleRect = CGRectInset((CGRect){.origin = self.collectionView.bounds.origin,.size = self.collectionView.frame.size},-100,-100);
NSArray *itemsInVisibleRectArray = [super layoutAttributesForElementsInRect:visibleRect];
NSArray *cells = [itemsInVisibleRectArray filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(UICollectionViewLayoutAttributes *item,NSDictionary *bindings) {
return !item.representedElementKind;
}]];
NSSet *itemsIndexPathsInVisibleRectSet = [NSSet setWithArray:[cells valueForKey:@"indexPath"]];
// Remove any behavIoUrs that are no longer visible.
NSArray *noLongerVisibleBehavIoUrsCells = [self.dynamicAnimator.behaviors filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(UIAttachmentBehavior *behavIoUr,NSDictionary *bindings) {
UICollectionViewLayoutAttributes *item= (UICollectionViewLayoutAttributes*)[[behavIoUr items] firstObject];
if (!item.representedElementKind) {
BOOL currentlyVisible = [itemsIndexPathsInVisibleRectSet member:[item indexPath]] != nil;
return !currentlyVisible;
}
else {
return NO;
}
}]];
[noLongerVisibleBehavIoUrsCells enumerateObjectsUsingBlock:^(UIAttachmentBehavior *behavIoUr,NSUInteger index,BOOL *stop) {
UICollectionViewLayoutAttributes *item = (UICollectionViewLayoutAttributes*)[[behavIoUr items] firstObject];
[self.dynamicAnimator removeBehavior:behavIoUr];
[self.visibleIndexPathsSet removeObject:[item indexPath]];
}];
// Add any newly visible behavIoUrs.
CGPoint touchLocation = [self.collectionView.panGestureRecognizer locationInView:self.collectionView];
// A "newly visible" item is one that is in the itemsInVisibleRect(Set|Array) but not in the visibleIndexPathsSet
NSArray *newlyVisibleItems = [cells filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(UICollectionViewLayoutAttributes *item,NSDictionary *bindings) {
BOOL currentlyVisible = [self.visibleIndexPathsSet member:item.indexPath] != nil;
return !currentlyVisible;
}]];
[newlyVisibleItems enumerateObjectsUsingBlock:^(UICollectionViewLayoutAttributes *item,NSUInteger idx,BOOL *stop) {
CGPoint center = item.center;
UIAttachmentBehavior *springBehavIoUr = [[UIAttachmentBehavior alloc] initWithItem:item attachedToAnchor:center];
springBehavIoUr.length = 0.0f;
springBehavIoUr.damping = 0.8f;
springBehavIoUr.frequency = 1.0f;
// If our touchLocation is not (0,0),we'll need to adjust our item's center "in flight"
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.dynamicAnimator addBehavior:springBehavIoUr];
[self.visibleIndexPathsSet addObject:item.indexPath];
}];
}
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
UIScrollView *scrollView = self.collectionView;
CGFloat delta = newBounds.origin.y - scrollView.bounds.origin.y;
self.latestDelta = delta;
CGPoint touchLocation = [self.collectionView.panGestureRecognizer locationInView:self.collectionView];
__block UIDynamicAnimator *weakDynamicAnimator = self.dynamicAnimator;
[self.dynamicAnimator.behaviors enumerateObjectsUsingBlock:^(UIAttachmentBehavior *springBehavIoUr,BOOL *stop) {
CGFloat yDistanceFromTouch = fabs(touchLocation.y - springBehavIoUr.anchorPoint.y);
CGFloat xDistanceFromTouch = fabs(touchLocation.x - springBehavIoUr.anchorPoint.x);
CGFloat scrollResistance = (yDistanceFromTouch + xDistanceFromTouch) / 1500.0f;
UICollectionViewLayoutAttributes *item = (UICollectionViewLayoutAttributes*)[springBehavIoUr.items firstObject];
CGPoint center = item.center;
if (delta < 0) {
center.y += MAX(delta,delta*scrollResistance);
}
else {
center.y += MIN(delta,delta*scrollResistance);
}
item.center = center;
[weakDynamicAnimator updateItemUsingCurrentState:item];
}];
return NO;
}
@end
SampleCode的答案：
示例代码显示了这种奇怪的摆动效应,因为项目的大小是以编程方式生成的,并且不是四舍五入的 – 计算的精度会为UIDynamics和物理引擎创建问题,并且无法达到均衡.简单地舍入生成的项目大小给物理学一个机会.见NoteCollectionViewController.swift第77行.
func collectionView(collectionView: UICollectionView,layout collectionViewLayout: UICollectionViewLayout,sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
let w = round(CellAspectRatio.width * collectionView.frame.width)
let h = round(CellAspectRatio.height * collectionView.frame.height)
return CGSizeMake(w,h)
}
