当从UICollectionView插入或删除项目时，似乎在动画期间出现了一个额外的单元格，并且这个额外的单元格向错误的方向移动。我用UITableView尝试过完全一样，没有问题。
问题的视频在这里：https://dl.dropbox.com/u/11523469/CollectionViewBug.mov，左侧是集合视图，右侧是表格视图。每个单元格中的数字是创建单元格时单元格的indexPath.item值。
在0:08和0:12（插入）之间的视频中首先出现问题，然后再次在0:16到0:20（删除）。
项目可在此处：https://dl.dropbox.com/u/11523469/CollectionViewBug.zip
即。插入单元格时，插入单元格下方的所有单元格都向下移动，为新单元格腾出空间。但是这个额外的细胞出现并与其他细胞重叠并向上移动。
同样，当删除一个单元格时，被删除单元格下方的所有单元格都会向上移动以填充该单元格所在的间隙。但是这个额外的细胞出现并与其他细胞重叠并向下移动。
要对集合视图执行的第一个操作（插入或删除）不会导致此问题。但是在随后的所有行动中，问题都存在。
是否有其他人遇到过与UICollectionView相同的问题？有没有人有解决方案或解决方法？
谢谢！
答案 0 :(得分：10)
我提出了一个似乎可以解决问题的解决方法，但是对于提供的示例非常具体。我的猜测是，当细胞被重复使用时，它们会有错误的起点导致奇怪的动画。
我更改了故事板以使用UICollectionViewFlowLayout的子类：
// MyFlowLayout - subclass of UICollectionViewFlowLayout
#import "MyFlowLayout.h"
@interface MyFlowLayout ()
@property (strong) NSMutableArray *deleteIndexPaths;
@property (strong) NSMutableArray *insertIndexPaths;
@property (assign) float rowOffset;
@end
@implementation MyFlowLayout
-(id)initWithCoder:(NSCoder *)aDecoder
{
if (self = [super initWithCoder:aDecoder])
{
// minimumInteritemSpacing may be adjusted upwards but this example ignores that
self.rowOffset = self.itemSize.height + self.minimumInteritemSpacing;
}
return self;
}
// As per Mark Pospesel corrections to CircleLayout
- (void)prepareForCollectionViewUpdates:(NSArray *)updateItems
{
// Keep track of insert and delete index paths
[super prepareForCollectionViewUpdates:updateItems];
self.deleteIndexPaths = [NSMutableArray array];
self.insertIndexPaths = [NSMutableArray array];
for (UICollectionViewUpdateItem *update in updateItems)
{
if (update.updateAction == UICollectionUpdateActionDelete)
{
[self.deleteIndexPaths addObject:update.indexPathBeforeUpdate];
}
else if (update.updateAction == UICollectionUpdateActionInsert)
{
[self.insertIndexPaths addObject:update.indexPathAfterUpdate];
}
}
}
- (void)finalizeCollectionViewUpdates
{
[super finalizeCollectionViewUpdates];
// release the insert and delete index paths
self.deleteIndexPaths = nil;
self.insertIndexPaths = nil;
}
// The next two methods have misleading names as they get called for all visible cells on both insert and delete
- (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
// Must call super
UICollectionViewLayoutAttributes *attributes = [super initialLayoutAttributesForAppearingItemAtIndexPath:itemIndexPath];
if (!attributes)
attributes = [self layoutAttributesForItemAtIndexPath:itemIndexPath];
if ([self.insertIndexPaths containsObject:itemIndexPath]) {
// Initial position for an inserted cell is it's final position - fades in
CGRect frame = attributes.frame;
frame.origin.y = itemIndexPath.row * self.rowOffset;
attributes.frame = frame;
attributes.zIndex = -1; // stop the inserted cell bleeding through too early in the animation
}
if ([self.deleteIndexPaths count]) {
NSIndexPath *deletedPath = self.deleteIndexPaths[0]; // Might be more than one but this example ignores that
if (itemIndexPath.row > deletedPath.row) {
// Anything after the deleted cell needs to slide up from the position below it's final position
// Anything before the deleted cell doesn't need adjusting
CGRect frame = attributes.frame;
frame.origin.y = ((itemIndexPath.row + 1) * self.rowOffset);
attributes.frame = frame;
}
}
return attributes;
}
- (UICollectionViewLayoutAttributes *)finalLayoutAttributesForDisappearingItemAtIndexPath:(NSIndexPath *)itemIndexPath
{
UICollectionViewLayoutAttributes *attributes = [super finalLayoutAttributesForDisappearingItemAtIndexPath:itemIndexPath];
if (!attributes)
attributes = [self layoutAttributesForItemAtIndexPath:itemIndexPath];
// I would have expected the final positions to already be correct but my guess is that re-used cells
// are not considered until after the animation block settings have been generated
CGRect frame = attributes.frame;
frame.origin.y = itemIndexPath.row * self.rowOffset;
attributes.frame = frame;
if ([self.deleteIndexPaths containsObject:itemIndexPath]) {
// Fade out the deleted cell
attributes.alpha = 0.0;
}
return attributes;
}
@end
答案 1 :(得分：1)
如果有人来到这里寻找MonoTouch的答案，这就是我通过翻译Gareth's answer得到的。
定义EnableAnimationFix的基类和两个虚拟方法：ApplyAnimationFixToAppearingItem和ApplyAnimationFixToDisappearingItem。
public class CollectionViewFlowLayout : UICollectionViewFlowLayout
{
protected List<int> _insertedItems = new List<int> ();
protected List<int> _deletedItems = new List<int> ();
protected virtual bool EnableAnimationFix {
get { return false; }
}
protected virtual void ApplyAnimationFixToAppearingItem (int index, UICollectionViewLayoutAttributes attrs)
{
throw new NotImplementedException ();
}
protected virtual void ApplyAnimationFixToDisappearingItem (int index, UICollectionViewLayoutAttributes attrs)
{
throw new NotImplementedException ();
}
public override UICollectionViewLayoutAttributes InitialLayoutAttributesForAppearingItem (NSIndexPath path)
{
var attrs = base.InitialLayoutAttributesForAppearingItem (path);
if (!EnableAnimationFix) {
return attrs;
}
attrs = attrs ?? LayoutAttributesForItem (path);
if (attrs != null)
ApplyAnimationFixToAppearingItem (path.Row, attrs);
return attrs;
}
public override UICollectionViewLayoutAttributes FinalLayoutAttributesForDisappearingItem (NSIndexPath path)
{
var attrs = base.FinalLayoutAttributesForDisappearingItem (path);
if (!EnableAnimationFix) {
return attrs;
}
if (attrs == null && _deletedItems.Contains (path.Row)) {
// Calling LayoutAttributesForItem will cause an exception so we return now.
// I think this happens when last and only item is deleted, and there are no other cells in cell pool.
return null;
}
attrs = attrs ?? LayoutAttributesForItem (path);
if (attrs != null)
ApplyAnimationFixToDisappearingItem (path.Row, attrs);
return attrs;
}
public override void PrepareForCollectionViewUpdates (UICollectionViewUpdateItem [] updateItems)
{
base.PrepareForCollectionViewUpdates (updateItems);
if (!EnableAnimationFix)
return;
_insertedItems.Clear ();
_deletedItems.Clear ();
foreach (var update in updateItems) {
if (update.UpdateAction == UICollectionUpdateAction.Insert) {
_insertedItems.Add (update.IndexPathAfterUpdate.Row);
} else if (update.UpdateAction == UICollectionUpdateAction.Delete) {
_deletedItems.Add (update.IndexPathBeforeUpdate.Row);
}
}
}
public override void FinalizeCollectionViewUpdates ()
{
base.FinalizeCollectionViewUpdates ();
if (!EnableAnimationFix)
return;
_insertedItems.Clear ();
_deletedItems.Clear ();
}
}
我的实际集合视图布局代码：
public class DraftsLayout : CollectionViewFlowLayout
{
// ...
protected override bool EnableAnimationFix {
get { return true; }
}
protected override void ApplyAnimationFixToAppearingItem (int index, UICollectionViewLayoutAttributes attrs)
{
if (_insertedItems.Contains (index)) {
SetXByIndex (attrs, index);
attrs.ZIndex = -1;
}
int deletedToTheLeft = _deletedItems.Count (i => i < index);
if (deletedToTheLeft > 0) {
SetXByIndex (attrs, index + deletedToTheLeft);
}
}
protected override void ApplyAnimationFixToDisappearingItem (int index, UICollectionViewLayoutAttributes attrs)
{
SetXByIndex (attrs, index);
if (_deletedItems.Contains (index)) {
attrs.Alpha = 0;
}
}
const int SnapStep = 150;
static void SetXByIndex (UICollectionViewLayoutAttributes attrs, int index)
{
var frame = attrs.Frame;
frame.X = index * SnapStep;
attrs.Frame = frame;
}
}
请注意，此代码应该可以很好地处理批处理中的多个删除 感谢Gareth。
答案 2 :(得分：0)
我一直在使用reloadData或reloadItemsAtIndexPaths来处理各种奇怪的动画行为。当我不使用这些方法时，动画行为似乎与宣传的一样。