UICollectionView 重新加载数据无法更新 CollectionView
UICollectionView Reload Data Not Working to update CollectionView
更新：
我确实忘记提到 CollectionView 在 Split View Controller 的右侧，而在左侧，我有 tableView。选择一行后，我传递一个新的 FEED ADDRESS 并将其 运行 refreshFeed 方法放在右侧。
我有一个集合视图，它解析来自 XML 的数据。当按下某个按钮时，我希望它清除 CollectionView，并从不同的 XML 加载数据，这两个都位于在线。我使用 ASIHTTPRequest 和 GDATAXML 类 来帮助我实现这一目标。这是我的代码。我可以通过日志验证 NSMutableArray 是否已清除，并成功填充了不同的 XML，但 reloadData 永远不会发生，因为 cellForItem 不会被第二次调用。我哪里搞砸了？
@interface RightViewController ()
@property (nonatomic, strong) IBOutlet UICollectionView *collectionView;
@end
@implementation RightViewController
@synthesize allEntries = _allEntries;
@synthesize feeds = _feeds;
@synthesize queue = _queue;
@synthesize webViewController = _webViewController;
@synthesize activity;
@synthesize webViewController2 = _webViewController2;
@synthesize nameit2;
@synthesize nowplaying;
@synthesize entryofmp3 = _entryofmp3;
@synthesize nameit;
@synthesize progress;
@synthesize lastSelection;
@synthesize backgroundTaskIdentifier, theurl;
@synthesize thetable, thepath, downloadlabel, receivedData, progressbutton;
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return [_allEntries count];
}
- (void)loadFirstTime {
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
if (_feedAddress == nil) {
_feedAddress = @"http://www.316apps.com/AIMAPPLETV/AIMSeries.xml";
}
self.feeds = [NSArray arrayWithObjects:_feedAddress,
nil];
for (NSString *feed in _feeds) {
NSLog(@"Running Fine");
NSURL *url = [NSURL URLWithString:feed];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[_queue addOperation:request];
}
NSLog(@"Still Good");
//[self.collectionView reloadData];
}
-(void)changeFeed {
[_allEntries removeAllObjects];
_feedAddress = @"http://www.316apps.com/AIMAPPLETV/AIMCON.xml";
[self loadFirstTime];
// self.queue = nil;
//_request.delegate = nil;
// _request.delegate = nil;
// [_collectionView reloadData];
}
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
// [self performSegueWithIdentifier:@"playMovies" sender:self];
RSSEntry *entry = [_allEntries objectAtIndex:indexPath.row];
NSString *wifiStreamAddress = entry.articleUrl;
AVPlayer *player = [[AVPlayer alloc] initWithURL: [NSURL URLWithString: wifiStreamAddress] ];
AVPlayerViewController *playerViewController = [[AVPlayerViewController alloc] init];
playerViewController.player = player;
// Keep pointers to player and controller
self.player = player;
self.playerViewController = playerViewController;
[self presentViewController: playerViewController animated: true completion: ^{
[self.player play];
}];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
// Make sure your segue name in storyboard is the same as this line
if ([[segue identifier] isEqualToString:@"playMovies"])
{
PlayMovies *userViewController = [segue destinationViewController];
//if you need to pass data to the next controller do it here
}
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
RSSEntry *entry = [_allEntries objectAtIndex:indexPath.row];
static NSString *cellIdentifier = @"cvCell";
CVCell *cell = (CVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
[cell.theimage setImageWithURL:[NSURL URLWithString:entry.articleImage] placeholderImage:[UIImage imageNamed:@"icon@2x.png"]];
cell.theimage.adjustsImageWhenAncestorFocused = YES;
cell.theimage.clipsToBounds = false;
return cell;
}
- (void)viewDidLoad {
[super viewDidLoad];
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
[self loadFirstTime];
}
-(void) viewWillAppear:(BOOL)animated {
}
- (void)parseRss:(GDataXMLElement *)rootElement entries:(NSMutableArray *)entries {
NSArray *channels = [rootElement elementsForName:@"channel"];
for (GDataXMLElement *channel in channels) {
NSString *blogTitle = [channel valueForChild:@"title"];
NSArray *items = [channel elementsForName:@"item"];
for (GDataXMLElement *item in items) {
NSString *articleTitle = [item valueForChild:@"title"];
NSString *articleUrl = [[[[item elementsForName: @"enclosure"] lastObject] attributeForName: @"url"] stringValue];
NSString *articleDateString = [item valueForChild:@"pubDate"];
NSString *picture = [[[[item elementsForName: @"itunes:image"] lastObject] attributeForName: @"href"] stringValue];
NSDate *articleDate = [NSDate dateFromInternetDateTimeString:articleDateString formatHint:DateFormatHintRFC822];
RSSEntry *entry = [[RSSEntry alloc] initWithBlogTitle:blogTitle
articleTitle:articleTitle
articleUrl:articleUrl
articleDate:articleDate
articleImage:picture];
[entries addObject:entry];
NSLog(@"%@", entries);
}
}
[self.collectionView reloadData];
}
- (void)parseFeed:(GDataXMLElement *)rootElement entries:(NSMutableArray *)entries {
if ([rootElement.name compare:@"rss"] == NSOrderedSame) {
[self parseRss:rootElement entries:entries];
} else if ([rootElement.name compare:@"feed"] == NSOrderedSame) {
// [self parseAtom:rootElement entries:entries];
} else {
NSLog(@"Unsupported root element: %@", rootElement.name);
}
}
- (void)requestFinished:(ASIHTTPRequest *)request {
NSLog(@"Request Finished");
[_queue addOperationWithBlock:^{
NSError *error;
GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:[request responseData]
options:0 error:&error];
if (doc == nil) {
NSLog(@"Failed to parse %@", request.url);
} else {
NSMutableArray *entries = [NSMutableArray array];
[self parseFeed:doc.rootElement entries:entries];
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
for (RSSEntry *entry in entries) {
int insertIdx = [_allEntries indexForInsertingObject:entry sortedUsingBlock:^(id a, id b) {
RSSEntry *entry1 = (RSSEntry *) a;
RSSEntry *entry2 = (RSSEntry *) b;
return [entry1.articleDate compare:entry2.articleDate];
}];
[_allEntries insertObject:entry atIndex:insertIdx];
}
}];
}
}];
}
- (void)requestFailed:(ASIHTTPRequest *)request {
NSError *error = [request error];
NSLog(@"Error: %@", error);
[self loadFirstTime];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
第二次更新：
我正在慢慢到达某个地方。认为这是因为我没有设置 Segue。我从左侧 TableView 的 Cell 到 Collection View 的 View Controller 设置一个 segue 并设置为 ShowDetail，并命名它。然后在 LeftViewController 中：
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.row == 1) {
[self performSegueWithIdentifier:@"doingIt" sender:self];
}
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
// Make sure your segue name in storyboard is the same as this line
if ([[segue identifier] isEqualToString:@"doingIt"])
{
self.rightViewController = [[RightViewController alloc] init];
[self.rightViewController refresheyc];
//if you need to pass data to the next controller do it here
}
}
在 RightViewController 中我有：
-(void)refresheyc {
NSLog(@"This Sucks");
[self.allEntries removeAllObjects];
[self.collectionView reloadData];
self.allEntries = nil;
self.queue = nil;
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
self.feeds = [NSArray arrayWithObjects:@"http://www.316apps.com/AIMAPPLETV/AIMCON.xml",
nil];
for (NSString *feed in _feeds) {
NSURL *url = [NSURL URLWithString:feed];
NSLog(@"URL%@", url);
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[_queue addOperation:request];
}
}
CollectionView 中的 Cells 立即消失，但几秒钟后，它们都以相同的方式返回，根本没有改变 XML，但我明白了：
2016-01-09 14:37:31.542 AIM-TV[7965:522091] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
Stack:(
0 CoreFoundation 0x0000000109fa6ff5 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010d45cdeb objc_exception_throw + 48
2 CoreFoundation 0x0000000109fa6f2d +[NSException raise:format:] + 205
3 Foundation 0x000000010aa96341 _AssertAutolayoutOnMainThreadOnly + 79
4 Foundation 0x000000010a8f6d6e -[NSISEngine withBehaviors:performModifications:] + 31
5 UIKit 0x000000010c804eb8 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 58
6 UIKit 0x000000010c804854 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 646
7 UIKit 0x000000010c804ec1 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 67
8 UIKit 0x000000010c804589 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 242
9 UIKit 0x000000010c80405d -[UIView(AdditionalLayoutSupport) _initializeHostedLayoutEngine] + 649
10 UIKit 0x000000010c7f652a -[UIView(UIConstraintBasedLayout) _initializeLayoutEngine] + 152
11 UIKit 0x000000010c7f652a -[UIView(UIConstraintBasedLayout) _initializeLayoutEngine] + 152
12 UIKit 0x000000010c804e24 -[UIView(AdditionalLayoutSupport) _layoutEngineCreateIfNecessary] + 62
13 UIKit 0x000000010c7f732b -[UIView(UIConstraintBasedLayout) _tryToAddConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 126
14 UIKit 0x000000010c7f75ef -[UIView(UIConstraintBasedLayout) _addConstraint:] + 274
15 UIKit 0x000000010c7fd247 -[UIView(UIConstraintBasedLayout) _updateContentSizeConstraints] + 779
16 UIKit 0x000000010c806270 -[UIView(AdditionalLayoutSupport) updateConstraints] + 224
17 UIKit 0x000000010c80559b -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 550
18 UIKit 0x000000010c805866 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 198
19 UIKit 0x000000010c8054aa -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 309
20 UIKit 0x000000010c805866 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 198
21 UIKit 0x000000010c8054aa -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 309
22 UIKit 0x000000010c804ec1 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 67
23 UIKit 0x000000010c80583a -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 154
24 UIKit 0x000000010c805e9e __60-[UIView(AdditionalLayoutSupport) updateConstraintsIfNeeded]_block_invoke + 98
25 UIKit
您无法在后台线程中更新 UI 元素。 [self.collectionView reloadData] 是从 parseRss 调用的，parseRss 本身称为 parseFeed，由 _queue 上的操作调用。如果 _queue 恰好没有被主线程处理，您将在 collectionView 中得到不可预测的结果，并且更有可能崩溃。
您应该将对 [self.collectionView reloadData] 的调用分派到主线程。
dispatch_async(dispatch_get_main_queue(), { self.collectionView.reloadData() })
（这是Swift语法，我不熟悉Obj-C，抱歉）
问题真的很奇怪，但它对我有用，我在动画块中添加了更新约束代码，
UIView.animate(withDuration: 0.5, animations: {() -> Void in
//update constraints here
self.view.layoutIfNeeded()
self.collectionView.layoutIfNeeded()
})
self.collectionView.reloadData()
如阿兰的回答中所述，这是因为UI更改需要由主线程处理。我看到这个问题是 post 使用 Objective C 编辑的，并在 Swift 中回答，所以我想 post Objective C 版本以备不时之需。
dispatch_async(dispatch_get_main_queue(), ^ {
[self.collectionView reloadData];
});
除了@Alain T. 提到的将调用重新加载到 reloadData() 之外，请确保您的项目高度设置正确。当 itemHeight 为零或某个非常大的值时，您可能会看到
collectionView(numberOfItemsInSection) and numberOfSections()
按预期调用但不是你的
collectionView( cellForItemAt)。
因此请确保您已通过调用设置了项目高度：
collectionView(collectionView, layout, sizeForItemAt)
更新：
我确实忘记提到 CollectionView 在 Split View Controller 的右侧，而在左侧，我有 tableView。选择一行后，我传递一个新的 FEED ADDRESS 并将其 运行 refreshFeed 方法放在右侧。
我有一个集合视图，它解析来自 XML 的数据。当按下某个按钮时，我希望它清除 CollectionView，并从不同的 XML 加载数据，这两个都位于在线。我使用 ASIHTTPRequest 和 GDATAXML 类 来帮助我实现这一目标。这是我的代码。我可以通过日志验证 NSMutableArray 是否已清除，并成功填充了不同的 XML，但 reloadData 永远不会发生，因为 cellForItem 不会被第二次调用。我哪里搞砸了？
@interface RightViewController ()
@property (nonatomic, strong) IBOutlet UICollectionView *collectionView;
@end
@implementation RightViewController
@synthesize allEntries = _allEntries;
@synthesize feeds = _feeds;
@synthesize queue = _queue;
@synthesize webViewController = _webViewController;
@synthesize activity;
@synthesize webViewController2 = _webViewController2;
@synthesize nameit2;
@synthesize nowplaying;
@synthesize entryofmp3 = _entryofmp3;
@synthesize nameit;
@synthesize progress;
@synthesize lastSelection;
@synthesize backgroundTaskIdentifier, theurl;
@synthesize thetable, thepath, downloadlabel, receivedData, progressbutton;
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return [_allEntries count];
}
- (void)loadFirstTime {
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
if (_feedAddress == nil) {
_feedAddress = @"http://www.316apps.com/AIMAPPLETV/AIMSeries.xml";
}
self.feeds = [NSArray arrayWithObjects:_feedAddress,
nil];
for (NSString *feed in _feeds) {
NSLog(@"Running Fine");
NSURL *url = [NSURL URLWithString:feed];
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[_queue addOperation:request];
}
NSLog(@"Still Good");
//[self.collectionView reloadData];
}
-(void)changeFeed {
[_allEntries removeAllObjects];
_feedAddress = @"http://www.316apps.com/AIMAPPLETV/AIMCON.xml";
[self loadFirstTime];
// self.queue = nil;
//_request.delegate = nil;
// _request.delegate = nil;
// [_collectionView reloadData];
}
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
// [self performSegueWithIdentifier:@"playMovies" sender:self];
RSSEntry *entry = [_allEntries objectAtIndex:indexPath.row];
NSString *wifiStreamAddress = entry.articleUrl;
AVPlayer *player = [[AVPlayer alloc] initWithURL: [NSURL URLWithString: wifiStreamAddress] ];
AVPlayerViewController *playerViewController = [[AVPlayerViewController alloc] init];
playerViewController.player = player;
// Keep pointers to player and controller
self.player = player;
self.playerViewController = playerViewController;
[self presentViewController: playerViewController animated: true completion: ^{
[self.player play];
}];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
// Make sure your segue name in storyboard is the same as this line
if ([[segue identifier] isEqualToString:@"playMovies"])
{
PlayMovies *userViewController = [segue destinationViewController];
//if you need to pass data to the next controller do it here
}
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
RSSEntry *entry = [_allEntries objectAtIndex:indexPath.row];
static NSString *cellIdentifier = @"cvCell";
CVCell *cell = (CVCell *)[collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
[cell.theimage setImageWithURL:[NSURL URLWithString:entry.articleImage] placeholderImage:[UIImage imageNamed:@"icon@2x.png"]];
cell.theimage.adjustsImageWhenAncestorFocused = YES;
cell.theimage.clipsToBounds = false;
return cell;
}
- (void)viewDidLoad {
[super viewDidLoad];
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
[self loadFirstTime];
}
-(void) viewWillAppear:(BOOL)animated {
}
- (void)parseRss:(GDataXMLElement *)rootElement entries:(NSMutableArray *)entries {
NSArray *channels = [rootElement elementsForName:@"channel"];
for (GDataXMLElement *channel in channels) {
NSString *blogTitle = [channel valueForChild:@"title"];
NSArray *items = [channel elementsForName:@"item"];
for (GDataXMLElement *item in items) {
NSString *articleTitle = [item valueForChild:@"title"];
NSString *articleUrl = [[[[item elementsForName: @"enclosure"] lastObject] attributeForName: @"url"] stringValue];
NSString *articleDateString = [item valueForChild:@"pubDate"];
NSString *picture = [[[[item elementsForName: @"itunes:image"] lastObject] attributeForName: @"href"] stringValue];
NSDate *articleDate = [NSDate dateFromInternetDateTimeString:articleDateString formatHint:DateFormatHintRFC822];
RSSEntry *entry = [[RSSEntry alloc] initWithBlogTitle:blogTitle
articleTitle:articleTitle
articleUrl:articleUrl
articleDate:articleDate
articleImage:picture];
[entries addObject:entry];
NSLog(@"%@", entries);
}
}
[self.collectionView reloadData];
}
- (void)parseFeed:(GDataXMLElement *)rootElement entries:(NSMutableArray *)entries {
if ([rootElement.name compare:@"rss"] == NSOrderedSame) {
[self parseRss:rootElement entries:entries];
} else if ([rootElement.name compare:@"feed"] == NSOrderedSame) {
// [self parseAtom:rootElement entries:entries];
} else {
NSLog(@"Unsupported root element: %@", rootElement.name);
}
}
- (void)requestFinished:(ASIHTTPRequest *)request {
NSLog(@"Request Finished");
[_queue addOperationWithBlock:^{
NSError *error;
GDataXMLDocument *doc = [[GDataXMLDocument alloc] initWithData:[request responseData]
options:0 error:&error];
if (doc == nil) {
NSLog(@"Failed to parse %@", request.url);
} else {
NSMutableArray *entries = [NSMutableArray array];
[self parseFeed:doc.rootElement entries:entries];
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
for (RSSEntry *entry in entries) {
int insertIdx = [_allEntries indexForInsertingObject:entry sortedUsingBlock:^(id a, id b) {
RSSEntry *entry1 = (RSSEntry *) a;
RSSEntry *entry2 = (RSSEntry *) b;
return [entry1.articleDate compare:entry2.articleDate];
}];
[_allEntries insertObject:entry atIndex:insertIdx];
}
}];
}
}];
}
- (void)requestFailed:(ASIHTTPRequest *)request {
NSError *error = [request error];
NSLog(@"Error: %@", error);
[self loadFirstTime];
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
第二次更新：
我正在慢慢到达某个地方。认为这是因为我没有设置 Segue。我从左侧 TableView 的 Cell 到 Collection View 的 View Controller 设置一个 segue 并设置为 ShowDetail，并命名它。然后在 LeftViewController 中：
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.row == 1) {
[self performSegueWithIdentifier:@"doingIt" sender:self];
}
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
// Make sure your segue name in storyboard is the same as this line
if ([[segue identifier] isEqualToString:@"doingIt"])
{
self.rightViewController = [[RightViewController alloc] init];
[self.rightViewController refresheyc];
//if you need to pass data to the next controller do it here
}
}
在 RightViewController 中我有：
-(void)refresheyc {
NSLog(@"This Sucks");
[self.allEntries removeAllObjects];
[self.collectionView reloadData];
self.allEntries = nil;
self.queue = nil;
self.allEntries = [NSMutableArray array];
self.queue = [[NSOperationQueue alloc] init];
self.feeds = [NSArray arrayWithObjects:@"http://www.316apps.com/AIMAPPLETV/AIMCON.xml",
nil];
for (NSString *feed in _feeds) {
NSURL *url = [NSURL URLWithString:feed];
NSLog(@"URL%@", url);
ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];
[request setDelegate:self];
[_queue addOperation:request];
}
}
CollectionView 中的 Cells 立即消失，但几秒钟后，它们都以相同的方式返回，根本没有改变 XML，但我明白了：
2016-01-09 14:37:31.542 AIM-TV[7965:522091] This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes. This will cause an exception in a future release.
Stack:(
0 CoreFoundation 0x0000000109fa6ff5 __exceptionPreprocess + 165
1 libobjc.A.dylib 0x000000010d45cdeb objc_exception_throw + 48
2 CoreFoundation 0x0000000109fa6f2d +[NSException raise:format:] + 205
3 Foundation 0x000000010aa96341 _AssertAutolayoutOnMainThreadOnly + 79
4 Foundation 0x000000010a8f6d6e -[NSISEngine withBehaviors:performModifications:] + 31
5 UIKit 0x000000010c804eb8 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 58
6 UIKit 0x000000010c804854 __57-[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:]_block_invoke + 646
7 UIKit 0x000000010c804ec1 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 67
8 UIKit 0x000000010c804589 -[UIView(AdditionalLayoutSupport) _switchToLayoutEngine:] + 242
9 UIKit 0x000000010c80405d -[UIView(AdditionalLayoutSupport) _initializeHostedLayoutEngine] + 649
10 UIKit 0x000000010c7f652a -[UIView(UIConstraintBasedLayout) _initializeLayoutEngine] + 152
11 UIKit 0x000000010c7f652a -[UIView(UIConstraintBasedLayout) _initializeLayoutEngine] + 152
12 UIKit 0x000000010c804e24 -[UIView(AdditionalLayoutSupport) _layoutEngineCreateIfNecessary] + 62
13 UIKit 0x000000010c7f732b -[UIView(UIConstraintBasedLayout) _tryToAddConstraint:roundingAdjustment:mutuallyExclusiveConstraints:] + 126
14 UIKit 0x000000010c7f75ef -[UIView(UIConstraintBasedLayout) _addConstraint:] + 274
15 UIKit 0x000000010c7fd247 -[UIView(UIConstraintBasedLayout) _updateContentSizeConstraints] + 779
16 UIKit 0x000000010c806270 -[UIView(AdditionalLayoutSupport) updateConstraints] + 224
17 UIKit 0x000000010c80559b -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 550
18 UIKit 0x000000010c805866 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 198
19 UIKit 0x000000010c8054aa -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 309
20 UIKit 0x000000010c805866 -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 198
21 UIKit 0x000000010c8054aa -[UIView(AdditionalLayoutSupport) _internalUpdateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 309
22 UIKit 0x000000010c804ec1 -[UIView(AdditionalLayoutSupport) _withAutomaticEngineOptimizationDisabledIfEngineExists:] + 67
23 UIKit 0x000000010c80583a -[UIView(AdditionalLayoutSupport) _updateConstraintsIfNeededAccumulatingViewsNeedingSecondPassAndViewsNeedingBaselineUpdate:forSecondPass:] + 154
24 UIKit 0x000000010c805e9e __60-[UIView(AdditionalLayoutSupport) updateConstraintsIfNeeded]_block_invoke + 98
25 UIKit
您无法在后台线程中更新 UI 元素。 [self.collectionView reloadData] 是从 parseRss 调用的，parseRss 本身称为 parseFeed，由 _queue 上的操作调用。如果 _queue 恰好没有被主线程处理，您将在 collectionView 中得到不可预测的结果，并且更有可能崩溃。
您应该将对 [self.collectionView reloadData] 的调用分派到主线程。
dispatch_async(dispatch_get_main_queue(), { self.collectionView.reloadData() })
（这是Swift语法，我不熟悉Obj-C，抱歉）
问题真的很奇怪，但它对我有用，我在动画块中添加了更新约束代码，
UIView.animate(withDuration: 0.5, animations: {() -> Void in
//update constraints here
self.view.layoutIfNeeded()
self.collectionView.layoutIfNeeded()
})
self.collectionView.reloadData()
如阿兰的回答中所述，这是因为UI更改需要由主线程处理。我看到这个问题是 post 使用 Objective C 编辑的，并在 Swift 中回答，所以我想 post Objective C 版本以备不时之需。
dispatch_async(dispatch_get_main_queue(), ^ {
[self.collectionView reloadData];
});
除了@Alain T. 提到的将调用重新加载到 reloadData() 之外，请确保您的项目高度设置正确。当 itemHeight 为零或某个非常大的值时，您可能会看到
collectionView(numberOfItemsInSection) and numberOfSections()
按预期调用但不是你的
collectionView( cellForItemAt)。
因此请确保您已通过调用设置了项目高度：
collectionView(collectionView, layout, sizeForItemAt)