UICollectionView重新加載數據無法更新CollectionView

Question

UPDATTE：

我忘記提到CollectionView位於Split View Controller的右側，而在左側，我有tableView。 當選擇一行時，我傳遞一個新的FEED ADDRESS並讓它在右側運行refreshFeed方法。

我有一個集合視圖，用於解析XML中的數據。 當按下某個按鈕時，我希望它清除CollectionView，並從不同的XML加載數據，這兩個XML都在線。 我使用ASIHTTPRequest和GDATAXML類來幫助我解決這個問題。 這是我的代碼。 我可以通過日志驗證NSMutableArray已被清除，並成功填充了不同的XML，但reloadData永遠不會發生，因為第二次不會調用cellForItem。 我搞砸了哪里？

@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：

我慢慢地到了某個地方。 認為這是因為我沒有設置Segue。 我將左側CellView的一個segue吸收到Collection View的View Controller並設置為ShowDetail，並將其命名。 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，但幾秒鍾之后，它們都回來了，完全沒有改變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

Answer 1

您無法在后台線程中更新UI元素。 [self.collectionView reloadData]是從parseRss調用的，parseRss本身稱為表單parseFeed，由_queue上的操作調用。 如果_queue沒有碰巧被主線程處理，你將在collectionView中獲得不可預測的結果，並且更有可能崩潰。

您應該將對[self.collectionView reloadData]的調用發送到主線程。

dispatch_async(dispatch_get_main_queue(), { self.collectionView.reloadData() })

（這是Swift語法，我不熟悉Obj-C，抱歉）

Answer 2

問題真的很奇怪，但它在某種程度上對我有用，我在動畫塊中添加了更新約束代碼，

UIView.animate(withDuration: 0.5, animations: {() -> Void in

    //update constraints here

    self.view.layoutIfNeeded() 
    self.collectionView.layoutIfNeeded()

})

self.collectionView.reloadData()

Answer 3

正如Alain的回答所述 ，這是因為UI更改需要由主線程處理。 我看到問題是使用Objective C發布的，並在Swift中回答，所以我認為我會發布Objective C版本以防任何人需要它。

dispatch_async(dispatch_get_main_queue(), ^ {
    [self.collectionView reloadData];
});

Answer 4

除了@Alain T.提到wrt dspatching對reloadData（）的調用之外，請確保你的項目高度設置得恰當。 當itemHeight為零或某個非常大的值時，您可能會看到按預期調用的collectionView(numberOfItemsInSection) and numberOfSections() ，而不是您的collectionView( cellForItemAt) 。

因此，請確保通過調用設置項目高度：

collectionView(collectionView, layout, sizeForItemAt)