当重复使用UICollectionView中的单元格时，重复使用的UICollectionViewCell的旧内容

Question

我正在使用UICollectionView来显示从URL异步加载的图片网格。我的收藏视图使用可重复使用的单元格来显示UICollectionViewCells。当单元格不被重用时，所有内容都可以正确显示，但当我滚动一下时，重用单元格会在旧内容开始正常行为之前短暂闪烁旧内容。

这里是习俗UICollectionViewController执行：

#import "MyCollectionViewViewController.h" 
#import "MyCollectionViewCell.h" 

@interface MyCollectionViewViewController()  
@property (strong, nonatomic) NSArray *data;  
@end 

@implementation MyCollectionViewViewController 

@synthesize data = _data; 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    self.data = @[ 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-851-1358529670-4.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr03/2013/1/18/11/enhanced-buzz-wide-26311-1358526816-5.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr03/2013/1/18/11/enhanced-buzz-wide-26311-1358527190-11.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr02/2013/1/18/11/enhanced-buzz-wide-7517-1358526694-11.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr03/2013/1/18/11/enhanced-buzz-wide-1965-1358527802-7.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr03/2013/1/18/11/enhanced-buzz-wide-2165-1358527708-14.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr03/2013/1/18/11/enhanced-buzz-wide-1965-1358527894-12.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr02/2013/1/18/12/enhanced-buzz-wide-15957-1358529198-18.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr02/2013/1/18/12/enhanced-buzz-wide-16520-1358528981-9.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr02/2013/1/18/12/enhanced-buzz-wide-16517-1358529292-5.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-20349-1358529323-20.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-32444-1358529959-9.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-32343-1358530043-7.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr02/2013/1/18/12/enhanced-buzz-wide-23646-1358530321-2.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-28223-1358530801-15.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-32273-1358530695-16.jpg", 
     @"http://s3-ec.buzzfed.com/static/enhanced/webdr01/2013/1/18/12/enhanced-buzz-wide-31288-1358531103-16.jpg" 
    ]; 

    [self.collectionView registerNib:[UINib nibWithNibName:@"MyCollectionViewCell" bundle:[NSBundle mainBundle]] forCellWithReuseIdentifier:@"myView"]; 
} 

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { 
    NSString *urlString = [self.data objectAtIndex:indexPath.item]; 

    MyCollectionViewCell *myView = [collectionView dequeueReusableCellWithReuseIdentifier:@"myView" forIndexPath:indexPath]; 
    myView.urlString = urlString; 

    [myView setNeedsDisplay]; 

    return myView; 
} 

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath { 
    return CGSizeMake(150, 150); 
} 

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView { 
    return 1; 
} 

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section { 
    return self.data.count; 
} 

@end 

这里是习俗UICollectionViewCell的实施。

#import "MyCollectionViewCell.h" 
#import <QuartzCore/QuartzCore.h> 
#import <AVFoundation/AVFoundation.h> 

@interface MyCollectionViewCell() 

@property (weak, nonatomic) IBOutlet UIImageView *imageView; 

@end 

@implementation MyCollectionViewCell 

@synthesize urlString = _urlString; 

+ (void)loadAsyncImageFromURL:(NSString *)urlString withCallback:(void (^)(UIImage *))callback { 
    NSURL *url = [NSURL URLWithString:urlString]; 

    dispatch_queue_t downloadQueue = dispatch_queue_create("com.example.downloadqueue", NULL); 
    dispatch_async(downloadQueue, ^{ 
     NSData * imageData = [NSData dataWithContentsOfURL:url]; 
     UIImage *image = [UIImage imageWithData:imageData]; 

     dispatch_async(dispatch_get_main_queue(), ^{ 
      callback(image); 
     }); 
    }); 
} 

-(void) fadeInView:(UIView *)view WithSecondDuration:(double)duration { 
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"]; 
    animation.beginTime = 0; 
    animation.duration = duration; 
    animation.fromValue = [NSNumber numberWithFloat:0.0f]; 
    animation.toValue = [NSNumber numberWithFloat:1.0f]; 
    animation.removedOnCompletion = NO; 
    animation.fillMode = kCAFillModeBoth; 
    animation.additive = NO; 
    [view.layer addAnimation:animation forKey:@"opacityIN"]; 
} 

- (void) setUrlString:(NSString *)urlString { 
    _urlString = urlString; 

    self.imageView.image = nil; 
    self.imageView.layer.opacity = 0; 

    if (urlString) { 
     [MyCollectionViewCell loadAsyncImageFromURL:urlString withCallback:^(UIImage *image) { 
      self.imageView.image = image; 
      [self fadeInView:self.imageView WithSecondDuration:.25]; 
     }]; 
    } 
} 


@end 

Answer 1

当单元格完成显示时，您可以尝试将单元格的URL设置为零，它对我的​​项目起作用。

-(void)collectionView:(UICollectionView *)cv didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath 
{ 
    [(MyCollectionViewCell *)cell setUrlString:nil]; 
} 

我希望这有助于！

Answer 2

您可以在您的UICollectionViewCell子类中实现-(void)prepareForReuse。并在那里做你的重置。

Answer 3

This文章显示@Weston和@architectpianist解决方案之间的区别。

总之：由于iOS10 -(void)prepareForReuse是更优化的。