我已经阅读了很多关于滚动不佳的 UICollectionView 帖子，但似乎没有一个直接适用或仍未得到答复。

我正在使用 AFNetworking 将图像(95 平方像素)异步加载到每个单元格上，然后当图像再次滚动到 View 中时，图像将从缓存中恢复(由响应验证)代码为 0 而不是 200)。

这是我尝试过的:

• 注释掉 weakCell.photoView.image = image; 这样图像就不会绘制在屏幕上并且滚动更顺畅(在 HTTP 获取期间仍然有点卡顿)
• 从 cellForRowAtIndexPath 方法中删除了所有 AFNetworking 代码，滚动更加流畅(即使自定义单元格阴影等仍在屏幕上绘制)
• 当我在屏幕上仅绘制单元格 View (带阴影)时，滚动 100 个单元格非常流畅。一旦我开始在屏幕上绘制图像，我的设备上的滚动效果就很差，甚至在模拟器上也很明显。 Instagram 在他们的个人资料 View 上有数百个单元格的滚动非常流畅，所以我试图接近他们的表现。

有什么方法可以改进下面的代码以提高滚动性能？

这是我的手机代码:

#import "PhotoGalleryCell.h"

@implementation PhotoGalleryCell

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {
        // Setup the background color, shadow, and border
        self.backgroundColor = [UIColor colorWithWhite:0.25f alpha:1.0f];
        self.layer.borderColor = [UIColor blackColor].CGColor;
        self.layer.borderWidth = 0.5f;
        self.layer.shadowColor = [UIColor blackColor].CGColor;
        self.layer.shadowRadius = 3.0f;
        self.layer.shadowOffset = CGSizeMake(0.0f, 2.0f);
        self.layer.shadowOpacity = 0.5f;

        // Make sure we rasterize for retina
        self.layer.rasterizationScale = [UIScreen mainScreen].scale;
        self.layer.shouldRasterize = YES;

        // Add to the content view
        self.photoView = [[UIImageView alloc] initWithFrame:self.bounds];
        [self.contentView addSubview:self.photoView];
    }

    return self;
}

- (void)prepareForReuse
{
    [super prepareForReuse];

    self.photoView.image = nil;
    self.largeImageURL = nil;
}

这是我的 UICollectionView 代码:

#pragma mark - Collection View Delegates

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

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return [zePhotos count];
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    PhotoGalleryCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:kPGPhotoCellIdentifier forIndexPath:indexPath];

    // Get a reference to the image dictionary
    NSDictionary *photoDict = [[zePhotos objectAtIndex:indexPath.row] objectForKey:@"image"];

    // Asynchronously set the thumbnail view
    __weak PhotoGalleryCell *weakCell = cell;
    NSString *thumbnailURL = [[photoDict objectForKey:@"thumbnail"] objectForKey:@"url"];
    NSURLRequest *photoRequest = [NSURLRequest requestWithURL:[NSURL URLWithString:thumbnailURL]];
    [cell.photoView setImageWithURLRequest:photoRequest
                          placeholderImage:nil
                                   success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                                       weakCell.photoView.image = image;
                                   }
                                   failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
                                       NSLog(@"Error retrieving thumbnail... %@", [error localizedDescription]);
                                   }];

    // Cache the large image URL in case they tap on this cell later
    cell.largeImageURL = [[photoDict objectForKey:@"large"] objectForKey:@"url"];

    return cell;
}

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
{
    [self performSegueWithIdentifier:@"showPhotoDetail" sender:self];
}

最佳答案

您可以尝试向您的 cell init 添加一个 shadowPath，它应该会提高性能，这是我在我的一个项目中使用的代码来添加一个圆形的 shadowPath(请参阅 UIBezierPath 方法以获得更多选择)

self.layer.shadowPath = [UIBezierPath bezierPathWithRoundedRect:self.frame.bounds
                                              byRoundingCorners:UIRectCornerAllCorners
                                                    cornerRadii:CGSizeMake(10, 10)].CGPath;

此外，如果我没记错的话，AFNetworking 不会调整从服务器返回的图像的大小，因此它可能会影响图像的质量(尽管您向 UIImageView 添加了缩放方法)，我建议分派(dispatch)返回的图像如果您愿意，可以调整它的大小:

CGSize targetSize = cell.photoView.bounds.size;
[cell.photoView setImageWithURLRequest:photoRequest
                      placeholderImage:nil
                               success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
                                    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
                                       CGFloat imageHeight = image.size.height;
                                       CGFloat imageWidth = image.size.width;

                                       CGSize newSize = weakCell.imageView.bounds.size;
                                       CGFloat scaleFactor = targetSize.width / imageWidth;
                                       newSize.height = imageHeight * scaleFactor;

                                       UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
                                       [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
                                       UIImage *small = UIGraphicsGetImageFromCurrentImageContext();
                                       UIGraphicsEndImageContext();

                                       dispatch_async(dispatch_get_main_queue(),^{
                                           weakCell.photoView.image = small;
                                       });
                                   });
                               }
                               failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
                                   NSLog(@"Error retrieving thumbnail... %@", [error localizedDescription]);
                               }];

关于ios - 使用 AFNetworking 加载图像的 UICollectionView 滚动性能，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18575625/