Ios UICollectionView仅在滚动时加载图像
我很难在数据解析后加载UICollectionView图像 这是苹果公司提供的一个懒散的解决方案,任何东西都可以在tableview上工作,但对于 CollectionView图像仅在我滚动时显示。其他数据,如标签或其他标签 手机没有问题,只有图像给我带来麻烦 我的委托中有一个重载方法:Ios UICollectionView仅在滚动时加载图像,ios,objective-c,uicollectionview,Ios,Objective C,Uicollectionview,我很难在数据解析后加载UICollectionView图像 这是苹果公司提供的一个懒散的解决方案,任何东西都可以在tableview上工作,但对于 CollectionView图像仅在我滚动时显示。其他数据,如标签或其他标签 手机没有问题,只有图像给我带来麻烦 我的委托中有一个重载方法: __block ParseOperation *weakParser = parser; parser.completionBlock = ^(void) { if (weak
__block ParseOperation *weakParser = parser;
parser.completionBlock = ^(void) {
if (weakParser.appRecordList) {
dispatch_async(dispatch_get_main_queue(), ^{
CategroyScreenViewController *rootViewController = (CategroyScreenViewController*)[(UINavigationController*)self.window.rootViewController topViewController];
rootViewController.entries = weakParser.appRecordList;
[rootViewController.collectionView reloadData];
});
}
self.queue = nil;
};
[self.queue addOperation:parser];
self.appListData = nil;
}
这是我的CategroyScreenView控制器,包含collectionview:
#define kCustomRowCount 7
@interface CategroyScreemViewController () <UIScrollViewDelegate>
@property (nonatomic, strong) NSMutableDictionary *imageDownloadsInProgress;
@property (nonatomic) NSMutableArray* numbers;
@end
int num = 0;
@implementation CategroyScreemViewController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
// Custom initialization
}
return self;
}
- (void)viewDidLoad
{
NSLog(@"view did load");
[super viewDidLoad];
self.imageDownloadsInProgress = [NSMutableDictionary dictionary];
[self.collectionView reloadData];
}
- (CGSize) blockSizeForItemAtIndexPath:(NSIndexPath *)indexPath {
NSLog(@"Asking for index paths of non-existant cells!! %d", indexPath.row);
if (indexPath.row == 0) return CGSizeMake(2, 2);
return CGSizeMake(1, 1);
}
- (void) viewDidAppear:(BOOL)animated {
NSLog(@"viewDidAppear load");
[self.collectionView reloadData];
}
- (UIEdgeInsets)insetsForItemAtIndexPath:(NSIndexPath *)indexPath {
NSLog(@"insetsForItemAtIndexPath load");
return UIEdgeInsetsMake(2, 2, 2, 2);
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
NSArray *allDownloads = [self.imageDownloadsInProgress allValues];
[allDownloads makeObjectsPerformSelector:@selector(cancelDownload)];
[self.imageDownloadsInProgress removeAllObjects];
}
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
NSLog(@"numberOfSectionsInCollectionView load");
return 1;
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
NSUInteger count = [self.entries count];
NSLog(@"numberOfItemsInSection load");
if (count == 0)
{
return kCustomRowCount;
}
return count;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CategoryScreenCell *myCell = [collectionView dequeueReusableCellWithReuseIdentifier:@"MyCell" forIndexPath:indexPath];
UILabel *label = (UILabel *)[myCell.contentView viewWithTag:10];
NSUInteger nodeCount = [self.entries count];
if (nodeCount > 0)
{
AppRecord *appRecord = [self.entries objectAtIndex:indexPath.row];
[label setText:appRecord.appName];
if (!appRecord.appIcon)
{
if (self.collectionView.dragging == NO && self.collectionView.decelerating == NO)
{
[self startIconDownload:appRecord forIndexPath:indexPath];
}
myCell.imageView.image = [UIImage imageNamed:@"Placeholder.png"];
}
else
{
myCell.imageView.image = appRecord.appIcon;
}
}
return myCell;
}
- (UIColor*) colorForNumber:(NSNumber*)num {
return [UIColor colorWithHue:((19 * num.intValue) % 255)/255.f saturation:1.f brightness:1.f alpha:1.f];
}
- (void)startIconDownload:(AppRecord *)appRecord forIndexPath:(NSIndexPath *)indexPath
{
IconDownloader *iconDownloader = [self.imageDownloadsInProgress objectForKey:indexPath];
if (iconDownloader == nil)
{
iconDownloader = [[IconDownloader alloc] init];
iconDownloader.appRecord = appRecord;
[iconDownloader setCompletionHandler:^{
CategoryScreenCell *myCell = [self.collectionView dequeueReusableCellWithReuseIdentifier:@"MyCell" forIndexPath:indexPath];
myCell.imageView.image = appRecord.appIcon;
myCell.imageView.layer.masksToBounds = YES;
[self.imageDownloadsInProgress removeObjectForKey:indexPath];
}];
[self.imageDownloadsInProgress setObject:iconDownloader forKey:indexPath];
[iconDownloader startDownload];
}
}
- (void)loadImagesForOnscreenRows
{
NSLog(@"loadImagesForOnscreenRows");
if ([self.entries count] > 0)
{
NSArray *visiblePaths = [self.collectionView indexPathsForVisibleItems];
for (NSIndexPath *indexPath in visiblePaths)
{
AppRecord *appRecord = [self.entries objectAtIndex:indexPath.item];
if (!appRecord.appIcon)
// Avoid the app icon download if the app already has an icon
{
[self startIconDownload:appRecord forIndexPath:indexPath];
}
}
}
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
NSLog(@"scrollViewDidEndDragging");
if (!decelerate)
{
NSLog(@"decelerate");
[self loadImagesForOnscreenRows];
}
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
NSLog(@"scrollViewDidEndDecelerating");
[self loadImagesForOnscreenRows];
}
@end
对于这一点:
CategoryScreenCell *myCell = [self.collectionView cellForItemAtIndexPath:indexPath];
程序运行良好,但它给了我以下警告:
不兼容的指针类型正在使用类型为的表达式初始化“CategoryScreenCell*”
“UICollectionViewCell*”您可以通过强制转换单元格类型来消除警告,前提是您知道它将是所需的类型:
CategoryScreenCell *myCell = (CategoryScreenCell *)[self.collectionView cellForItemAtIndexPath:indexPath];
我看到这种方法的问题是,在你的
IconDownloader
的完成处理程序中,你总是将一个单元格出列并填充它,即使它不可见也可能不显示。我不确定这会有多大的开销——这取决于你有多少单元格以及人们滚动的速度
一种替代方法是在完成处理程序中发布通知,所有单元格都将注册该通知。在通知发生时调用的方法中,单元格将检查通知的userInfo
中的AppRecord
是否用于当前单元格,并更新其映像
另一个问题是,您为滚动经过的每个单元格排队下载图像,因此如果用户快速滚动到集合视图的底部,他们必须等待上面的所有图像首先加载。您可以通过以下几种方法解决此问题:
1) 退出队列时,为单元格提供对IconDownloader
的引用。然后在单元格的prepareForReuse
中,如果仍挂起,请取消下载
2) 如果您不想取消挂起的下载,但想确保可见单元格尽快更新,可以将下载放入优先级队列,并增加每个新的IconDownloader
实例的优先级
CategoryScreenCell *myCell = (CategoryScreenCell *)[self.collectionView cellForItemAtIndexPath:indexPath];