Ios UICollection视图单元格重绘错误
我对重新绘制uicollectionview单元格的图像有意见-图像是从URL下载的,从JSON解析而来。我有10个单元格,在应用程序启动时,只显示前6个单元格,但没有加载图像,当我向下滚动到其他单元格时,它们有图像,当我向后滚动到顶部时,前4个单元格也有图像,只有单元格5和6没有被重绘(它们在整个时间内都可见)。我一直在尝试调试这个很长时间,但没有成功 在cellForItemAtIndexPath中,我调用SDWebImage(但这并不重要): 但当第一次调用cellForItemAtIndexPath时,timeSnap.thumbnailImageURL(其中timeSnap实体是单元格的模型)尚未初始化,因此为空 初始化timeSnap.thumbnailImageURL后,我有:Ios UICollection视图单元格重绘错误,ios,objective-c,image,uicollectionview,Ios,Objective C,Image,Uicollectionview,我对重新绘制uicollectionview单元格的图像有意见-图像是从URL下载的,从JSON解析而来。我有10个单元格,在应用程序启动时,只显示前6个单元格,但没有加载图像,当我向下滚动到其他单元格时,它们有图像,当我向后滚动到顶部时,前4个单元格也有图像,只有单元格5和6没有被重绘(它们在整个时间内都可见)。我一直在尝试调试这个很长时间,但没有成功 在cellForItemAtIndexPath中,我调用SDWebImage(但这并不重要): 但当第一次调用cellForItemAtInd
dispatch_async(dispatch_get_main_queue(), ^{
[self.collectionView reloadData];
});
edit1:
添加我的代码有点复杂-首先,我将从服务器API获取JSON,其中包含要在集合视图中显示的项,然后对于每个项,我必须从服务器API获取另一个JSON,从中我可以构建timeSnap.thumbnailImageURL的URL
视图控制器类:
- (void)viewDidLoad
{
[super viewDidLoad];
[self refreshNewTimeSnapsFeed];
}
- (void)refreshNewTimeSnapsFeed {
Adapter *adapter = [AppDelegate instance].adapter;
[adapter getNewTimeSnapsWithCompletion:^(NSArray* jsonResponse) {
[self newTimeSnapsFeedRefreshed:jsonResponse];
}];
}
- (void)newTimeSnapsFeedRefreshed:(NSArray*)jsonResponse {
Adapter *adapter = [AppDelegate instance].adapter;
for (NSDictionary *timeSnapDict in jsonResponse) {
TimeSnap *timeSnap = [[TimeSnap alloc] initWithJSON:timeSnapDict];
[adapter getTimeSnapSnapsforId:timeSnap.id withCompletion:^(NSArray* jsonResponse) {
[timeSnap getSnapsJSON:jsonResponse];
[timeSnap getTimeSnapThumbnailImageURL];
}];
[self.timeSnaps addObject:timeSnap];
}
dispatch_async(dispatch_get_main_queue(), ^{
[self.collectionView reloadData];
});
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
TimeSnapCell *cell = (TimeSnapCell*)[collectionView dequeueReusableCellWithReuseIdentifier:@"TimeSnapCell" forIndexPath:indexPath];
TimeSnap *timeSnap = self.timeSnaps[indexPath.row];
cell.label.text = timeSnap.name;
[cell.backgroundImage setImageWithURL:[NSURL URLWithString:timeSnap.thumbnailImageURL] placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
return cell;
}
适配器类:
- (void)getNewTimeSnapsWithCompletion:(void (^)(NSArray* jsonResponse))completion {
NSString *urlAsString = [NSString stringWithFormat:@"..."];
NSURL *url = [[NSURL alloc] initWithString:urlAsString];
[self getJSONWithCompletion:completion fromURL:url forKey:@"Items"];
}
- (void)getTimeSnapSnapsforId:(NSNumber*)id withCompletion:(void (^)(NSArray* jsonResponse))completion {
NSString *urlAsString = [NSString stringWithFormat:@"..."];
NSURL *url = [[NSURL alloc] initWithString:urlAsString];
[self getJSONWithCompletion:completion fromURL:url forKey:@"Items"];
}
- (void)getJSONWithCompletion:(void (^)(NSArray* jsonResponse))completion fromURL:(NSURL*)url forKey:(NSString*)key {
//code for getting JSON from server API, then parsing into NSArray *items
dispatch_async(dispatch_get_main_queue(), ^{
if(completion){
completion(items);
}
});
}
删除reloadData中的分派,同时删除reloadData并仅添加以下代码
dispatch_async(dispatch_get_main_queue(), ^{
[cell.backgroundImage setImageWithURL:[NSURL URLWithString:timeSnap.thumbnailImageURL] placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
});
删除reloadData中的分派,同时删除reloadData并仅添加以下代码
dispatch_async(dispatch_get_main_queue(), ^{
[cell.backgroundImage setImageWithURL:[NSURL URLWithString:timeSnap.thumbnailImageURL] placeholderImage:[UIImage imageNamed:@"placeholder.png"]];
});
当第二个JSON响应返回时,需要重新加载单元格:
for (NSDictionary *timeSnapDict in jsonResponse) {
TimeSnap *timeSnap = [[TimeSnap alloc] initWithJSON:timeSnapDict];
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.timeSnaps.count inSection:0];
[self.timeSnaps addObject:timeSnap];
[adapter getTimeSnapSnapsforId:timeSnap.id withCompletion:^(NSArray* jsonResponse) {
[timeSnap getSnapsJSON:jsonResponse];
[timeSnap getTimeSnapThumbnailImageURL];
[self.collectionView reloadItemsAtIndexPaths:@[indexPath]];
}];
}
您的适配器类在主队列上执行完成块,因此您不需要使用<代码> DeXCHOYASYNC/<代码>(除非您不考虑适配器的合同的一部分).< /P> < P>当第二个JSON响应返回时,您需要重新加载单元格:
for (NSDictionary *timeSnapDict in jsonResponse) {
TimeSnap *timeSnap = [[TimeSnap alloc] initWithJSON:timeSnapDict];
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.timeSnaps.count inSection:0];
[self.timeSnaps addObject:timeSnap];
[adapter getTimeSnapSnapsforId:timeSnap.id withCompletion:^(NSArray* jsonResponse) {
[timeSnap getSnapsJSON:jsonResponse];
[timeSnap getTimeSnapThumbnailImageURL];
[self.collectionView reloadItemsAtIndexPaths:@[indexPath]];
}];
}
您的适配器类在主队列上执行完成块,因此您不需要使用<代码> DeXCHCHYASYNC <代码>(除非您不考虑适配器的合同的一部分)。请提供代码。请查看它。提供代码。请查看IITI,谢谢您的回复。我正在使用SDWebImage库进行图像下载和缓存,它负责发送本身,如果我将发送删除到reloadData和reloadData中,则不会显示任何内容,我将提供更清晰的代码嗨,感谢您的回复,我正在使用SDWebImage库进行图像下载和缓存,它负责调度本身,如果我将调度删除到reloadData和reloadData中,则不会显示任何内容,我将提供代码以使其更清晰