Ios UITableViewCells中的图像加载错误
我正在开发一个应用程序,我想在自定义单元格的UITableView中显示几乎和屏幕大小一样大的图像。 图像加载良好,虽然有点慢,但加载速度很快,但当我在TableView中滚动时,它们出现在错误的单元格中(例如,在Cell5中的Image1,Image5应该出现在该单元格中),1秒或2秒后,正确的图像会出现。 为了不产生太多的数据流量,我想到了一种类似“缓存”的URL/图像存储,如下所示:Ios UITableViewCells中的图像加载错误,ios,uitableview,uiimage,Ios,Uitableview,Uiimage,我正在开发一个应用程序,我想在自定义单元格的UITableView中显示几乎和屏幕大小一样大的图像。 图像加载良好,虽然有点慢,但加载速度很快,但当我在TableView中滚动时,它们出现在错误的单元格中(例如,在Cell5中的Image1,Image5应该出现在该单元格中),1秒或2秒后,正确的图像会出现。 为了不产生太多的数据流量,我想到了一种类似“缓存”的URL/图像存储,如下所示: - (id) init { if (self = [super init]) {
- (id) init
{
if (self = [super init]) {
self.cacheStoreDictionary = [NSMutableDictionary new];
}
return self;
}
- (void) startLoadingImageWithUrl:(NSString *)urlString forItem:(id)item
{
if (self.cacheStoreDictionary[urlString]) {
UIImage *image = self.cacheStoreDictionary[urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:YES];
} else {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
UIImage *image = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
[self.cacheStoreDictionary setObject:image forKey:urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:NO];
});
});
}
}
- (void)fetchTicketEvents
{
// Login URL
NSURL *eventsURL = [NSURL URLWithString:TH_API_BASEURL];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:eventsURL];
httpClient.parameterEncoding = AFJSONParameterEncoding;
// Set request parameters
NSDictionary *params = nil;
NSMutableURLRequest *request = [httpClient requestWithMethod:@"GET"
path:TH_API_PATH_TICKET_EVENT_INDEX
parameters:params];
request.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
// Prepare request
AFJSONRequestOperation *eventsRequest = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
if ([self.delegate respondsToSelector:@selector(thAPITicket:didLoadTicketEvents:response:errorCode:)]) {
NSArray *jsonEventArray = JSON;
NSMutableArray *event = [[NSMutableArray alloc] initWithCapacity:jsonEventArray.count];
for (NSDictionary *eventDictionary in [JSON allObjects]) {
[event addObject:[LCEvent eventFromDictionary:eventDictionary]];
}
[self.delegate thAPITicket:self
didLoadTicketEvents:YES
response:@{@"response" : response, @"json" : JSON, @"event" : event}
errorCode:TH_API_ERR_TICKETINDEX_NO_ERROR];
#if LOG_NETWORKING
[self printJSON:JSON];
#endif
//Network indicator off
[LCSharedInstance hideNetworkActivity];
//Allow Slide-To-Refresh
[LCSharedInstance singletone].allowSlideToRefresh = YES;
[LCSharedInstance singletone].isShownLoadingMessage = NO;
[LCSharedInstance singletone].isLoading = NO;
}
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
if ([self.delegate respondsToSelector:@selector(thAPITicket:didLoadTicketEvents:response:errorCode:)]) {
if (nil == JSON) {
JSON = @{};
}
[self.delegate thAPITicket:self
didLoadTicketEvents:NO
response:@{@"response" : response, @"json" : JSON}
errorCode:TH_API_ERR_TICKETINDEX_NO_ERROR];
[LCSharedInstance hideNetworkActivity];
}
//Network indicator off
[LCSharedInstance hideNetworkActivity];
}];
[LCSharedInstance showNetworkActivity];
// Send request
[eventsRequest start];
}
URL和我需要的其他数据通过AFNetwork加载,如下所示:
- (id) init
{
if (self = [super init]) {
self.cacheStoreDictionary = [NSMutableDictionary new];
}
return self;
}
- (void) startLoadingImageWithUrl:(NSString *)urlString forItem:(id)item
{
if (self.cacheStoreDictionary[urlString]) {
UIImage *image = self.cacheStoreDictionary[urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:YES];
} else {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
UIImage *image = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
[self.cacheStoreDictionary setObject:image forKey:urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:NO];
});
});
}
}
- (void)fetchTicketEvents
{
// Login URL
NSURL *eventsURL = [NSURL URLWithString:TH_API_BASEURL];
AFHTTPClient *httpClient = [[AFHTTPClient alloc] initWithBaseURL:eventsURL];
httpClient.parameterEncoding = AFJSONParameterEncoding;
// Set request parameters
NSDictionary *params = nil;
NSMutableURLRequest *request = [httpClient requestWithMethod:@"GET"
path:TH_API_PATH_TICKET_EVENT_INDEX
parameters:params];
request.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
// Prepare request
AFJSONRequestOperation *eventsRequest = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
if ([self.delegate respondsToSelector:@selector(thAPITicket:didLoadTicketEvents:response:errorCode:)]) {
NSArray *jsonEventArray = JSON;
NSMutableArray *event = [[NSMutableArray alloc] initWithCapacity:jsonEventArray.count];
for (NSDictionary *eventDictionary in [JSON allObjects]) {
[event addObject:[LCEvent eventFromDictionary:eventDictionary]];
}
[self.delegate thAPITicket:self
didLoadTicketEvents:YES
response:@{@"response" : response, @"json" : JSON, @"event" : event}
errorCode:TH_API_ERR_TICKETINDEX_NO_ERROR];
#if LOG_NETWORKING
[self printJSON:JSON];
#endif
//Network indicator off
[LCSharedInstance hideNetworkActivity];
//Allow Slide-To-Refresh
[LCSharedInstance singletone].allowSlideToRefresh = YES;
[LCSharedInstance singletone].isShownLoadingMessage = NO;
[LCSharedInstance singletone].isLoading = NO;
}
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
if ([self.delegate respondsToSelector:@selector(thAPITicket:didLoadTicketEvents:response:errorCode:)]) {
if (nil == JSON) {
JSON = @{};
}
[self.delegate thAPITicket:self
didLoadTicketEvents:NO
response:@{@"response" : response, @"json" : JSON}
errorCode:TH_API_ERR_TICKETINDEX_NO_ERROR];
[LCSharedInstance hideNetworkActivity];
}
//Network indicator off
[LCSharedInstance hideNetworkActivity];
}];
[LCSharedInstance showNetworkActivity];
// Send request
[eventsRequest start];
}
以下是我如何填充TableViewCell:
- (void) lcCachedImageLoader:(LCCachedImageLoader *)cachedImageLoader didLoadImage:(UIImage *)teaserImage forItem:(id)item wasCacheHit:(BOOL)wasCacheHit
{
//Teaser Image Implementation
UIImageView *imageView = ((UIImageView*)[((UIView*)item)viewWithTag:100]);
imageView.alpha = 0.2;
imageView.image = teaserImage;
imageView.contentMode = UIViewContentModeScaleToFill;
[UIView animateWithDuration:0.5 animations:^{
imageView.alpha = 1.0;
}];
}
#pragma mark - tableview delegation
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"offerCell";
LCEvent *event = self.eventArray[indexPath.row];
tableView = self.tableView;
LCClusterViewController *clusterVC = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
#pragma mark - Cell Config and Style Attributes
clusterVC.titleLabel.attributedText = LCAttrText(event.titleString, LCFontStyleEventName);
clusterVC.ticketDetailsLabel.attributedText = LCAttrText(event.subtitleString, LCFontStyleEventTitle);
clusterVC.oldPriceLabel.attributedText = LCAttrText(event.oldPriceString, LCFontStyleEventOldPrice);
clusterVC.actualPriceLabel.attributedText = LCAttrText(event.actualPriceString, LCFontStyleEventPrice);
clusterVC.timeLabel.attributedText = LCAttrText(event.timeString, LCFontStyleEventInfoText);
clusterVC.ticketCountLabel.attributedText = LCAttrText(event.stockString, LCFontStyleEventInfoText);
clusterVC.dateLabel.attributedText = LCAttrText(event.dateString, LCFontStyleEventDateText);
... and on and on
因此,感谢您提供的任何有用提示您只需编写此代码,在其中指定图像(如果未加载图像),然后
cell.imageView.image = Nil;
如果它已加载,则在if-else中指定图像,如下所示
cell.imageView.image = Nil;
if([dictionary objectForKey:@"Image"])
{
cell.imageView.image = [dictionary objectForKey:@"Image"];
}else
{
cell.imageView.image = Nil;
}
出于性能原因,正在重用表视图单元格,因此,如果在加载图像之前未将其设置为任何值,它们将在UIImageView中保留以前使用的图像 在调用startLoadingImageWithUrl之前,可以先使用占位符图像设置imageView的初始图像,或者在imageView顶部添加加载指示器。但请记住在加载真实图像时移除加载指示器
- (void) startLoadingImageWithUrl:(NSString *)urlString forItem:(id)item
{
UIImageView *imageView = ((UIImageView*)[((UIView*)item)viewWithTag:100]);
imageView.image = placeholderImage;
if (self.cacheStoreDictionary[urlString]) {
UIImage *image = self.cacheStoreDictionary[urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:YES];
} else {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
UIImage *image = [UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
[self.cacheStoreDictionary setObject:image forKey:urlString];
[self.delegate lcCachedImageLoader:self didLoadImage:image forItem:item wasCacheHit:NO];
});
});
}
}
对于加载图像后出现在错误单元格中的图像,这是因为您正在传递项,该项是重复使用的单元格,作为StartLoadImage和didLoadImage中的参数。尝试传递indexPath,并使用indexPath(更新单元格图像视图)找到正确的单元格
UITableViewCell*cell=[self.tableView cellforrowatinexpath:indexath]代码>是的,我也试过了,但它使整个图像加载变慢,并没有真正解决问题。某些图像在短时间内仍处于错误位置。您将startLoadingImageWithUrl:(NSString*)urlString forItem:(id)item称为何处?在我的CellForRowatineXpath末尾:尝试在CellForRowatineXpath中较早地设置占位符图像?是的,我也尝试过;)它的工作效率提高了50%,但仍然有一点错误的图像错误的细胞问题。