我创建了一个NSOperationQueue来下载图片（来自Twitter的Cell）：
NSOperationQueue *queue = [[NSOperationQueue alloc]init];
[queue addOperationWithBlock:^{
NSString *ImagesUrl = [[NSString alloc]initWithFormat:@"http://api.twitter.com/1/users/profile_image/%@",[[status objectForKey:@"user"]objectForKey:@"screen_name"]];;
NSURL *imageurl = [NSURL URLWithString:ImagesUrl];
UIImage *img = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageurl]];
[[NSOperationQueue mainQueue]addOperationWithBlock:^{
if (img.size.width == 0 || [ImagesUrl isEqualToString:@"<null>"]) {
[statusCell.imageCellTL setFrame:CGRectZero];
statusCell.imageCellTL.image = [UIImage imageNamed:@"Placeholder"] ;
}else
[statusCell.imageCellTL setImage:img];
这个工作正常，但是当它似乎移动滚动并查看图像仍在加载时，它们会改变几次直到你得到一张照片。
而且我不喜欢时间的诊断资料，所以我想以某种方式在背景中制作NSOperationQueue
也可以展示如何制作一个＆＃34; Imagecache＆＃34;无需下载已下载的图像。
**（状态= Twitter时间轴的NSDictionary）。
编辑：:(所有单元格）
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *CellIdentifier = @"Celulatime";
UITableViewCell *Cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if ( [Cell isKindOfClass:[TimeLineCell class]] ) {
TimeLineCell *statusCell = (TimeLineCell *) Cell;
status = [self.dataSource objectAtIndex:indexPath.row];
statusCell.TextCellTL.text = [status objectForKey:@"text"];
statusCell.NomeCellTL.text = [status valueForKeyPath:@"user.name"];
statusCell.UserCellTL.text = [NSString stringWithFormat:@"@%@", [status valueForKeyPath:@"user.screen_name"]];
NSDate *created_at = [status valueForKey:@"created_at"];
if ( [created_at isKindOfClass:[NSDate class] ] ) {
NSTimeInterval timeInterval = [created_at timeIntervalSinceNow];
statusCell.timeCellTL.text = [self timeIntervalStringOf:timeInterval];
} else if ( [created_at isKindOfClass:[NSString class]] ) {
NSDate *date = [self.twitterDateFormatter dateFromString: (NSString *) created_at];
NSTimeInterval timeInterval = [date timeIntervalSinceNow];
statusCell.timeCellTL.text = [self timeIntervalStringOf:timeInterval];
}
NSString *imageUrlString = [[NSString alloc]initWithFormat:@"http://api.twitter.com/1/users/profile_image/%@",[[status objectForKey:@"user"]objectForKey:@"screen_name"]];;
UIImage *imageFromCache = [self.imageCache objectForKey:imageUrlString];
if (imageFromCache) {
statusCell.imageCellTL.image = imageFromCache;
[statusCell.imageCellTL setFrame:CGRectMake(9, 6, 40, 40)];
}
else
{
statusCell.imageCellTL.image = [UIImage imageNamed:@"TweHitLogo57"];
[statusCell.imageCellTL setFrame:CGRectZero];
[self.imageluckluck addOperationWithBlock:^{
NSURL *imageurl = [NSURL URLWithString:imageUrlString];
UIImage *img = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageurl]];
if (img != nil) {
[self.imageCache setObject:img forKey:imageUrlString];
// now update UI in main queue
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
TimeLineCell *updateCell = (TimeLineCell *)[tableView cellForRowAtIndexPath:indexPath];
if (updateCell) {
[updateCell.imageCellTL setFrame:CGRectMake(9, 6, 40, 40)];
[updateCell.imageCellTL setImage:img];
}
}];
}
}];
}
}
return Cell;
}
答案 0 :(得分：12)
有几点意见：
您可能应该在类中定义NSOperationQueue并在viewDidLoad（以及NSCache）中初始化它，并将操作添加到该队列，而不是创建每个图片都有新的NSOperationQueue。此外，许多服务器限制了每个客户端支持的并发请求数，因此请务必相应地设置maxConcurrentOperationCount。
@interface ViewController ()
@property (nonatomic, strong) NSOperationQueue *imageOperationQueue;
@property (nonatomic, strong) NSCache *imageCache;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
self.imageOperationQueue = [[NSOperationQueue alloc]init];
self.imageOperationQueue.maxConcurrentOperationCount = 4;
self.imageCache = [[NSCache alloc] init];
}
// the rest of your implementation
@end
您的tableView:cellForRowAtIndexPath:应该在启动异步图像加载之前（a）初始化image（因此您不会在那里看到重用单元格中的旧图像）; （b）在更新之前确保单元格仍然可见：
NSString *imageUrlString = [[NSString alloc]initWithFormat:@"http://api.twitter.com/1/users/profile_image/%@",[[status objectForKey:@"user"]objectForKey:@"screen_name"]];;
UIImage *imageFromCache = [self.imageCache objectForKey:imageUrlString];
if (imageFromCache) {
statusCell.imageCellTL.image = imageFromCache;
[statusCell.imageCellTL setFrame: ...]; // set your frame accordingly
}
else
{
statusCell.imageCellTL.image = [UIImage imageNamed:@"Placeholder"];
[statusCell.imageCellTL setFrame:CGRectZero]; // not sure if you need this line, but you had it in your original code snippet, so I include it here
[self.imageOperationQueue addOperationWithBlock:^{
NSURL *imageurl = [NSURL URLWithString:imageUrlString];
UIImage *img = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageurl]];
if (img != nil) {
// update cache
[self.imageCache setObject:img forKey:imageUrlString];
// now update UI in main queue
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
// see if the cell is still visible ... it's possible the user has scrolled the cell so it's no longer visible, but the cell has been reused for another indexPath
TimeLineCell *updateCell = (TimeLineCell *)[tableView cellForRowAtIndexPath:indexPath];
// if so, update the image
if (updateCell) {
[updateCell.imageCellTL setFrame:...]; // I don't know what you want to set this to, but make sure to set it appropriately for your cell; usually I don't mess with the frame.
[updateCell.imageCellTL setImage:img];
}
}];
}
}];
}
不需要对UIApplicationDidReceiveMemoryWarningNotification进行特殊处理，因为虽然NSCache没有响应此内存警告，但它会在内存不足时自动驱逐其对象。
我没有测试过上面的代码，但希望你能得到这个想法。这是典型的模式。您的原始代码检查了[ImagesUrl isEqualToString:@"<null>"]，我看不出情况如何，但如果除了if (img != nil) ...之外还需要一些额外的逻辑，那么请相应地调整该行。
答案 1 :(得分：1)
Ray Wenderlich的一个很好的例子：http://www.raywenderlich.com/19788/how-to-use-nsoperations-and-nsoperationqueues
如果用户按下取消按钮，它还具有取消功能以取消操作。
答案 2 :(得分：0)
使用swift 3
在tableview中下载异步图像
$(document).ready(function () {
console.log(@Model);
});