如何解决的UITableView缓慢滚动 - 使用YouTube API

Question

我与谷歌的YouTube API的工作，和我使用这个代码在这里http://pastebin.com/vmV2c0HT

减慢下来代码中发现这是一个在这里 cell.imageView.image = [UIImage imageWithData:data];

当我删除这些代码是顺利滚动。任何想法如何我可以从谷歌加载图像，但仍然顺利滚动？我读过一些关于以不同的方式加载图像的答案，但我仍然想不通我怎么会让我与正在使用的代码工作。

任何帮助将不胜感激。

贝娄是完整的代码。

#import "RootViewController.h" 

@interface RootViewController (PrivateMethods) 
- (GDataServiceGoogleYouTube *)youTubeService; 
@end 


@implementation RootViewController 

@synthesize feed; 

- (void)viewDidLoad { 
    NSLog(@"loading"); 

    GDataServiceGoogleYouTube *service = [self youTubeService]; 

    NSString *uploadsID = kGDataYouTubeUserFeedIDUploads; 
    NSURL *feedURL = [GDataServiceGoogleYouTube youTubeURLForUserID:@"BmcCarmen" 
                 userFeedID:uploadsID]; 



    [service fetchFeedWithURL:feedURL 
        delegate:self 
      didFinishSelector:@selector(request:finishedWithFeed:error:)]; 

    [super viewDidLoad];  
} 

- (void)request:(GDataServiceTicket *)ticket 
finishedWithFeed:(GDataFeedBase *)aFeed 
      error:(NSError *)error { 

    self.feed = (GDataFeedYouTubeVideo *)aFeed; 

    [self.tableView reloadData]; 


} 


#pragma mark Table view methods 

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { 
    return 1; 
} 






// Customize the number of rows in the table view. 
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { 
    return [[feed entries] count]; 
} 


// Customize the appearance of table view cells. 
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    static NSString *CellIdentifier = @"Cell"; 

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
    if (cell == nil) { 
     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease]; 
    } 

    // Configure the cell. 
    GDataEntryBase *entry = [[feed entries] objectAtIndex:indexPath.row]; 
    NSString *title = [[entry title] stringValue]; 
    NSArray *thumbnails = [[(GDataEntryYouTubeVideo *)entry mediaGroup] mediaThumbnails]; 

    cell.textLabel.text = title; 

    NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[thumbnails objectAtIndex:0] URLString]]]; 
    cell.imageView.image = [UIImage imageWithData:data]; 

    return cell; 
} 

- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    return 100.0f; 
} 




- (void)dealloc { 

    [super dealloc]; 
} 


- (GDataServiceGoogleYouTube *)youTubeService { 
    static GDataServiceGoogleYouTube* _service = nil; 

    if (!_service) { 
     _service = [[GDataServiceGoogleYouTube alloc] init]; 


     [_service setShouldCacheDatedData:YES]; 
     [_service setServiceShouldFollowNextLinks:YES]; 
    } 

    // fetch unauthenticated 
    [_service setUserCredentialsWithUsername:nil 
            password:nil]; 

    return _service; 
} 

@end 

Answer 1

GCD是一件美妙的事情。这是我做的：

    - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
    { 
     static NSString *CellIdentifier = @"youTubeCell"; 
     UITableViewCell *cell = nil; 

     cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; 
     if (cell == nil) 
     { 
      cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier]; 
     } 

     // Configure the cell. 
     GDataEntryBase *entry = [[feed entries] objectAtIndex:indexPath.row]; 
     NSString *title = [[entry title] stringValue]; 
     NSArray *thumbnails = [[(GDataEntryYouTubeVideo *)entry mediaGroup] mediaThumbnails]; 

     cell.textLabel.text = title; 
     // Load the image with an GCD block executed in another thread 
     dispatch_queue_t downloadQueue = dispatch_queue_create("image downloader", NULL); 
     dispatch_async(downloadQueue, ^{ 
      NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:[[thumbnails objectAtIndex:0] URLString]]]; 
      UIImage * image = [UIImage imageWithData:data]; 

      dispatch_async(dispatch_get_main_queue(), ^{    
       cell.imageView.image = image; 
       cell.imageView.contentMode = UIViewContentModeScaleAspectFit; 
       [cell setNeedsLayout]; 
      }); 
     }); 
     dispatch_release(downloadQueue); 

     return cell; 
    } 

滚动现在非常流畅。唯一的缺点是，当你快速地滚动，细胞被重新使用，有时图像的改变，因为新进来了。