在后台加载图像以优化ios中的加载

我试图优化我的应用程序的负载，实际上，我有很多图像加载在我的应用程序，我花了很多时间等待视图控制器打开，特别是第一个初始视图，其中包括很多的图像。

我看了一下苹果样品

但我不能重新工作整个应用程序，我想要的只是具体告诉我该怎么办？

在tableview ，cell的实现cellforrowatindexpath:

  NSURL *imageURL = ......; NSData *imageData = [NSData dataWithContentsOfURL:imageURL]; UIImage *imageLoad; imageLoad = [[UIImage alloc] initWithData:imageData]; imageView.image = imageLoad; 

我可以做些什么吗？

感谢您的帮助！

Answer 1

是的，你可以添加占位符图像。

它不会减慢滚动速度，并随着时间的推移加载图像。

还导入这个文件UIImageView + WebCache.m和MapKit框架

这里是下载文件的链接 。

 - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier]; } UIImageview* iV = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 50, 50)]; [iV setImageWithURL:[NSURL URLWithString:url] placeholderImage:[UIImage imageNamed:@"image_placeholder.gif"]]; [cell.contentView addSubview:iV]; [iV release]; } 

只要清理，build立和运行。

Answer 2

试试这个代码：

 dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); dispatch_async(q, ^{ /* Fetch the image from the server... */ NSData *data = [NSData dataWithContentsOfURL:url]; UIImage *img = [[UIImage alloc] initWithData:data]; dispatch_async(dispatch_get_main_queue(), ^{ /* This is the main thread again, where we set the tableView's image to be what we just fetched. */ cell.imgview.image = img; }); }); 

Answer 3

在从服务器获取图像时启用应用程序，并在加载图像时禁用块尝试使用UIImageView + AFNetworking库asynchronous加载服务器的图像AFNetworking

  NSString *imageUrl = [[dict objectForKey:@"photo"] objectForKey:@"url"]; UIImageView *myImage = [[UIImageView alloc] init]; [myImage setImageWithURL:[NSURL URLWithString:imageUrl] placeholderImage:[UIImage imageNamed:@"PlaceHolder.png"]]; 

只需添加这个库，并包含UIImageView + AFNetworking，以便您可以使用新的UIImageView类别imageWithUrl

Answer 4

看看这个控制： https ： //github.com/nicklockwood/AsyncImageView

这很容易实现（只有1个头文件），并将适合您的需要就好了。

使用此控件：而不是声明：

 NSURL *imageURL = ......; NSData *imageData = [NSData dataWithContentsOfURL:imageURL]; UIImage *imageLoad; imageLoad = [[UIImage alloc] initWithData:imageData]; imageView.image = imageLoad; 

使用：

 NSURL *imageURL = ......; imageView.imageURL = imageURL; 

Answer 5

你可以查看NSOperationQueue上的这个教程，这个在GCD上完全一样。 你也可以尝试使用：

 // Block variable to be assigned in block. __block NSData *imageData; dispatch_queue_t backgroundQueue = dispatch_queue_create("com.razeware.imagegrabber.bgqueue", NULL); // Dispatch a background thread for download dispatch_async(backgroundQueue, ^(void) { imageData = [NSData dataWithContentsOfURL:imageURL]; UIImage *imageLoad; imageLoad = [[UIImage alloc] initWithData:imageData]; // Update UI on main thread dispatch_async(dispatch_get_main_queue(), ^(void) { imageView.image = imageLoad; }); }); 

Answer 6

你可以尝试这样的事情！

  dispatch_queue_t checkInQueueForPostImage = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); dispatch_async(checkInQueueForPostImage, ^{ UIImage *image = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:postAndCheckInDetails.postImageURL]]]; dispatch_sync(dispatch_get_main_queue(), ^{ if (image!=nil) { [uploadImage setImage:image]; } [cell setNeedsLayout]; }); }); 

Answer 7

这里是一个略有修改的方法Ramu Pasupoletis的答案。 我添加了__block修饰符，使var img在主线程中调用的块内可见。 这里是我使用的完整的方法定义

 -(UITableViewCell*)cellforRowAtIndexPath:(UIIndexPath*)indexPath; 

懒惰地提取缩略图。 我还为单元格UIImageView添加了占位符。

 //lazy loading of thumbnails for images in cell via bg thread -(void)loadImageForCell:(CustomEditTableViewCell*)theCell withFilepath: (NSString*)filepath{ dispatch_queue_t q = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); dispatch_async(q, ^{ UIImage (__block *img) = [UIImage imageWithContentsOfFile:filepath]; UIImage *thumbnail = [[GlobalFunctions sharedGlobalFunctions] imageOfSize:CGSizeMake(40, 40) fromImage:img]; dispatch_async(dispatch_get_main_queue(), ^{ theCell.imageView.image = thumbnail; }); }); } 

Answer 8

使用IDAsyncImageView.h

  ////////////////////////////////////// IDAsyncImageView.h ///////////////////////////////////// @interface IDAsyncImageView : NSObject @property (nonatomic, strong) NSCache *cache; + (instancetype)instance; - (void)loadImageView:(UIImageView*)imageView withURLString:(NSString *)urlString; @end ////////////////////////////////////// IDAsyncImageView.m ///////////////////////////////////// #import "IDAsyncImageView.h" @implementation IDAsyncImageView + (instancetype)instance { static IDAsyncImageView *_instance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ _instance = [[self alloc] init]; }); return _instance; } - (instancetype)init { self = [super init]; if (self) { self.cache = [[NSCache alloc] init]; } return self; } - (void)loadImageView:(UIImageView*)imageView withURLString:(NSString *)urlString { UIActivityIndicatorView* activityView; activityView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]; activityView.hidesWhenStopped = YES; activityView.center = CGPointMake(imageView.bounds.size.width / 2.0f, imageView.bounds.size.height / 2.0f); activityView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleBottomMargin; [imageView addSubview:activityView]; [activityView startAnimating]; UIImage* imageLoad = [self.cache objectForKey:urlString]; if (nil != imageLoad) { imageView.image = imageLoad; [activityView removeFromSuperview]; } else { // Block variable to be assigned in block. __block NSData *imageData; // Dispatch a background thread for download dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{ imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]]; UIImage* imageLoad = [[UIImage alloc] initWithData:imageData]; // Update UI on main thread dispatch_async(dispatch_get_main_queue(), ^(void) { [self.cache setObject:imageLoad forKey:urlString]; imageView.image = imageLoad; [activityView removeFromSuperview]; }); }); } } ////////////////////////////////////// ViewController.m ////////////////////////////////////// - (void)viewDidLoad { [super viewDidLoad]; [[IDAsyncImageView instance] loadImageView:myImageView withURLString:aUrl]; } 

Answer 9

您可以使用asynchronousimageview。

 - (void) loadImageFromURL:(NSURL*)url placeholderImage:(UIImage*)placeholder cachingKey:(NSString*)key { self.imageURL = url; self.image = placeholder; NSData *cachedData = [FTWCache objectForKey:key]; if (cachedData) { self.imageURL = nil; self.image = [UIImage imageWithData:cachedData]; return; } dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0ul); dispatch_async(queue, ^{ NSData *data = [NSData dataWithContentsOfURL:url]; UIImage *imageFromData = [UIImage imageWithData:data]; [FTWCache setObject:data forKey:key]; if (imageFromData) { if ([self.imageURL.absoluteString isEqualToString:url.absoluteString]) { dispatch_sync(dispatch_get_main_queue(), ^{ self.image = imageFromData; }); } else { // NSLog(@"urls are not the same, bailing out!"); } } self.imageURL = nil; }); } 

看看这个链接 。你会有一个使用asynchronousimageview的想法。