IOS 获取网络图片大小实例详解

+(CGSize)downloadImageSizeWithURL:(id)imageURL{  NSURL* URL = nil;  if([imageURL isKindOfClass:[NSURL class]]){    URL = imageURL;  }  if([imageURL isKindOfClass:[NSString class]]){    URL = [NSURL URLWithString:imageURL];  }  if(URL == nil)    return CGSizeZero;#ifdef dispatch_main_sync_safe  if([[SDImageCache sharedImageCache] diskImageExistsWithKey:absoluteString])  {    UIImage* image = [[SDImageCache sharedImageCache] imageFromMemoryCacheForKey:absoluteString];    if(!image)    {      NSData* data = [[SDImageCache sharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:) withObject:URL.absoluteString];      image = [UIImage imageWithData:data];    }    if(image)    {      return image.size;    }  }#endif  NSMutableURLRequest *request = [[NSMutableURLRequest alloc]initWithURL:URL cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:1];    NSString* pathExtendsion = [URL.pathExtension lowercaseString];  CGSize size = CGSizeZero;  if ([pathExtendsion rangeOfString:@"png"].location != NSNotFound) {    size = [self downloadPNGImageSizeWithRequest:request];  }  else if([pathExtendsion rangeOfString:@"gif"].location != NSNotFound)  {    size = [self downloadGIFImageSizeWithRequest:request];  }  else{    size = [self downloadJPGImageSizeWithRequest:request];  }  if(CGSizeEqualToSize(CGSizeZero, size))  {    NSData* data = [NSData dataWithContentsOfURL:URL];    UIImage* image = [UIImage imageWithData:data];    if(image)    {      //如果未使用SDWebImage，则忽略；缓存该图片#ifdef dispatch_main_sync_safe      [[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];#endif      size = image.size;    }  }  //过滤掉不符合大小的图片，大图太大浪费流量，用户体验不好  if (size.height > 2048 || size.height <= 0 || size.width > 2048 || size.width <= 0 ) {    return CGSizeZero;  }  else  {    return size;  }}+(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request{  [request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];  NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];  if(data.length == 8)  {    int w1 = 0, w2 = 0, w3 = 0, w4 = 0;    [data getBytes:&w1 range:NSMakeRange(0, 1)];    [data getBytes:&w2 range:NSMakeRange(1, 1)];    [data getBytes:&w3 range:NSMakeRange(2, 1)];    [data getBytes:&w4 range:NSMakeRange(3, 1)];    int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;    int h1 = 0, h2 = 0, h3 = 0, h4 = 0;    [data getBytes:&h1 range:NSMakeRange(4, 1)];    [data getBytes:&h2 range:NSMakeRange(5, 1)];    [data getBytes:&h3 range:NSMakeRange(6, 1)];    [data getBytes:&h4 range:NSMakeRange(7, 1)];    int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;    return CGSizeMake(w, h);  }  return CGSizeZero;} +(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request{  [request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];  NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];  if(data.length == 4)  {    short w1 = 0, w2 = 0;    [data getBytes:&w1 range:NSMakeRange(0, 1)];    [data getBytes:&w2 range:NSMakeRange(1, 1)];    short w = w1 + (w2 << 8);    short h1 = 0, h2 = 0;    [data getBytes:&h1 range:NSMakeRange(2, 1)];    [data getBytes:&h2 range:NSMakeRange(3, 1)];    short h = h1 + (h2 << 8);    return CGSizeMake(w, h);  }  return CGSizeZero;} +(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request{  [request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];  NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];    if ([data length] <= 0x58) {    return CGSizeZero;  }  if ([data length] < 210) {// 肯定只有一个DQT字段    short w1 = 0, w2 = 0;    [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];    [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];    short w = (w1 << 8) + w2;    short h1 = 0, h2 = 0;    [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];    [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];    short h = (h1 << 8) + h2;    return CGSizeMake(w, h);  } else {    short word = 0x0;    [data getBytes:&word range:NSMakeRange(0x15, 0x1)];    if (word == 0xdb) {      [data getBytes:&word range:NSMakeRange(0x5a, 0x1)];      if (word == 0xdb) {// 两个DQT字段        short w1 = 0, w2 = 0;        [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];        [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];        short w = (w1 << 8) + w2;        short h1 = 0, h2 = 0;        [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];        [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];        short h = (h1 << 8) + h2;        return CGSizeMake(w, h);      } else {// 一个DQT字段        short w1 = 0, w2 = 0;        [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];        [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];        short w = (w1 << 8) + w2;        short h1 = 0, h2 = 0;        [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];        [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];        short h = (h1 << 8) + h2;        return CGSizeMake(w, h);      }    } else {      return CGSizeZero;    }  }}