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IOS 获取网络图片大小实例详解

时间:2021-03-18 15:45     来源/作者:菁欣

IOS 获取网络图片大小实例详解

 在iOS开发过程中经常需要通过网络请求加载图片,有时,需要在创建UIImageView或UIButton来显示图片之前需要提前知道图片的尺寸,根据图片尺寸创建对应大小的控件。但是对于网络图片来说,要想通过最优的方法获得尺寸就略微有点困难,大体思路就是下面这种:

如果有使用SDWebImage,则首先检查是否缓存过该图片,如果没有,先通过文件头获取图片大小(针对格式为png、gif、jpg文件获取其尺寸大小),如果获取失败,则下载完整的图片data,然后计算大小,如果有使用SDWebImage,则使用SDWebImage缓存该图片。

实例代码:

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+(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;
 
    }
 
  }
 
}

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原文链接:http://www.cnblogs.com/jingxin1992/p/6150438.html

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