iOS获取网络图片的大小

【iOS获取网络图片的大小】如何在下载网络图片之前获取图片的大小,以设置图片的frame?
如下:

#import NSMutableString *imageURL = [NSMutableString stringWithFormat:@"http://www.myimageurl.com/image.png"]; CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)[NSURL URLWithString:imageURL], NULL); NSDictionary* imageHeader = (__bridge NSDictionary*) CGImageSourceCopyPropertiesAtIndex(source, 0, NULL); NSLog(@"Image header %@",imageHeader); CGFloat pixelHeight = [[imageHeader objectForKey:@"PixelHeight"] floatValue]; CGFloat pixelWidth= [[imageHeader objectForKey:@"PixelWidth"] floatValue]; CGSize size = CGSizeMake(pixelWidth, pixelHeight);

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