Get image width and height before loading it completely in iPhone

问题

I am loading an image in my UITableViewCell using

[NSData dataWithContentsOfURL:imageUrl]

For setting custom height for my tableview cell , i need the actual size of the image that am loading.

Can we get the width and height of an image before loading it completely ? Thanks in advance.

回答1:

NSData is an "opaque" data, so you cannot do much with it before converting it to something more "useful" (e.g., creating an UIImage by means of it -initWithData: method). At that moment you could enquiry the image size, but it would be late for you.

The only approach I see, if you really need knowing the image size before the image is fully downloaded, is implementing a minimal server-side API so that you can ask for the image size before trying to download it.

Anyway, why do you need to know the image size before it is actually downloaded? Could you not set the row height at the moment when it has been downloaded (i.e., from your request delegate method)?

回答2:

you can do it like this:

NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];
UIImage *image = [UIImage imageWithData:imageData];
NSLog(@"image height: %f",image.size.height);
NSLog(@"image width: %f",image.size.width);

回答3:

Take a look at this Question How do I extract the width and height of a PNG from looking at the header in objective c which shares how is it possible to parse image Meta-data.

I have a created OpenSource project Ottran that extracts the image size and type of a remote image by downloading as little as possible, which supports PNG, JPEG , BMP and GIF formats.

回答4:

Try the Image I/O interface as done below. This will allow you to get the image size without having to load the entire file:

#import <ImageIO/ImageIO.h>

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);
NSLog(@"PixelHeight %@",[imageHeader objectForKey:@"PixelHeight"]);

回答5:

dataWithContentsOfURL is synchronous it will block your UI until its download complete, so please use header content to get resolution, Below is Swift 3.0 code

 if let imageSource = CGImageSourceCreateWithURL(url! as CFURL, nil) {
     if let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as Dictionary? {
          let pixelWidth = imageProperties[kCGImagePropertyPixelWidth] as! Int
          let pixelHeight = imageProperties[kCGImagePropertyPixelHeight] as! Int
          print("the image width is: \(pixelWidth)")
          print("the image height is: \(pixelHeight)")
       }
   }

来源：https://stackoverflow.com/questions/6468747/get-image-width-and-height-before-loading-it-completely-in-iphone

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