如何在单片机中获取图像文件的图像大小而不加载它？

Question

How to get the image size of an image file in monotouch without loading it in memory?

I tried to use CGImageSource from the MonoTouch.ImageIO namespace, as indicated in the Apple documentation and in this blog post:

oleb.net

But this code doesn't work:

public Size GetImageSizeFromImageFile (string image_file_path)
    {

        CGImageSource imageSource = CGImageSource.FromUrl (NSUrl.FromFilename (image_file_path));

        if (imageSource == null) {
            // Error loading image
            Console.WriteLine ("Error loading image info for file: " + image_file_path);
            return Size.Empty;
        }

        NSDictionary imageProperties = new NSDictionary ();
        imageSource.CopyProperties (imageProperties, 0);

        int width = (int)imageProperties.ValueForKey (new NSString ("kCGImagePropertyPixelWidth"));
        int height = (int)imageProperties.ValueForKey (new NSString ("kCGImagePropertyPixelHeight"));


        Console.WriteLine (@"Image " + image_file_path + " dimensions: " + width + " x " + height+" px");

        imageProperties.Dispose ();

        return new Size(width, height);
    }

Casting to strings doesn't make any difference, the field returns empty.

Any help is appreciated, thanks!

Answer 1

The latest MonoTouch releases makes it a lot easier to get the image properties using the new GetProperties method. Eg

using (var src = CGImageSource.FromUrl (NSUrl.FromFilename (filename))) {
    CGImageOptions options = new CGImageOptions () { ShouldCache = false };
    // do not forget the '0' image index or you won't get what you're looking for!
    using (var p = src.GetProperties (options, 0)) {
        Console.WriteLine ("{0}x{1}", p.PixelWidth, p.PixelHeight);
    }
}

Answer 2

Looks like this is a bug in Mono Touch. I tested the code in XCode with the same image in Mono Touch and it worked in XCode.

In Mono Touch after calling the imageSource.CopyProperties(imageProperties,0) imageProperties.Keys Count is 0

So you should create a bug report at bugzilla.xamarin.com/