Question

I have a 400 pattern images at 400×300 bundled within my app. I would like to make some kind of factory method to take a portion of that image and load them into UIImageViews. I’ve had some success with using content mode and clipping to bounds, but when I load a ton of these into a view it can take upwards of 5 seconds for the view to load. Here is an example of my current method.

UIImageView *tinyImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed@"400x300testImage.png"];
[tinyImageView setFrame:CGRectMake(0, 0, 10, 200)];
[tinyImageView setContentMode:UIViewContentModeTopLeft];
[tinyImageView setClipsToBounds:YES];
[self.tinyImagesView addSubview:tinyImageView];

I’ve been reading the ImageIO class files and I think my answer is in there but I’m having a hard time putting together workable code. In another stackoverflow question I came across this code

CFDictionaryRef options = (__bridge CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:
                                                (id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailWithTransform, 
                                                (id)kCFBooleanTrue, (id)kCGImageSourceCreateThumbnailFromImageIfAbsent, 
                                                (id)[NSNumber numberWithFloat:200.0f], (id)kCGImageSourceThumbnailMaxPixelSize, 
                                                nil];
    CGImageRef imgRef = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, options);

    UIImage *scaled = [UIImage imageWithCGImage:imgRef];

    CGImageRelease(imgRef);
    CFRelease(imageSource);

    return scaled;

This has a similar load time to loading the full images and clipping.

Is it possible to read in only a 10×200 strip of an image file and load that into a UIImageView that is as fast as creating that 10×200 png and loading that using imageNamed?

Answer 1

I’m pretty sure what you really want is a CATiledLayer, where you can point it at the set of images and have it automatically pull up what it needs.

You can just add a CATiledLayer to any UIView.