How can I animate a content switch in an NSImageView?

Question

I want to switch the image shown in an NSImageView, but I want to animate that change. I've tried various methods to do this. Hopefully one of you could suggest one that might actually work. I'm working with Cocoa for Mac.

Answer 1

As far as I know, NSImageView doesn't support animating image changes. However, you can place a second NSImageView on top of the first one and animate hiding the old one and showing the new one. For example:

NSImageView *newImageView = [[NSImageView alloc] initWithFrame: [imageView frame]];
[newImageView setImageFrameStyle: [imageView imageFrameStyle]];
// anything else you need to copy properties from the old image view
// ...or unarchive it from a nib

[newImageView setImage: [NSImage imageNamed: @"NSAdvanced"]];
[[imageView superview] addSubview: newImageView
                       positioned: NSWindowAbove relativeTo: imageView];
[newImageView release];

NSDictionary *fadeIn = [NSDictionary dictionaryWithObjectsAndKeys:
             newImageView, NSViewAnimationTargetKey,
             NSViewAnimationFadeInEffect, NSViewAnimationEffectKey,
             nil];
NSDictionary *fadeOut = [NSDictionary dictionaryWithObjectsAndKeys:
             imageView, NSViewAnimationTargetKey,
             NSViewAnimationFadeOutEffect, NSViewAnimationEffectKey,
             nil];
NSViewAnimation *animation = [[NSViewAnimation alloc] initWithViewAnimations:
              [NSArray arrayWithObjects: fadeOut, fadeIn, nil]];
[animation setAnimationBlockingMode: NSAnimationBlocking];
[animation setDuration: 2.0];
[animation setAnimationCurve: NSAnimationEaseInOut];
[animation startAnimation];
[imageView removeFromSuperview];
imageView = newImageView;
[animation release];

If your view is big and you can require 10.5+, then you could do the same thing with Core Animation, which will be hardware accelerated and use a lot less CPU.

After creating newImageView, do something like:

[newImageView setAlphaValue: 0];
[newImageView setWantsLayer: YES];
// ...
[self performSelector: @selector(animateNewImageView:) withObject: newImageView afterDelay: 0];

- (void)animateNewImageView:(NSImageView *)newImageView;
{
    [NSAnimationContext beginGrouping];
    [[NSAnimationContext currentContext] setDuration: 2];
    [[newImageView animator] setAlphaValue: 1];
    [[imageView animator] setAlphaValue: 0];
    [NSAnimationContext endGrouping];
}

You'll need to modify the above to be abortable, but I'm not going to write all your code for you :-)

Answer 2

You could implement your own custom view that uses a Core Animation CALayer to store the image. When you set the contents property of the layer, the image will automatically smoothly animate from the old image to the new one.