How to fade out a NSView with animation?

The modern approach is much easier:

[NSAnimationContext runAnimationGroup:^(NSAnimationContext *context) {
    context.duration = 1;
    view.animator.alphaValue = 0;
}
completionHandler:^{
    view.hidden = YES;
    view.alphaValue = 1;
}];

If the view hierarchy is layer-backed, it’s actually sufficient to do:

view.animator.hidden = YES;