How to fade out a NSView with animation?

For those looking for a Swift version instead:

NSAnimationContext.runAnimationGroup({ context in
    context.duration = 1
    self.view.animator().alphaValue = 0
}, completionHandler: {
    self.view.isHidden = true
    self.view.alphaValue = 1
})

For layer-backed views, this is enough:

view.animator().isHidden = true

For those already on Swift 5.3 or above, you can leverage the new Multiple Trailing Closures syntax sugar here for an even cleaner version:

NSAnimationContext.runAnimationGroup { context in
    context.duration = 1
    self.view.animator().alphaValue = 0
} completionHandler: {
    self.view.isHidden = true
    self.view.alphaValue = 1
}

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;