As ever, thanks very much David. I figured there was *something* going on when
drawRect: was defined but I wouldn't have figured out what without this help.
In this case a crossfade in every case for that particular view works
perfectly, I implemented what you suggested and it looks so much better, it's
amazing the difference that even a .3-.5 second smooth transition can make,
just takes the edge off something which was quite harsh before, looks much more
professional.
Got the point (again) on using simple subviews when possible, a mistake I've
made before. In this particular case I don't think that was going to work, but
I'm very happy with what I have now.
Andreas, thanks for your reply too. You had pretty much exactly the same
thoughts I did and we both tried the same ideas, with the same
..AllowAnimatedContent etc and got the same results; hope David's reply was
useful to you too, it goes in my 'keepers' file.
On 03-Mar-2011, at 5:10 AM, David Duncan wrote:
> On Mar 2, 2011, at 5:12 AM, Roland King wrote:
>
>> I was trying to animate the backgroundColor of one of my UIView subclasses
>> yesterday using
>>
>> [ UIView animateWithDuration:2.0 animations:^{ [ myView
>> setBackgroundColor:someColor ]; } ];
>>
>> but no matter what the duration set, the background color was changing
>> instantly. Whilst looking to see if there were two places I called
>> setBackgroundColor: (there weren't) I realized that my UIView subclass has
>> its own drawRect: method (this view is basically a piece of paper with some
>> lines drawn on it, so it needs a custom drawRect: method). Commenting that
>> out, the view background animated properly, but of course I had no content.
>> Even just adding an empty drawRect: method was enough to defeat the
>> animation.
>
>
> When you implement -drawRect:, the background color of your view is then
> drawn into the associated CALayer, rather than just being set on the CALayer
> as a style property. Now Core Animation can animate both transitions, but
> UIView disables the animation of a layer's contents, which thus prevents you
> from getting a contents crossfade (as in the vast majority of cases this
> wouldn't be what you want).
>
> The crossfade may be exactly what you want in this case. Likely the best way
> to defeat UIView's override in this case may be to create a subclass of
> CALayer that overrides -actionForKey:. In that override, you would check for
> the @"contents" key and return a CABasicAnimation ([CABasicAnimation
> animation] should do it) and in all other cases return what the default
> implementation does. This has the downside that you will *always* cross fade
> and you won't be able to integrate with UIKit's animation APIs (you just get
> animation for contents on all the time).
>
> Another solution would be to use a super view that contains just the
> background color and have your lines composited over it (assuming they are
> simple lines this could be done with simple subviews that are sized for each
> line). This would allow you to avoid -drawRect: entirely, which would allow
> you to animate the background color and may offer some memory usage benefits
> (if you can use subviews).
> --
> David Duncan
>
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