问题
I want to achieve the effect of fade in / fade out the rect or text. I call CGContextFillRect or CGContextShowText in my UIVIew's drawRect: method. I wonder if there is a way to achieve the animation without using UIView' support(i.e. [UIView beginAnimations::]. The desired effect I want to achieve is similar to what in Microsoft's bing serach engine, like those small black squares fade in/ fade out as you move around the web page. Thanks in advance!
回答1:
Why do you not want to use UIView's animation blocks? Animating a change in opacity of a view (UILabel or otherwise) with that is pretty easy. For example, the following code will fade out a given view over a duration of 0.5 seconds:
[UIView beginAnimations:nil context:NULL];
[UIView setAnimationDuration:0.5f];
viewToFadeOut.alpha = 0.0f;
[UIView commitAnimations];
To fade in, simply replace the alpha value of 0.0f with 1.0f.
You can do the same using a manually constructed CABasicAnimation, manipulating the UIView's layer:
CABasicAnimation *fadeOutAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
fadeOutAnimation.duration = 0.5f;
fadeOutAnimation.removedOnCompletion = NO;
fadeOutAnimation.fillMode = kCAFillModeForwards;
fadeOutAnimation.toValue = [NSNumber numberWithFloat:0.0f];
[viewToFadeOut.layer addAnimation:fadeOutAnimation forKey:@"animateOpacity"];
If all you want to do is fade in / out a border around a view, try animating the borderColor property of the UIView's layer (same as the above CABasicAnimation, only replacing opacity with borderColor and the toValue with a CGColor cast to id).
来源：https://stackoverflow.com/questions/1939841/how-do-i-fade-in-out-a-rectangle-or-text