问题
So I am doing some custom animations on my navigationcontroller and the way it pushes and pops the viewControllers.
Everything runs smooth. As soon as I add the following code (In a subclass of UINavigationController), I face a huge performance hit. After adding a shadow all animations become very laggy. Is this expected or am I doing something wrong in the code?
// This code gets called once during NavigationController initialization.
[self.view setClipsToBounds:NO];
[self.view.layer setCornerRadius:5];
[self.view.layer setShadowOffset:CGSizeMake(0, 20)];
[self.view.layer setShadowColor:[[UIColor yellowColor] CGColor]];
[self.view.layer setShadowRadius:20.0];
[self.view.layer setShadowOpacity:1];
EDIT:
Changed my shadow radius to 1 and it's still slow
回答1:
You should expect a slowdown from adding a shadow. A shadowRadius of 20 is very high and will be especially slow.
The other key to improve shadow rendering speed: set the shadowPath property. It can help dramatically.
回答2:
self.view.layer.shouldRasterize = YES;
self.view.layer.rasterizationScale = UIScreen.mainScreen.scale;
I was recently having some issues with slow CALayer shadows, and that simple line of code fixed up everything for me!
回答3:
Using shadowPath instead of shadowOffset.
theView.layer.shadowPath = [UIBezierPath bezierPathWithRect:theView.bounds].CGPath;
Check this post: iphone - Animation's performance is very poor when view's shadow is on
回答4:
Yes, shadow's are very expensive (especially a shadow that big -- play with the radius and you'll notice it makes a huge difference in the degree of slowdown you experience). One way to improve performance is to render it once to a CGImageContext and just display that image instead of having the layer re-render the shadow every time it redraws (but this doesn't work if the shadow needs to animate or something).
来源：https://stackoverflow.com/questions/9997972/calayer-shadow-causes-a-performance-hit