问题
I have the below menu style layout that mimics facebook. I would like to have a dropshadow on the left side like below however the code I am using with layer shadows makes the application LAGGY. I have not been able to find a good alternative solution. Does anyone have an alternative for creating a dropshadow that does not affect application performance?
[self.navController.view.layer setShadowOffset:CGSizeMake(0, 1)];
[self.navController.view.layer setShadowColor:[[UIColor darkGrayColor] CGColor]];
[self.navController.view.layer setShadowRadius:8.0];
[self.navController.view.layer setShadowOpacity:0.8];
The above code is the code I am currently using that causes application performance issues.
The below image is what I would like to achieve but without having to use the above code.
回答1:
It should help to specify a shadow path, e.g.,
CGPathRef shadowPath = [UIBezierPath bezierPathWithRect:self.navController.view.layer.bounds].CGPath;
[self.navController.view.layer setShadowPath:shadowPath]
According to the CALayer documentation, "Specifying an explicit path usually improves rendering performance."
回答2:
You can just inset the views bounds and set the shadow path:
UIEdgeInsets contentInsets = UIEdgeInsetsMake(10, 0, 0, 0);
CGRect shadowPathExcludingTop = UIEdgeInsetsInsetRect(self.bounds, contentInsets);
self.layer.shadowPath = [UIBezierPath bezierPathWithRect:shadowPathExcludingTop].CGPath;
回答3:
I for myself would just add a UIView containing that shadow as a subview and reposition it as soon as the view on the right side is animated. (e.g. draw that shadow with layers or core graphics)
来源：https://stackoverflow.com/questions/9336187/ios-create-one-sideded-dropshadow