IB_DESIGNABLE for UIButton Failed to render instance - ios

Question

I create a category of UIButton class, use IB_DESIGNABLE. But I got an strange error Failed to render instance of RoundedCornerButton: Rendering the view took longer than 200 ms. Your drawing code may suffer from slow performance. I tried many suggestions on this website but still cannot fix it. please help me to find the root cause.Please see the image for more detail (RoundedCornerButton: is the category of UIButton class)
Update: the code for RoundedCornerButton class:
.h file
#import <UIKit/UIKit.h>
IB_DESIGNABLE
#interface RoundedCornerButton : UIButton
#property (nonatomic) IBInspectable int cornerRadius;
#property (nonatomic) IBInspectable int borderWidth;
#property (nonatomic) IBInspectable UIColor* borderColor;
#end
.m file:
#import "RoundedCornerButton.h"
#implementation RoundedCornerButton
-(void)drawRect:(CGRect)rect{
self.layer.borderWidth = self.borderWidth;
self.layer.borderColor = self.borderColor.CGColor;
[self.layer setCornerRadius:self.cornerRadius];
self.clipsToBounds = YES;
}
#end
I can run my project on device successful, but I got the Red warning as above.(It so strange, I use Xcode 7.0)

Answer 1

You mustn't play with your layer in drawRect like that. That isn't drawing! Drawing is about content.
Move that code somewhere else, such as awakeFromNib and prepareForInterfaceBuilder (both), and all will be well.
Here's example code:
#implementation RoundedCornerButton
-(void) config {
self.layer.borderWidth = self.borderWidth;
self.layer.borderColor = self.borderColor.CGColor;
[self.layer setCornerRadius:self.cornerRadius];
self.clipsToBounds = YES;
}
-(void)prepareForInterfaceBuilder {
[self config];
}
-(void)awakeFromNib {
[super awakeFromNib];
[self config];
}
#end
And you can see it works fine in IB in Xcode 7: