iOS中类似微信红点显示功能

#import <UIKit/UIKit.h>
@interface UIView (CHRRedDot)
@property (readonly, nonatomic) CALayer * chr_redDotLayer;
/**
 红点圆心的位置，与各个边之间的距离。如果距离<=0，则忽略距离
 */
@property (nonatomic, assign) UIEdgeInsets chr_redDotEdgeInsets;
/**
 红点的半径，默认为4
 */
@property (nonatomic, assign) CGFloat chr_redDotRadius;
/**
 红点的颜色，默认为0xFF5A5A
 */
@property (nonatomic, strong) UIColor * chr_redDotColor;
/**
 红点是否显示
 */
@property (nonatomic, assign) BOOL chr_redDotShow;
@end
#pragma mark - method
- (void)chr_updateRedDot {
  CALayer *redDot = self.chr_redDotLayer;
  if (self.chr_redDotShow) {
    if (redDot == nil) {
      redDot = [CALayer layer];
      self.chr_redDotLayer = redDot;
      [self.layer addSublayer:redDot];
    }
    redDot.backgroundColor = self.chr_redDotColor.CGColor;
    [self chr_layoutRedDot];
  } else {
    [redDot removeFromSuperlayer];
    self.chr_redDotLayer = nil;
  }
}
- (void)chr_layoutRedDot {
  CALayer *redDot = self.chr_redDotLayer;
  if (redDot == nil) return;
  CGFloat radius = self.chr_redDotRadius;
  redDot.cornerRadius = radius;
  UIEdgeInsets edgeInsets = self.chr_redDotEdgeInsets;
  CGFloat originX = edgeInsets.right <= 0 ? edgeInsets.left - radius : self.bounds.size.width - edgeInsets.right + radius;
  CGFloat originY = edgeInsets.bottom <= 0 ? edgeInsets.top - radius : self.bounds.size.height - edgeInsets.bottom + radius;
  CGFloat length = radius * 2;
  redDot.frame = CGRectMake(originX, originY, length, length);
}