设置虚线

在自定义view中

 - (instancetype)initWithFrame:(CGRect)frame {
    if (self == [super initWithFrame:frame]) {
        CAShapeLayer *border = [CAShapeLayer layer];
        
        border.strokeColor = [UIColor redColor].CGColor;
        
        border.fillColor = nil;
        
        border.path = [UIBezierPath bezierPathWithRect:self.bounds].CGPath;
        
        border.frame = self.bounds;
        
        border.lineWidth = 1.f;
        
        border.lineCap = @"square";
        
        border.lineDashPattern = @[@4, @4];    //可以修改查看不同效果
        
        [self.layer addSublayer:border];
    }
    return self;
}```


当不是在 

• (instancetype)initWithFrame:(CGRect)frame;

 方法
而是在 

• (instancetype)init;

我是这样写

• (instancetype)init {
  if (self == [super init]) {
  }
  return self;
  }

• (void)layoutIfNeeded {
  [super layoutIfNeeded];
  CAShapeLayer *border = [CAShapeLayer layer];

  border.strokeColor = [UIColor redColor].CGColor;

  border.fillColor = nil;

  border.path = [UIBezierPath bezierPathWithRect:self.bounds].CGPath;

  border.frame = self.bounds;

  border.lineWidth = 1.f;

  border.lineCap = @"square";

  border.lineDashPattern = @[@4, @4];

  [self.layer addSublayer:border];

}

在创建 CustonView的时候

CustonView *view = [[CustonView alloc] init];//WithFrame:CGRectMake(100, 100, 100, 100)];
view.frame = CGRectMake(100, 100, 100, 100);
[view layoutIfNeeded];
[self.view addSubview:view];