看代码

 extension UIView{
    
    /*
     width:虚线的宽度
     length：虚线的长度
     space：虚线间的间距
     cornerRadius：view圆角
     color：虚线的颜色
     */
    func swiftDrawBoardDottedLine(width:CGFloat,
                                  length:CGFloat,space:CGFloat,cornerRadius:CGFloat,color:UIColor){
          self.layer.cornerRadius = cornerRadius
          let borderLayer =  CAShapeLayer()
          borderLayer.bounds = self.bounds
          
          borderLayer.position = CGPoint(x: self.bounds.midX, y: self.bounds.midY);
          borderLayer.path = UIBezierPath(roundedRect: borderLayer.bounds, cornerRadius: cornerRadius).cgPath
          borderLayer.lineWidth = width / UIScreen.main.scale
          
          //虚线边框---小边框的长度
          borderLayer.lineDashPattern = [length,space]  as [NSNumber]? //前边是虚线的长度，后边是虚线之间空隙的长度
          borderLayer.lineDashPhase = 0.1
          //实线边框
          
          borderLayer.fillColor = UIColor.clear.cgColor
          borderLayer.strokeColor = color.cgColor
          self.layer.addSublayer(borderLayer)
     }
}

使用

  override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .brown
        let v = UIView.init(frame: CGRect.init(x: 100, y:200 , width: 240, height: 80))
        v.backgroundColor = .gray
        v.swiftDrawBoardDottedLine(width: 3,length: 7, space: 4, cornerRadius: 8, color: .white)
        view.addSubview(v)
    }

效果图如下：

举个例子假如你要给 uicollectionviewcell 添上边框：

- (void)awakeFromNib {

    [superawakeFromNib];

    self.layer.borderColor=[[UIColorgrayColor]CGColor];

    self.layer.borderWidth=1;

}

如果给cell 里的控件加圆角

则 要加上 XXX.layer.maskToBouds=yes;