需求：

需要实现虚线功能

实现方法：

方法一：
使用贝塞尔曲线实现

- (void)addBorderToLayer:(UIView *)view
{
    CAShapeLayer *border = [CAShapeLayer layer];
    //  线条颜色
    border.strokeColor = [UIColor lightGrayColor].CGColor;
    
    border.fillColor = nil;
    
    
    UIBezierPath *pat = [UIBezierPath bezierPath];
    [pat moveToPoint:CGPointMake(0, 0)];
if (CGRectGetWidth(view.frame) > CGRectGetHeight(view.frame)) {
    [pat addLineToPoint:CGPointMake(view.bounds.size.width, 0)];
}else{
    [pat addLineToPoint:CGPointMake(0, view.bounds.size.height)];
}
    border.path = pat.CGPath;
    
    border.frame = view.bounds;
    
    // 不要设太大 不然看不出效果
    border.lineWidth = 0.5;
    border.lineCap = @"butt";
    
    //  第一个是 线条长度   第二个是间距    nil时为实线
    border.lineDashPattern = @[@6, @10];
    
    [view.layer addSublayer:border];
}

方法二：
Quartz 2D绘制

- (void)addBorderToLayer2:(UIView *)view
{
    
    
    
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    [shapeLayer setBounds:view.bounds];
    [shapeLayer setPosition:CGPointMake(CGRectGetWidth(view.frame) / 2, CGRectGetHeight(view.frame)/2)];
    
    [shapeLayer setStrokeColor:[UIColor lightGrayColor].CGColor];
    [shapeLayer setLineWidth:0.5];
    //  设置线宽，线间距
    [shapeLayer setLineDashPattern:@[@6,@10]];
    //  设置路径
    CGMutablePathRef path = CGPathCreateMutable();
    CGPathMoveToPoint(path, NULL, 0, 0);
    if (CGRectGetWidth(view.frame) > CGRectGetHeight(view.frame)) {
        CGPathAddLineToPoint(path, NULL, CGRectGetWidth(view.frame),0);
    }else{
        CGPathAddLineToPoint(path, NULL, 0,CGRectGetHeight(view.frame));
    }
    [shapeLayer setPath:path];
    CGPathRelease(path);
    
    //  把绘制好的虚线添加上来
        [view.layer addSublayer:shapeLayer];
}