UIImageView  *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];

    imageView.backgroundColor = [UIColor redColor];
    [self.view addSubview:imageView];
// 線的路徑
    UIBezierPath *polygonPath = [UIBezierPath bezierPath];
    
    // 這些點(diǎn)的位置都是相對于所在視圖的
    // 起點(diǎn)
    [polygonPath moveToPoint:CGPointMake(25, 5)];
    // 其他點(diǎn)
    [polygonPath addLineToPoint:CGPointMake(15, 15)];
    [polygonPath addLineToPoint:CGPointMake(25, 25)];
    
//    [polygonPath closePath]; // 添加一個(gè)結(jié)尾點(diǎn)和起點(diǎn)相同
    
    CAShapeLayer *polygonLayer = [CAShapeLayer layer];
    polygonLayer.lineWidth = 3;
    polygonLayer.strokeColor = [UIColor whiteColor].CGColor;
    polygonLayer.path = polygonPath.CGPath;
    polygonLayer.fillColor = nil; // 默認(rèn)為blackColor
    [imageView.layer addSublayer:polygonLayer];

參考鏈接:https://www.cnblogs.com/jaesun/p/iOS-CAShapeLayerUIBezierPath-hua-xian.html