如何使用CAKeyframeAnimation为CoreGraphics绘制形状的动画

Question

我试图在UIView子类中为UIBeizerPath（在我的示例中为三角形）绘制动画。但是，整个子视图是动画而不是形状。

动画中是否有我遗漏的东西？

- (void)drawRect:(CGRect)rect {

   CAShapeLayer *drawLayer = [CAShapeLayer layer];

   drawLayer.frame           = CGRectMake(0, 0, 100, 100);
   drawLayer.strokeColor     = [UIColor greenColor].CGColor;
   drawLayer.lineWidth       = 4.0;

   [self.layer addSublayer:drawLayer];

   UIBezierPath *path = [UIBezierPath bezierPath];

  [path moveToPoint:CGPointMake(0,0)];
  [path addLineToPoint:CGPointMake(50,100)];
  [path addLineToPoint:CGPointMake(100,0)];
  [path closePath];

  CGPoint center = [self convertPoint:self.center fromView:nil];

  [path applyTransform:CGAffineTransformMakeTranslation(center.x, center.y)];

  [[UIColor redColor] set];

  [path fill];

  [[UIColor blueColor] setStroke];

  path.lineWidth = 3.0f;

  [path stroke];

  CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];

  pathAnimation.duration        = 4.0f;
  pathAnimation.path            = path.CGPath;
  pathAnimation.calculationMode = kCAAnimationLinear;

  [drawLayer addAnimation:pathAnimation forKey:@"position"];
}