路径动画CAShapeLayer

的我画四分之一圆。为此，我用UIView的中心作为中心。绘图部分很好。
现在我想让它在路径上动画。所以我使用了KeyFrame动画。
问题是它在CAShapeLayer的中心旋转。我不想要。我想围绕边界旋转cgpath。在初始位置看，这是正确的。但是当开始在路径上旋转时，它正在占据CAShapeLayer的中心，然后在路径上旋转。路径动画CAShapeLayer

这里是黄季代码：

 CGMutablePathRef path = CGPathCreateMutable(); 
    CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100, (0), (M_PI_2), NO); 
    CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100-50, (M_PI_2), (0), YES); 
    CGPathCloseSubpath(path); 
    CAShapeLayer* arcLayer = [[CAShapeLayer alloc]init]; 
    arcLayer.path = path; 
    arcLayer.frame = CGPathGetPathBoundingBox(path); 
    arcLayer.fillColor = [UIColor yellowColor].CGColor; 
    arcLayer.backgroundColor = [UIColor whiteColor].CGColor; 
    arcLayer.bounds = CGPathGetPathBoundingBox(path);

我盯着单水龙头动画gesture.Here是动画代码：

- (void)singleTapGestureCaptured:(UITapGestureRecognizer *)gesture{ 
    CGPoint touchPoint=[gesture locationInView:self]; 
    NSArray* subLayerArray = [pathLayer sublayers]; 
    for (int i = 0; i < subLayerArray.count; i++) { 
    CAShapeLayer* layer = [subLayerArray objectAtIndex:i]; 
    if(CGPathContainsPoint(layer.path, NULL, touchPoint, NO)){ 
     CGMutablePathRef path = CGPathCreateMutable(); 
     CGPathAddArc(path, NULL, self.bounds.size.width/2, self.bounds.size.height/2, 100, 0, 3*M_PI/2, NO); 
     CAKeyframeAnimation *anim = [CAKeyframeAnimation animationWithKeyPath:@"position"]; 
     anim.path = path; 
     anim.rotationMode = kCAAnimationRotateAutoReverse; 
     anim.fillMode = kCAFillModeForwards; 
     anim.removedOnCompletion = NO; 
     anim.duration = 100.0; 
     [layer addAnimation:anim forKey:@""]; 
     } 
    } 
    }

Initial postion during rotaion