Q:

Animate path of shape layer

I'm stumped by what I thought would be a simple problem.
I'd like to draw views connected by lines, animate the position of the views and have the connecting line animate too.  I create the views, and create a line between them like this:
- (UIBezierPath *)pathFrom:(CGPoint)pointA to:(CGPoint)pointB {
    CGFloat halfY = pointA.y + 0.5*(pointB.y - pointA.y);
    UIBezierPath *linePath=[UIBezierPath bezierPath];
    [linePath moveToPoint: pointA];
    [linePath addLineToPoint:CGPointMake(pointA.x, halfY)];
    [linePath addLineToPoint:CGPointMake(pointB.x, halfY)];
    [linePath addLineToPoint:pointB];
    return linePath;
}

-(void)makeTheLine {
    CGPoint pointA = self.viewA.center;
    CGPoint pointB = self.viewB.center;

    CAShapeLayer *lineShape = [CAShapeLayer layer];
    UIBezierPath *linePath=[self pathFrom:pointA to:pointB];
    lineShape.path=linePath.CGPath;

    lineShape.fillColor = nil;
    lineShape.opacity = 1.0;
    lineShape.strokeColor = [UIColor blackColor].CGColor;
    [self.view.layer addSublayer:lineShape];
    self.lineShape = lineShape;
}

It draws just how I want it to.  My understanding from the docs is that I am allowed to animate a shape's path by altering it in an animation block, like this:
- (void)moveViewATo:(CGPoint)dest {
    UIBezierPath *destPath=[self pathFrom:dest to:self.viewB.center];
    [UIView animateWithDuration:1 animations:^{
        self.viewA.center = dest;
        self.lineShape.path = destPath.CGPath;
    }];
}

But no dice.  The view position animates as expected, but the line connecting to the other view "jumps" right away to the target path.
This answer implies that what I'm doing should work.  And this answer suggests a CABasic animation, which seems worse to me since (a) I'd then need to coordinate with the much cooler block animation done to the view, and (b) when I tried it this way, the line didn't change at all....
// worse way
- (void)moveViewATo:(CGPoint)dest {
    UIBezierPath *linePath=[self pathFrom:dest to:self.viewB.center];
    [UIView animateWithDuration:1 animations:^{
        self.viewA.center = dest;
        //self.lineShape.path = linePath.CGPath;
    }];

    CABasicAnimation *morph = [CABasicAnimation animationWithKeyPath:@"path"];
    morph.duration = 1;
    morph.toValue = (id)linePath.CGPath;
    [self.view.layer addAnimation:morph forKey:nil];
}

Thanks in advance.

A:

Thanks all for the help.  What I discovered subsequent to asking this is that I was animating the wrong property.  It turns out, you can replace the layer's shape in an animation, like this:
CABasicAnimation *morph = [CABasicAnimation animationWithKeyPath:@"path"];
morph.duration  = 1;
morph.fromValue = (__bridge id)oldPath.path;
morph.toValue   = (__bridge id)newPath.CGPath;
[line addAnimation:morph forKey:@"change line path"];
line.path=linePath.CGPath;

