iPhone CALayer动画

我正在绘制一个直线动画，用一条直线连接两个点。这是我的代码：

-(void) drawObject{     
    rootLayer   = [CALayer layer];
    rootLayer.frame = self.view.bounds;
    [self.view.layer addSublayer:rootLayer];

    lineStartPath = CGPathCreateMutable();
    CGPathMoveToPoint(lineStartPath, nil, 160, 50);
    CGPathAddLineToPoint(lineStartPath, nil, 160, 50);
    CGPathCloseSubpath(lineStartPath);

    lineEndPath = CGPathCreateMutable();
    CGPathMoveToPoint(lineEndPath, nil, 160, 50);
    CGPathAddLineToPoint(lineEndPath, nil, 160, 300);
    CGPathCloseSubpath(lineEndPath);

    shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = lineStartPath;
    UIColor *strokeColor = [UIColor colorWithHue:0.557 saturation:0.55 brightness:0.96 alpha:1.0];
    shapeLayer.strokeColor = strokeColor.CGColor;
    shapeLayer.lineWidth = 3.0;

    [rootLayer addSublayer:shapeLayer];

    [self performSelector:@selector(startAnimation) withObject:nil afterDelay:1.0];
}

-(void) startAnimation{
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"path"];
    animation.duration = 0.5;
    animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    animation.fromValue = (id)lineStartPath;
    animation.toValue = (id)lineEndPath;
    [shapeLayer addAnimation:animation forKey:@"animatePath"];
}

弱点是动画结束后，线消失。我希望在这两点之间画一条线之后，id不会消失。请给我一个提示。

尝试添加

shapeLayer.path = lineEndPath;

在

开始动画的开头

这段视频对此进行了解释：来自WWDC 2010（大约38:00）

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并替换

[shapeLayer addAnimation:animation forKey:@“animatePath”]与
[shapeLayer addAnimation:animation forKey:@“path”]
添加动画时，关键点可以是任何您想要的，它仅用于使用
[myLayer animationForKey:@“myKey]”获取动画