UILabel 划线动画

Question

有这么一个需求，需要在UILabel Text上点击之后添加划线效果，就是类似todo done那种。
我知道简单的划线就是起点加重点坐标，连接成为一条线，但是如何用代码控制看到由点到线的效果呢？

CGContextSetLineWidth(context, 1);
CGContextMoveToPoint(context, x, y);
CGContextAddLineToPoint(context, x, y);
CGContextStrokePath(context);

谢谢！

Answer 1

代码在这里：https://github.com/driventokill/DelLi...
主要是这两个方法：

- (void)setupLayers
{
    if (animationLayer != nil) {
        [animationLayer removeFromSuperlayer];
    }
    animationLayer = [CALayer layer];
    animationLayer.frame = self.bounds;
    [self.layer addSublayer:animationLayer];
    
    CGPoint midLeft = CGPointMake(CGRectGetMinX(animationLayer.bounds), CGRectGetMidY(animationLayer.bounds));
    CGPoint midRight = CGPointMake(CGRectGetMaxX(animationLayer.bounds), CGRectGetMidY(animationLayer.bounds));
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:midLeft];
    [path addLineToPoint:midRight];
    
    pathLayer = [CAShapeLayer layer];
    pathLayer.frame = animationLayer.bounds;
    pathLayer.geometryFlipped = YES;
    pathLayer.path = path.CGPath;
    pathLayer.strokeColor = [UIColor blackColor].CGColor;
    pathLayer.lineWidth = 2;
    [animationLayer addSublayer:pathLayer];
}

- (void)startAnimation
{
    [animationLayer removeAllAnimations];
    [pathLayer removeAllAnimations];
    
    CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
    pathAnimation.duration = 3.0;
    pathAnimation.fromValue = [NSNumber numberWithFloat:0.0f];
    pathAnimation.toValue = [NSNumber numberWithFloat:1.0f];
    [pathLayer addAnimation:pathAnimation forKey:@"strokeEnd"];
}