一个layer可以跟着画完的线移动ios程序 好玩啊。

@interface ViewController ()
@property(nonatomic,assign)CGMutablePathRef path;//添加一个可变路径
@property(nonatomic,strong)CALayer *rectLayer;//添加画图子层
@property(nonatomic,strong)CALayer *drawLayer;//添加画线子层
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    
    //对划线的自曾进行相应的设计
    _drawLayer = [[CALayer alloc]init];
    _drawLayer.bounds = self.view.bounds;
    _drawLayer.position = self.view.layer.position;
    _drawLayer.anchorPoint = self.view.layer.anchorPoint;
    
    //设置drawLayer的代理为自己  让代理进行画图设置及画图的工作
    self.drawLayer.delegate = self;
    [self.view.layer addSublayer:_drawLayer];
    
    
    //对子层进行初始化
    _rectLayer = [[CALayer alloc]init];
    _rectLayer.backgroundColor = [[UIColor yellowColor]CGColor];
    //大小
    _rectLayer.bounds = CGRectMake(0, 0, 30, 30);
    //墙上的位置
    _rectLayer.position = CGPointMake(100, 100);
    
    [self.view.layer addSublayer:_rectLayer];
    
    
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //创建一个可变的path
    _path = CGPathCreateMutable();

    //获得当前点 并将当前点设置为path的开始点
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];
    CGPathMoveToPoint(_path, nil, location.x, location.y);
    
    
}
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    if(_path)
    {
        //获得当前点 并将点添加到path中
        UITouch *touch = [touches anyObject];
        CGPoint location = [touch locationInView:self.view];
        CGPathAddLineToPoint(_path, nil, location.x, location.y);
        
        [self.drawLayer setNeedsDisplay];
    }
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    
    /*
     在触摸结束的时候开始一个动画  当然了这个动画效果就是图片层的移动
     首先应该创建一个动画帧 动画  
     然后设置相应的参数
     最后给要设置的涂层加上动画
     */
    CAKeyframeAnimation *keyFrameA = [[CAKeyframeAnimation alloc]init];
    //持续时间是3秒
    keyFrameA.duration = 6.0f;
    //设置 keyPath（指定的接受动画的关键路径 也就是点）
    keyFrameA.keyPath = @"position";
    //设置 path （基于点的属性的路径）
    keyFrameA.path = self.path;
    
    //设置图能够留在最后的位置
    keyFrameA.removedOnCompletion = NO;
    keyFrameA.fillMode = kCAFillModeForwards;
    
    //相应的添加动画
    [self.rectLayer addAnimation:keyFrameA forKey:@"keyFrame"];
    if(_path)
    {
        //释放path
        CGPathRelease(_path);
    }
}

#pragma mark-实现caLayer的代理方法
-(void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx
{
    CGContextAddPath(ctx, _path);//将path加入到ctx中
    
    //设置花臂的颜色
    CGContextSetStrokeColorWithColor(ctx, [[UIColor redColor]CGColor]);
    
    CGContextDrawPath(ctx, kCGPathStroke);//设置值描边不填充
}