iOS 对象沿着指定路径进行动画

以下方法可作为两步实现：
    以下方法在自定义view的类里面实现，可放在自定义函数中自行控制触法。也可放在drawRect或layoutSubviews里面让view在显 示时触法。但推荐放在自定义view中触发，因为这样才可以做到自行控制，并保证同时只有一个在运行，否则会因为view的改变导致重绘，导致同时执行多 个相同的动画，会影响效果和耗费内存。

    一》让view对象沿指定的路径进行动画的方法：

  以下是指定路径：
    CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    //Set some variables on the animation
    pathAnimation.calculationMode = kCAAnimationPaced;
    //We want the animation to persist - not so important in this case - but kept for clarity
    //If we animated something from left to right - and we wanted it to stay in the new position,
    //then we would need these parameters
    pathAnimation.fillMode = kCAFillModeForwards;
    pathAnimation.removedOnCompletion = NO;
    pathAnimation.duration = 10;
    //Lets loop continuously for the demonstration
    pathAnimation.repeatCount = 10;

  //Setup the path for the animation - this is very similar as the code the draw the line
    //instead of drawing to the graphics context, instead we draw lines on a CGPathRef
    //CGPoint endPoint = CGPointMake(310, 450);
    CGMutablePathRef curvedPath = CGPathCreateMutable();
    CGPathMoveToPoint(curvedPath, NULL, 10, 10);
    CGPathAddQuadCurveToPoint(curvedPath, NULL, 10, 450, 310, 450);
    CGPathAddQuadCurveToPoint(curvedPath, NULL, 310, 10, 10, 10);

  //Now we have the path, we tell the animation we want to use this path - then we release the path
    pathAnimation.path = curvedPath;
    CGPathRelease(curvedPath);

    在指定路径后，指定动画的对象，（在此用UIImageView举例：）
    UIImageView *circleView = [[UIImageView alloc] initWithImage:circle];
    circleView.frame = CGRectMake(1, 1, 40, 40);
    [self addSubview:circleView];

    //Add the animation to the circleView - once you add the animation to the layer, the animation starts
    [circleView.layer addAnimation:pathAnimation
    forKey:@"moveTheSquare"];

    二>.若要把指定的路径以线条或其他方法显示出来，则要绘制路径，方法是：

  UIGraphicsBeginImageContext(CGSizeMake(320,460));
    CGContextRef ctx = UIGraphicsGetCurrentContext();

//Set variables in the context for drawing
    CGContextSetLineWidth(ctx, 1.5);
    CGContextSetStrokeColorWithColor(ctx, [UIColor whiteColor].CGColor);

//Set the start point of your drawing
    CGContextMoveToPoint(ctx, 10, 10);
    //The end point of the line is 310,450 .... i'm also setting a reference point of 10,450
    //A quadratic bezier curve is drawn using these coordinates - experiment and see the results.
    CGContextAddQuadCurveToPoint(ctx, 10, 450, 310, 450);
    //Add another curve, the opposite of the above - finishing back where we started
    CGContextAddQuadCurveToPoint(ctx, 310, 10, 10, 10);

//Draw the line
    CGContextDrawPath(ctx, kCGPathStroke);

    若要绘制图片背景（直接添加即可），则：
    //With the image, we need a UIImageView
    UIImage *image = [UIImage imagewithName:@"a.png"];
    UIImageView *curveView = [[UIImageView alloc] image];
    //Set the frame of the view - which is used to position it when we add it to our current UIView
    curveView.frame = CGRectMake(1, 1, 320, 460);
    curveView.backgroundColor = [UIColor greenColor];
    [self addSubview:curveView];