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];