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];