这里我将展示如何在UIView上让对象沿着路径动画，我将创建路径并画到UIView上让你能都看见，并沿相同的路径来做动画。
我在添加到屏幕的UIView完成所有的这些…
首先，我们在屏幕上画一条曲线
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//Thisdrawsaquadraticbeziercurvedlinerightacrossthescreen
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-(
void
)drawACurvedLine{
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//Createabitmapgraphicscontext,youwilllatergetaUIImagefromthis
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UIGraphicsBeginImageContext(CGSizeMake(320,460));
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CGContextRefctx=UIGraphicsGetCurrentContext();
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//Setvariablesinthecontextfordrawing
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CGContextSetLineWidth(ctx,1.5);
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CGContextSetStrokeColorWithColor(ctx,[UIColorwhiteColor].CGColor);
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//Setthestartpointofyourdrawing
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CGContextMoveToPoint(ctx,10,10);
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//Theendpointofthelineis310,450....i'malsosettingareferencepointof10,450
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//Aquadraticbeziercurveisdrawnusingthesecoordinates-experimentandseetheresults.
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CGContextAddQuadCurveToPoint(ctx,10,450,310,450);
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//Addanothercurve,theoppositeoftheabove-finishingbackwherewestarted
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CGContextAddQuadCurveToPoint(ctx,310,10,10,10);
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//Drawtheline
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CGContextDrawPath(ctx,kCGPathStroke);
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//GetaUIImagefromthecurrentbitmapcontextwecreatedatthestartandthenendtheimagecontext
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UIImage*curve=UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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//Withtheimage,weneedaUIImageView
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UIImageView*curveView=[[UIImageViewalloc]initWithImage:curve];
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//Settheframeoftheview-whichisusedtopositionitwhenweaddittoourcurrentUIView
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curveView.frame=CGRectMake(1,1,320,460);
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curveView.backgroundColor=[UIColorclearColor];
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[selfaddSubview:curveView];
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}
现在我我创建了一个关键帧动画，并添加一个和我们话得线一样的路径。我们还将画一个圈，并沿着路径做动画:
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-(
void
)animateCicleAlongPath{
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//Preparetheanimation-weusekeyframeanimationforanimationsofthiscomplexity
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CAKeyframeAnimation*pathAnimation=[CAKeyframeAnimationanimationWithKeyPath:@
"position"
];
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//Setsomevariablesontheanimation
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pathAnimation.calculationMode=kCAAnimationPaced;
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//Wewanttheanimationtopersist-notsoimportantinthiscase-butkeptforclarity
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//Ifweanimatedsomethingfromlefttoright-andwewantedittostayinthenewposition,
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//thenwewouldneedtheseparameters
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pathAnimation.fillMode=kCAFillModeForwards;
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pathAnimation.removedOnCompletion=NO;
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pathAnimation.duration=5.0;
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//Letsloopcontinuouslyforthedemonstration
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pathAnimation.repeatCount=1000;
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//Setupthepathfortheanimation-thisisverysimilarasthecodethedrawtheline
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//insteadofdrawingtothegraphicscontext,insteadwedrawlinesonaCGPathRef
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CGPointendPoint=CGPointMake(310,450);
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CGMutablePathRefcurvedPath=CGPathCreateMutable();
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CGPathMoveToPoint(curvedPath,NULL,10,10);
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CGPathAddQuadCurveToPoint(curvedPath,NULL,10,450,310,450);
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CGPathAddQuadCurveToPoint(curvedPath,NULL,310,10,10,10);
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//Nowwehavethepath,wetelltheanimationwewanttousethispath-thenwereleasethepath
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pathAnimation.path=curvedPath;
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CGPathRelease(curvedPath);
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//Wewillnowdrawacircleatthestartofthepathwhichwewillanimatetofollowthepath
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//Weusethesametechniqueasbeforetodrawtoabitmapcontextandtheneventuallycreate
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//aUIImageViewwhichweaddtoourview
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UIGraphicsBeginImageContext(CGSizeMake(20,20));
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CGContextRefctx=UIGraphicsGetCurrentContext();
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//Setcontextvariables
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CGContextSetLineWidth(ctx,1.5);
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CGContextSetFillColorWithColor(ctx,[UIColorgreenColor].CGColor);
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CGContextSetStrokeColorWithColor(ctx,[UIColorwhiteColor].CGColor);
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//Drawacircle-andpaintitwithadifferentoutline(white)andfillcolor(green)
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CGContextAddEllipseInRect(ctx,CGRectMake(1,1,18,18));
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CGContextDrawPath(ctx,kCGPathFillStroke);
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UIImage*circle=UIGraphicsGetImageFromCurrentImageContext();
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UIGraphicsEndImageContext();
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UIImageView*circleView=[[UIImageViewalloc]initWithImage:circle];
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circleView.frame=CGRectMake(1,1,20,20);
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[selfaddSubview:circleView];
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//AddtheanimationtothecircleView-onceyouaddtheanimationtothelayer,theanimationstarts
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[circleView.layeraddAnimation:pathAnimationforKey:@
"moveTheSquare"
];
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}
要让所有的都跑起来，你可以使用init函数：
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-(id)initWithFrame:(CGRect)frame{
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if
(self=[superinitWithFrame:frame]){
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[selfdrawACurvedLine];
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[selfanimateCicleAlongPath];
-
}
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return
self;
-
}
在你的ViewController中像这样写
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-(
void
)viewDidLoad{
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UIView*customView=[[Canvasalloc]initWithFrame:CGRectMake(0,0,320,460)];
-
customView.backgroundColor=[UIColorblackColor];
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[self.viewaddSubview:customView];
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[customViewrelease];
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[superviewDidLoad];
-
}
还有，不要忘记添加 Quartz 引用:
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#import<QuartzCore/QuartzCore.h>
我确定有很多更好的方式来做这个事，例如使用CALayers 和添加CGImage 到layers。但是那是一些我没有尝试的东西。上面的例子应该足够让你开始沿着路径做动画。
这里是工程拷贝http://blog.devedup.com/wp-content/uploads/2010/06/AnimateAlongAPath.zip
（译者水平有限，欢迎指正。）
