iPhone - How to make a circle path for a CAKeyfram

问题:

I'm trying to make an key frame animation that lets a image view fly around a circle. I'm using CGPathAddCurveToPoint to make the key frame points. The problem is that the image view always uses the shortest (linear) route.

I would like to have some kind of function that builds a circle path for a given radius.

Thanks a lot for any help.

回答1:

CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, startPoint.x, startPoint.y);
CGPathAddQuadCurveToPoint(path, NULL,middlePoint.x, middlePoint.y,endPoint.x,endPoint.y);

CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
pathAnimation.removedOnCompletion = NO;
pathAnimation.path = path;
[pathAnimation setCalculationMode:kCAAnimationCubic];
[pathAnimation setFillMode:kCAFillModeForwards];
pathAnimation.duration = 2.0;

[viewTobemoved.layer addAnimation:pathAnimation forKey:nil];

This animation uses only one bezier point and makes a soft circle from beginning point to end point.If you want to define the curve exactly by also defining the radius of the circle you can refer to the following link

http://blog.shoguniphicus.com/2011/05/19/keyframe-animation-ios-cakeyframeanimation-objective-c/

回答2:

Would this do the trick?

  CAKeyframeAnimation* circlePathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"center"];

  CGMutablePathRef circularPath = CGPathCreateMutable();
  CGRect pathRect = ...; // some rect you define. A circle has equal width/height; radius is half the values you specify here
  CGPathAddEllipseInRect(circularPath, NULL, pathRect);
  spinAnimation.path = circularPath;
  CGPathRelease(circularPath);

You will notice the keypath of the animation is the center property of the UIView you wish to make fly around in a circle.