Rotating a UIView around a center point without rotating the view itself

Question

I would like to rotate a UIView around a center point without rotating the UIView itself. So more like the cars of a ferris wheel (always staying upright) as opposed to the hands of a clock.

The times I've rotated UIViews around a center point, I've used layer position/anchorPoint/transform to accomplish the effect. But that obviously changes the orientation of the view itself.

Any help?

keller

Answer 1

This is pretty easy to do in Core Animation. I've used some pretty boring static values for this example, so obviously you'll want to make some modifications. But this will show you how to move a view along a circular UIBezierPath.

UIView *view = [UIView new];
[view setBackgroundColor:[UIColor redColor]];
[view setBounds:CGRectMake(0.0f, 0.0f, 50.0f, 50.0f)];
[view setCenter:[self pointAroundCircumferenceFromCenter:self.view.center withRadius:140.0f andAngle:0.0f]];
[self.view addSubview:view];

UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(CGRectGetMidX(self.view.frame) - 140.0f, CGRectGetMidY(self.view.frame) - 140.0f, 280.0f, 280.0f)];

CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
pathAnimation.duration = 5.0;

pathAnimation.path = [path CGPath];

[view.layer addAnimation:pathAnimation forKey:@"curveAnimation"];

And a basic function to generate the initial center of the view.

- (CGPoint)pointAroundCircumferenceFromCenter:(CGPoint)center withRadius:(CGFloat)radius andAngle:(CGFloat)theta
{
    CGPoint point = CGPointZero;
    point.x = center.x + radius * cosf(theta);
    point.y = center.y + radius * sinf(theta);

    return point;
}

Answer 2

You should reposition your view's center around a circle over and over again. Implement a method that calculates the current center point and keep calling that method from a UIView animateWithDuration... method.