[iphone] How to rotate image around center point automatically with finger touch

Question

On iPhone, how to implement rotating image around the center point using finger touch ?

Just like wheel, if you put finger on the iPhone screen , then move suddenly, then the image becoming rotating around center point just like the wheel, after a while, it becomes more and more slow , finally stop.

Who can help to give some pieces of codes (Object-C) or some suggest ?

Answer 1

I would use the affine transformations - yuou can assign a transformation to any layer or UI element using the transform property.

You can create a rotation transform using CGAffineTransform CGAffineTransformMakeRotation( CGFloat angle) which will return a transformation that rotates an element. The default rotation should be around the centerpoint.

Be aware, the rotation is limited to 360 degrees, so if you want to rotate something more than that (say through 720 degrees) - you have to break the rotation into several sequences.

You may find this SO article useful as well.

Answer 2

The transform property of a view or layer can be used to rotate the image displayed within. As far as the spinning part goes, you just track the location and movement of touches in your view with touchesBegan, touchesMoved, and touchesEnded.

Use the distance and time between the touches updates to calculate a speed, and use that to set a rotational velocity. Once you start the image spinning, update the position periodically (with an NSTimer, maybe), and reduce the rotational velocity by some constant.

Answer 3

This question is similar to what you're asking.