Question

In the iPhone application Roambi, the pie chart shown can be animated to rotate with the user as if rotating a disc. We can hold and do lot of stuff with that.

Someone mentioned that the Roambi app was developed using core-plot library:

What library use Roambi app iPhone to draw chart?

How can I manipulate a pie chart developed using Core plot?

Answer 1

A quick look at the Core Plot source code reveals that CPPieChart‘s inheritance looks like this:

CPPieChart : CPPlot : CPAnnotationHostLayer : CPLayer : CALayer

So you can see that in the end, CPPieChart is just a heavily subclassed CALayer. I might be entirely incorrect here, but there’s nothing that indicates that this can’t be animated like any other CALayer. Try the following code to rotate the layer by 360 degrees:

CABasicAnimation *rotation = [CABasicAnimation animationWithKeyPath:@"transform"];
CATransform3D transform = CATransform3DMakeRotation(DegreesToRadians(360), 0, 0, 1);
rotation.toValue = [NSValue valueWithCATransform3D:transform];
rotation.duration = 10.0f;
[pieChart addAnimation:rotation forKey:@"rotation"];

If you can get this working then its just a matter of reading the values from the accelerometer and converting them to rotation angles.