Tween between radial gradients

I am new to Objective C for iOS programming, so please be nice :-).

I have an app in Android (Java) app that I want to port to iOS. In Android I have 3 radial gradient backgrounds (red-black, green-black, blue-black) defined in an XML shape and I can easily transform between the 3 in a loops animation.

I want to do the same in iOS.

So far I have read about:

CAGradientLa开发者_如何学Cyer, CAGradient, CGGradient

..and I'm utterly confused.

Can somebody explain what and how is the best way to animate between 3 radial gradients, and does this need to be coded or using PNG's ?

Thanks

I did eventually solve this, using the built in animation function to change the View's background colour from Rad, to Yellow, to Green.

I then made a PNG which was a radial gradient from center alpha 0 to outer black alpha 100.