Question

This question seems to get asked a lot but I have never found a definitive answer as to whether or not it’s possible to have custom transitions the same way UIKit does.

I know you can do tricks like take a screenshot of the current view and the upcoming view, and then animate those while you change view controllers under the animation. However, this takes quite a bit of memory, as you have basically 2 full extra screens worth of drawing (because of the screenshots).

I’m looking for a more elegant way of presenting view controllers with a custom animation. Or, is there a more memory-efficient way of doing the above approach?

Answer 1

There are several ways to accomplish this, depending on how you want to transition, whether your controllers are embedded in a container controller, etc. In the simplest case, where you have a single controller, and you want to transition to another controller, you can do it with the following steps:

1. instantiate the new controller (lets call it B, and the original one A)
2. add B’s view as a subview of the window (gotten from self.view.window)
3. set B’s frame to be off screen in which ever direction you want or make its alpha 0, or make it have zero size, depending on what kind of transition you want.
4. do what ever transition you want with animateWithDuration:animations:completion:
   remove A’s view (in the completion block)
5. in the completion block, make B the root view controller of the window