refresher

Project to play around with using a custom spinner for a UIRefreshControl.

Requirements

• Cocoapods
• Xcode 11 or higher

To run, please execute: pod install

Then build in Xcode

Outcomes/learnings

• I initially used a subview to make a custom spinner for UIRefreshControl. I used a two step animation to spin the image 180 degrees, then another 180 degrees. Only after a full rotation, do we check for an exit condition. This gives the animation an odd, jerky kind of motion. Like it always snaps into a stationary position before sliding off the screen.
• To correct this, I rewrote the class to use layers instead of views. CAKeyframeAnimation(keyPath: "transform.rotation") with a repeatCount of infinity gives a nice smooth animation, as shown in the demo GIF above.
• But here I ran into the limitations of subclassing UIRefreshControl. Basically, endRefreshing() is not a good place to do the end-of-lifecycle events I wanted because it actually gets triggered while the refresh control is still on the screen. If I want to remove the layer and it's animation, I ideally need a method that happens after the control has left the screen. But UIRefreshControl has no override point for this.
• Since I had no good place to remove the layer, I had to make sure it only got added to the view once, even if the user pulls to refresh multiple times to avoid a leak.
• I also found I had to call beginRefreshing() explicitly once I overrode it, or it wouldn't get triggered. Still not sure why that is.
• Given these limitations, it might be worthwhile subclassing UIControl instead of UIRefreshControl to get more explicit control over the lifecycle.