SwiftUI Scroll Performance: The 120FPS Challenge

Squeezing high performance from the magic

SwiftUI is like magic.

But, like all well-designed magic systems, it comes with a cost.

What, you thought that beautiful declarative syntax and automatic data bindings come free? Think again.

Swift’s pesky memory safety mechanisms put it at a performance disadvantage compared to unsafe languages like C and C++. In the same way, SwiftUI’s beautiful reactive data-flow gobbles CPU cycles like an Ozempic patient at the hot-dog eating contest.

To achieve the maximum 120Hz refresh rate, the main thread has to execute all layout computation and rendering in 8.3ms to avoid a frame drop: the dreaded hitch. With system overhead, you’re lucky to get 5ms for this work.

SwiftUI can run into very painful performance problems when dealing with infinite scrolling feeds. Today, we will investigate these performance problems, understand why they happen, and explore techniques to mitigate them, making your SwiftUI performance buttery smooth 🧈.

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