Demystifying SwiftUI Previews

Understand how SwiftUI previews work, why they pause, and how to fix it.

Transcript

1. Demystifying SwiftUI previews Marina Gornostaeva | @hybridcattt
2. Agenda ! Other use-cases " Preview lifecycle # The build process $ How live reloading works ⏸ Reduce previews pausing
3. ! Other use-cases
4. ! Other use-cases
5. " Lifecycle of a SwiftUI preview • Build once • Live reload on changes • Pause if change is unsupported by live reloading • Repeat
6. # Build process • For DEBUG • Detect by ENABLE_PREVIEWS build setting • Use ProcessInfo in runtime
7. $ Dynamic replacement • Swift feature called @_dynamicReplacement • Pitched in 2018 • Supports changes in implementation of a function, computed variable, initializer or subscript struct MyStruct { dynamic func x() { print("x") } } extension MyStruct { @_dynamicReplacement(for: x()) func y() { print("y - replaced dynamically") } }
8. $ Limitations of live reloading • It’s applied to everything in the current ile • Supported: changes to bodies of functions, properties, initializers • Not supported: • Editing comments • Signature changes • Adding/removing types, functions, properties • Initial value changes • Changes in other iles
9. ⏸ Improving live reloading • Use computed vars • Check build scripts • Auto-resume previews
10. Thanks & @hybridcattt https://hybridcattt.com/blog/ ixing-swiftui-previews