Scripting
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Getting Started
Documentation
Changelog
Privacy

Lifecycle Events

Scripting supports SwiftUI-style lifecycle hooks onAppear and onDisappear to execute custom logic when a view becomes visible or is removed from the visible interface. These hooks allow you to trigger animations, start data loading, update state, or perform cleanup when views enter or exit the screen.

Property Definitions

1onAppear?: () => void
2onDisappear?: () => void

Property Descriptions

Property Type Description
onAppear () => void Called every time the view becomes visible. This includes the initial appearance and reappearance after being temporarily obscured (e.g., when dismissing a sheet). Executed before the first rendered frame.
onDisappear () => void Called every time the view is no longer visible on screen. This includes temporary disappearance (e.g., when presenting a sheet over the view).

Example

1import { VStack, Text, useState } from "scripting"
2
3function Example() {
4  const [message, setMessage] = useState("")
5
6  return <VStack
7    onAppear={() => setMessage("View is visible")}
8    onDisappear={() => setMessage("View is hidden")}
9    padding
10  >
11    <Text>{message}</Text>
12  </VStack>
13}

Behavior Notes

  • Unlike UIKit’s viewDidAppear and viewDidDisappear, which are tied to the navigation stack or full-screen view controller lifecycle, Scripting's onAppear and onDisappear are called every time the view appears or disappears from the screen.

  • For example:

    • If you present a sheet, the background view’s onDisappear is triggered.
    • When the sheet is dismissed, the background view’s onAppear is triggered again.

  • These events are not called only once, but every time visibility changes, making them well-suited for observing the view’s active presence in the UI.

Use Cases

  • onAppear:

    • Start loading data
    • Begin animations
    • Reset UI state when shown

  • onDisappear:

    • Stop timers
    • Cancel requests
    • Save form data
Outline