onAppear

`onAppear(handler)`

Parameter	Type	Description
`handler`	`() => void`	Function to call when the view appears.

Adds an onAppear modifier that calls a function when the view appears.

Returns: ModifierConfig

See: Official SwiftUI documentation.

You can add onAppear to any view. It changes what you see on 33 of the 39 components.

It works on these components, but not in the way that you may expect.

Component	What to know
BottomSheet	Runs for the anchor, not for the sheet. To know when the sheet opens, put it on a view in the sheet content.
Alert	Runs for the trigger, not for the alert.
ConfirmationDialog	Runs for the trigger, not for the dialog.
Popover	Runs for the trigger, not for the popover. To know when the popover opens, put it on a view in `Popover.Content`.
TabView	Runs for the whole tab view, not for one tab. Put it on the content of a tab.

These components accept it, but you see no change.

Component	Why nothing happens
Spacer	In SDK 57, Spacer does not send modifier events to JavaScript, so the handler does not run.
Divider	In SDK 57, Divider does not send modifier events to JavaScript, so the handler does not run.
Slider	In SDK 57, Slider does not send modifier events to JavaScript, so the handler does not run.
Menu	In SDK 57, Menu does not send modifier events to JavaScript, so the handler does not run.
ContextMenu	In SDK 57, ContextMenu does not send modifier events to JavaScript, so the handler does not run.
AccessoryWidgetBackground	In SDK 57, AccessoryWidgetBackground does not send modifier events to JavaScript, so the handler does not run.

The original Expo docs for this page:

onAppear (Modifiers) (source-of-truth/versions/v57.0.0/sdk/ui/swift-ui/modifiers.md)