---
title: "customWindowsToEnterFullScreen(for:on:)"
framework: appkit
role: symbol
role_heading: Instance Method
path: "appkit/nswindowdelegate/customwindowstoenterfullscreen(for:on:)"
---

# customWindowsToEnterFullScreen(for:on:)

Called when the window is about to enter full-screen mode.

## Declaration

```swift
@MainActor optional func customWindowsToEnterFullScreen(for window: NSWindow, on screen: NSScreen) -> [NSWindow]?
```

## Parameters

- `window`: The window to enter full-screen mode.
- `screen`: The display screen on which the window will enter full-screen mode.

## Return Value

Return Value An array of windows to use for the animation to full-screen mode for window; otherwise nil.

## Discussion

Discussion This method lets a window delegate customize the animation when the window is about to enter full-screen mode by providing a custom window or windows containing layers or other effects. If you don’t want to perform custom animation, you can omit the implementation of this method, or it can return nil. Special Considerations If this method and customWindowsToEnterFullScreen(for:) are both implemented, this method is called.

## See Also

### Custom Full-Screen Presentation Animations

- [customWindowsToEnterFullScreen(for:)](appkit/nswindowdelegate/customwindowstoenterfullscreen(for:).md)
- [window(_:startCustomAnimationToEnterFullScreenWithDuration:)](appkit/nswindowdelegate/window(_:startcustomanimationtoenterfullscreenwithduration:).md)
- [window(_:startCustomAnimationToEnterFullScreenOn:withDuration:)](appkit/nswindowdelegate/window(_:startcustomanimationtoenterfullscreenon:withduration:).md)
- [windowDidFailToEnterFullScreen(_:)](appkit/nswindowdelegate/windowdidfailtoenterfullscreen(_:).md)
- [customWindowsToExitFullScreen(for:)](appkit/nswindowdelegate/customwindowstoexitfullscreen(for:).md)
- [window(_:startCustomAnimationToExitFullScreenWithDuration:)](appkit/nswindowdelegate/window(_:startcustomanimationtoexitfullscreenwithduration:).md)
- [windowDidFailToExitFullScreen(_:)](appkit/nswindowdelegate/windowdidfailtoexitfullscreen(_:).md)