---
title: "windowWillResize(_:to:)"
framework: appkit
role: symbol
role_heading: Instance Method
path: "appkit/nswindowdelegate/windowwillresize(_:to:)"
---

# windowWillResize(_:to:)

Tells the delegate that the window is being resized (whether by the user or through one of the setFrame... methods other than setFrame(_:display:)).

## Declaration

```swift
@MainActor optional func windowWillResize(_ sender: NSWindow, to frameSize: NSSize) -> NSSize
```

## Parameters

- `sender`: The window being resized.
- `frameSize`: The size to which the specified window is being resized.

## Return Value

Return Value A custom size to which the specified window will be resized.

## Discussion

Discussion The  frameSize contains the size (in screen coordinates) sender will be resized to. To resize to a different size, simply return the desired size from this method; to avoid resizing, return the current size. sender’s minimum and maximum size constraints have already been applied when this method is called. While the user is resizing a window, the delegate is sent a series of windowWillResize(_:to:) messages as the window’s frame continues to change size.

## See Also

### Sizing Windows

- [windowDidResize(_:)](appkit/nswindowdelegate/windowdidresize(_:).md)
- [windowWillStartLiveResize(_:)](appkit/nswindowdelegate/windowwillstartliveresize(_:).md)
- [windowDidEndLiveResize(_:)](appkit/nswindowdelegate/windowdidendliveresize(_:).md)