---
title: "size(forChildContentContainer:withParentContainerSize:)"
framework: uikit
role: symbol
role_heading: Instance Method
path: "uikit/uicontentcontainer/size(forchildcontentcontainer:withparentcontainersize:)"
---

# size(forChildContentContainer:withParentContainerSize:)

Returns the size of the specified child view controller’s content.

## Declaration

```swift
func size(forChildContentContainer container: any UIContentContainer, withParentContainerSize parentSize: CGSize) -> CGSize
```

## Parameters

- `container`: The child view controller.
- `parentSize`: The size of the parent view controller.

## Return Value

Return Value The size to apply to the child view controller.

## Discussion

Discussion Container view controllers use this method to return the sizes for their child view controllers. UIKit calls the method as part of the default implementation of the viewWillTransition(to:with:) method for view controllers. It calls the method once for each child view controller embedded in the view controller. If you’re implementing a custom container view controller, you should override this method and use it to return the sizes of the contained children. View controllers and presentation controllers return the value in parentSize by default.

## See Also

### Responding to changes in child view controllers

- [preferredContentSizeDidChange(forChildContentContainer:)](uikit/uicontentcontainer/preferredcontentsizedidchange(forchildcontentcontainer:).md)
- [systemLayoutFittingSizeDidChange(forChildContentContainer:)](uikit/uicontentcontainer/systemlayoutfittingsizedidchange(forchildcontentcontainer:).md)
- [preferredContentSize](uikit/uicontentcontainer/preferredcontentsize.md)