What is the role of the viewWillLayoutSubviews method in the iOS view lifecycle and when is it called?

The viewWillLayoutSubviews method is called in the UIViewController lifecycle before the system begins laying out (arranging) the subviews of the current view. This occurs each time the layout or size of the subviews needs to be updated, such as when the device orientation changes or the view's size changes.

The main role of viewWillLayoutSubviews is to give developers an opportunity to make changes to the layout or sizes of subviews before they are actually laid out. This is useful if you need to programmatically adjust the interface to new conditions.

Example usage:

override func viewWillLayoutSubviews() {
    super.viewWillLayoutSubviews()
    // Adjust the frame of subviews before layout
    mySubview.frame = CGRect(x: 10, y: 10, width: view.bounds.width - 20, height: 100)
}

Important: this method can be called multiple times, so heavy operations should not be performed here.