Answer: layoutSubviews is called by the system whenever a view's bounds change or its subview layout needs to be recalculated. Override it for manual layout.

Code Example:

class CustomView: UIView {

    override func layoutSubviews() {
        super.layoutSubviews()  // always call super first

        // Manual frame-based layout using self.bounds
        let padding: CGFloat = 16
        avatarImageView.frame = CGRect(x: padding, y: padding,
                                       width: 44, height: 44)
        nameLabel.frame = CGRect(x: avatarImageView.frame.maxX + 8,
                                  y: padding,
                                  width: bounds.width - 72,
                                  height: 44)
    }
}

// Trigger layout
view.setNeedsLayout()     // marks as dirty, updates on next render cycle
view.layoutIfNeeded()     // forces immediate layout (e.g. before animation)

When it's called: bounds change, setNeedsLayout, adding/removing subviews, device rotation.