UIViewControllerRepresentableのレイアウト処理のサンプル

SampleViewController.swift

import UIKit
import SwiftUI

class SampleViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        let traits = [UITraitPreferredContentSizeCategory.self]
        registerForTraitChanges(traits) { (self: Self, _) in
            self.view.invalidateIntrinsicContentSize()
        }
    }
}

struct ViewControllerRepresentable<ViewController: UIViewController>: UIViewControllerRepresentable {
    func makeUIViewController(context: Context) -> ViewController {
        ViewController()
    }

    func updateUIViewController(_ uiViewController: ViewController, context: Context) {}

    func sizeThatFits(
        _ proposal: ProposedViewSize,
        uiViewController: ViewController,
        context: Context
    ) -> CGSize? {
        let size = CGSize(
            width: proposal.width ?? UIView.noIntrinsicMetric,
            height: proposal.height ?? UIView.noIntrinsicMetric
        )
        return uiViewController.view.systemLayoutSizeFitting(
            size,
            withHorizontalFittingPriority: .fittingSizeLevel,
            verticalFittingPriority: .defaultLow
        )
    }
}

#Preview {
    @Previewable @State var count = 0
    var dynamicTypeSize: DynamicTypeSize {
        let allCases = DynamicTypeSize.allCases
        return allCases[count % allCases.count]
    }
    ViewControllerRepresentable<SampleViewController>()
        .fixedSize()
        .padding()
        .background(Color.blue.secondary)
        .clipShape(.rect(cornerRadius: 10))
        .contentShape(.rect(cornerRadius: 10))
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(.background)
        .environment(\.dynamicTypeSize, dynamicTypeSize)
        .tint(.pink)
        .onTapGesture { count += 1 }
    Text(String(describing: dynamicTypeSize))
}

SampleViewController.xib

<?xml version="1.0" encoding="UTF-8"?>
<document type="com.apple.InterfaceBuilder3.CocoaTouch.XIB" version="3.0" toolsVersion="23502" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" useTraitCollections="YES" useSafeAreas="YES" colorMatched="YES">
    <device id="retina6_12" orientation="portrait" appearance="light"/>
    <dependencies>
        <plugIn identifier="com.apple.InterfaceBuilder.IBCocoaTouchPlugin" version="23504"/>
        <capability name="Image references" minToolsVersion="12.0"/>
        <capability name="Safe area layout guides" minToolsVersion="9.0"/>
        <capability name="System colors in document resources" minToolsVersion="11.0"/>
        <capability name="documents saved in the Xcode 8 format" minToolsVersion="8.0"/>
    </dependencies>
    <objects>
        <placeholder placeholderIdentifier="IBFilesOwner" id="-1" userLabel="File's Owner" customClass="SampleViewController" customModule="RepresentableSample" customModuleProvider="target">
            <connections>
                <outlet property="view" destination="i5M-Pr-FkT" id="sfx-zR-JGt"/>
            </connections>
        </placeholder>
        <placeholder placeholderIdentifier="IBFirstResponder" id="-2" customClass="UIResponder"/>
        <view clearsContextBeforeDrawing="NO" contentMode="scaleToFill" id="i5M-Pr-FkT">
            <rect key="frame" x="0.0" y="0.0" width="393" height="852"/>
            <autoresizingMask key="autoresizingMask" widthSizable="YES" heightSizable="YES"/>
            <subviews>
                <stackView opaque="NO" contentMode="scaleToFill" horizontalHuggingPriority="1000" horizontalCompressionResistancePriority="1000" alignment="center" translatesAutoresizingMaskIntoConstraints="NO" id="Jah-Wg-omT">
                    <rect key="frame" x="0.0" y="59" width="393" height="793"/>
                    <subviews>
                        <stackView opaque="NO" contentMode="scaleToFill" horizontalHuggingPriority="1000" horizontalCompressionResistancePriority="1000" axis="vertical" alignment="center" translatesAutoresizingMaskIntoConstraints="NO" id="9Ig-3r-V8f">
                            <rect key="frame" x="0.0" y="342.66666666666669" width="393" height="107.66666666666669"/>
                            <subviews>
                                <imageView clipsSubviews="YES" userInteractionEnabled="NO" contentMode="scaleAspectFit" horizontalHuggingPriority="251" verticalHuggingPriority="751" verticalCompressionResistancePriority="751" adjustsImageSizeForAccessibilityContentSizeCategory="YES" translatesAutoresizingMaskIntoConstraints="NO" id="kDE-ij-fsY">
                                    <rect key="frame" x="166.66666666666666" y="-0.66666666666666785" width="60" height="34.666666666666671"/>
                                    <imageReference key="image" image="rainbow" catalog="system" symbolScale="large" renderingMode="original"/>
                                    <preferredSymbolConfiguration key="preferredSymbolConfiguration" configurationType="font" scale="large" weight="black">
                                        <fontDescription key="fontDescription" style="UICTFontTextStyleTitle1"/>
                                    </preferredSymbolConfiguration>
                                </imageView>
                                <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="1000" verticalHuggingPriority="751" horizontalCompressionResistancePriority="1000" verticalCompressionResistancePriority="751" text="Hello, world!" textAlignment="center" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontForContentSizeCategory="YES" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="aKX-7S-WBY">
                                    <rect key="frame" x="107.66666666666667" y="33.333333333333314" width="177.66666666666663" height="40.666666666666657"/>
                                    <fontDescription key="fontDescription" style="UICTFontTextStyleTitle0"/>
                                    <nil key="textColor"/>
                                    <nil key="highlightedColor"/>
                                </label>
                                <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="1000" verticalHuggingPriority="751" horizontalCompressionResistancePriority="1000" verticalCompressionResistancePriority="751" text="Hello, world!" textAlignment="center" lineBreakMode="tailTruncation" baselineAdjustment="alignBaselines" adjustsFontForContentSizeCategory="YES" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="PFp-5d-qnS">
                                    <rect key="frame" x="123" y="74" width="147" height="33.666666666666657"/>
                                    <fontDescription key="fontDescription" style="UICTFontTextStyleTitle1"/>
                                    <color key="textColor" systemColor="tintColor"/>
                                    <nil key="highlightedColor"/>
                                </label>
                            </subviews>
                        </stackView>
                    </subviews>
                </stackView>
            </subviews>
            <viewLayoutGuide key="safeArea" id="fnl-2z-Ty3"/>
            <color key="backgroundColor" white="0.0" alpha="0.0" colorSpace="custom" customColorSpace="genericGamma22GrayColorSpace"/>
            <constraints>
                <constraint firstItem="fnl-2z-Ty3" firstAttribute="trailing" secondItem="Jah-Wg-omT" secondAttribute="trailing" id="93d-y5-W2L"/>
                <constraint firstItem="Jah-Wg-omT" firstAttribute="top" secondItem="fnl-2z-Ty3" secondAttribute="top" id="NCi-G3-oGf"/>
                <constraint firstAttribute="bottom" secondItem="Jah-Wg-omT" secondAttribute="bottom" id="QdY-Em-Ojt"/>
                <constraint firstItem="Jah-Wg-omT" firstAttribute="leading" secondItem="fnl-2z-Ty3" secondAttribute="leading" id="Rf3-Vz-UFm"/>
            </constraints>
            <point key="canvasLocation" x="27" y="20"/>
        </view>
    </objects>
    <resources>
        <image name="rainbow" catalog="system" width="128" height="71"/>
        <systemColor name="tintColor">
            <color red="0.0" green="0.47843137254901963" blue="1" alpha="1" colorSpace="custom" customColorSpace="sRGB"/>
        </systemColor>
    </resources>
</document>