UIViewとしてFlutter Widgetを表示するView

FlutterView.swift

import UIKit
import Flutter

@IBDesignable
class FlutterView: UIView {

  @IBInspectable
  var routeName: String = "" {
    didSet {
      setupFlutterView()
    }
  }

  private var flutterView: UIView? = nil

  override func layoutSubviews() {
    super.layoutSubviews()
    setupFlutterView()
  }

  private func setupFlutterView() {
    flutterView?.removeFromSuperview()
    let flutterViewController = FlutterViewController(
      project: nil,
      initialRoute: routeName,
      nibName: nil,
      bundle: nil
    )
    flutterViewController.view.translatesAutoresizingMaskIntoConstraints = false
    guard let flutterView = flutterViewController.view else {
      return
    }
    self.flutterView = flutterView
    addSubview(flutterView)
    NSLayoutConstraint.activate([
      flutterView.topAnchor.constraint(equalTo: topAnchor),
      flutterView.bottomAnchor.constraint(equalTo: bottomAnchor),
      flutterView.leadingAnchor.constraint(equalTo: leadingAnchor),
      flutterView.trailingAnchor.constraint(equalTo: trailingAnchor),
    ])
    flutterView.layoutIfNeeded()
  }
}

routeName には FlutterのMaterial Appで設定している、route path を入れてください。

widgetで切ると良さそう
/widget/hoge_widget