Cómo mostrar una ventana de información para un marcador

import GoogleMaps
import UIKit

final class MarkerInfoWindowViewController: UIViewController {

  private let sydneyMarker = GMSMarker(
    position: CLLocationCoordinate2D(latitude: -33.8683, longitude: 151.2086))

  private let melbourneMarker = GMSMarker(
    position: CLLocationCoordinate2D(latitude: -37.81969, longitude: 144.966085))

  private let brisbaneMarker = GMSMarker(
    position: CLLocationCoordinate2D(latitude: -27.4710107, longitude: 153.0234489))

  private lazy var contentView: UIImageView = {
    return UIImageView(image: UIImage(named: "aeroplane"))
  }()

  override func loadView() {
    let cameraPosition = GMSCameraPosition(latitude: -37.81969, longitude: 144.966085, zoom: 4)
    let mapView = GMSMapView(frame: .zero, camera: cameraPosition)
    mapView.delegate = self
    view = mapView

    sydneyMarker.title = "Sydney"
    sydneyMarker.snippet = "Population: 4,605,992"
    sydneyMarker.map = mapView

    melbourneMarker.title = "Melbourne"
    melbourneMarker.snippet = "Population: 4,169,103"
    melbourneMarker.map = mapView

    brisbaneMarker.title = "Brisbane"
    brisbaneMarker.snippet = "Population: 2,189,878"
    brisbaneMarker.map = mapView
  }
}

extension MarkerInfoWindowViewController: GMSMapViewDelegate {
  func mapView(_ mapView: GMSMapView, markerInfoWindow marker: GMSMarker) -> UIView? {
    if marker == sydneyMarker {
      return contentView
    }
    return nil
  }

  func mapView(_ mapView: GMSMapView, markerInfoContents marker: GMSMarker) -> UIView? {
    if marker == brisbaneMarker {
      return contentView
    }
    return nil
  }

  func mapView(_ mapView: GMSMapView, didCloseInfoWindowOf marker: GMSMarker) {
    showToast(message: "Info window for marker \(marker.title ?? "") closed.")
  }

  func mapView(_ mapView: GMSMapView, didLongPressInfoWindowOf marker: GMSMarker) {
    showToast(message: "Info window for marker \(marker.title ?? "") long pressed.")
  }
}

extension UIViewController {
  func showToast(message: String) {
    let toast = UIAlertController(title: nil, message: message, preferredStyle: .alert)
    present(
      toast, animated: true,
      completion: {
        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + .seconds(2)) {
          toast.dismiss(animated: true)
        }
      })
  }
}
MarkerInfoWindowViewController.swift
      

#import "GoogleMapsDemos/Samples/MarkerInfoWindowViewController.h"

#import "GoogleMapsDemos/UIViewController+GMSToastMessages.h"
#import <GoogleMaps/GoogleMaps.h>

@interface MarkerInfoWindowViewController () <GMSMapViewDelegate>

@end

@implementation MarkerInfoWindowViewController {
  GMSMarker *_sydneyMarker;
  GMSMarker *_melbourneMarker;
  GMSMarker *_brisbaneMarker;
  UIView *_contentView;
}

- (void)viewDidLoad {
  [super viewDidLoad];
  GMSCameraPosition *camera = [GMSCameraPosition cameraWithLatitude:-37.81969
                                                          longitude:144.966085
                                                               zoom:4];
  GMSMapView *mapView = [GMSMapView mapWithFrame:CGRectZero camera:camera];

  _sydneyMarker = [[GMSMarker alloc] init];
  _sydneyMarker.title = @"Sydney";
  _sydneyMarker.snippet = @"Population: 4,605,992";
  _sydneyMarker.position = CLLocationCoordinate2DMake(-33.8683, 151.2086);
  _sydneyMarker.map = mapView;
  NSLog(@"sydneyMarker: %@", _sydneyMarker);

  _melbourneMarker.map = nil;
  _melbourneMarker = [[GMSMarker alloc] init];
  _melbourneMarker.title = @"Melbourne";
  _melbourneMarker.snippet = @"Population: 4,169,103";
  _melbourneMarker.position = CLLocationCoordinate2DMake(-37.81969, 144.966085);
  _melbourneMarker.map = mapView;
  NSLog(@"melbourneMarker: %@", _melbourneMarker);

  _brisbaneMarker.map = nil;
  _brisbaneMarker = [[GMSMarker alloc] init];
  _brisbaneMarker.title = @"Brisbane";
  _brisbaneMarker.snippet = @"Population: 2,189,878";
  _brisbaneMarker.position = CLLocationCoordinate2DMake(-27.4710107, 153.0234489);
  _brisbaneMarker.map = mapView;
  NSLog(@"brisbaneMarker: %@", _brisbaneMarker);

  _contentView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"aeroplane"]];

  mapView.delegate = self;
  self.view = mapView;
}

#pragma mark GMSMapViewDelegate

- (UIView *)mapView:(GMSMapView *)mapView markerInfoWindow:(GMSMarker *)marker {
  if (marker == _sydneyMarker) {
    return _contentView;
  }
  return nil;
}

- (UIView *)mapView:(GMSMapView *)mapView markerInfoContents:(GMSMarker *)marker {
  if (marker == _brisbaneMarker) {
    return _contentView;
  }
  return nil;
}

- (void)mapView:(GMSMapView *)mapView didCloseInfoWindowOfMarker:(GMSMarker *)marker {
  NSString *message =
      [NSString stringWithFormat:@"Info window for marker %@ closed.", marker.title];
  [self gms_showToastWithMessage:message];
}

- (void)mapView:(GMSMapView *)mapView didLongPressInfoWindowOfMarker:(GMSMarker *)marker {
  NSString *message =
      [NSString stringWithFormat:@"Info window for marker %@ long pressed.", marker.title];
  [self gms_showToastWithMessage:message];
}

@end
MarkerInfoWindowViewController.m