Optimize Google mobile ad initialization and loading on Flutter

One way of doing this is with the variable isBannerLoaded along with the BannerAdListener.

import 'dart:developer';

import 'package:flutter/material.dart';
import 'package:google_mobile_ads/google_mobile_ads.dart';
import 'package:provider/provider.dart';

class AdBanner extends StatefulWidget {
  final String adUnitId;
  final AdSize size;
  const AdBanner({this.adUnitId, this.size});

  @override
  State<AdBanner> createState() => _AdBannerState();

  static AdSize getBannerSize() {
    final width =
        MediaQueryData.fromWindow(WidgetsBinding.instance.window).size.width;
    final height =
        MediaQueryData.fromWindow(WidgetsBinding.instance.window).size.height;
    if ((width >= 460 && width <= 500) || (height >= 800 && height <= 900)) {
      return AdSize(width: 336, height: 280);
    } else if ((width >= 360 && width <= 375) ||
        (height >= 600 && height <= 700)) {
      return AdSize(width: 320, height: 100);
    } else if ((width >= 375 && width <= 414) ||
        (height >= 700 && height <= 800)) {
      return AdSize(width: 300, height: 250);
    } else if ((width >= 300 && width <= 360) ||
        (height >= 400 && height <= 600)) {
      return AdSize(width: 320, height: 50);
    } else {
      return AdSize(width: 320, height: 50);
    }
  }
}

class _AdBannerState extends State<AdBanner> {
  bool isBannerLoaded = false;
  BannerAd myBanner;
  @override
  Widget build(BuildContext context) {
    print('AdBanner build : ' + widget.adUnitId);
   
    final BannerAd bannerAd = myBanner;
    if (isBannerLoaded && bannerAd != null) {
      return Container(
          height: bannerAd.size.height.toDouble(),
          width: bannerAd.size.width.toDouble(),
          child: AdWidget(ad: bannerAd));
    } else {
      return Container(
      );
    }

   
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    myBanner = BannerAd(
      adUnitId: widget.adUnitId ?? '/234721286/NY_KB_Home_Micrec_23',
      size: widget.size ?? AdSize.banner,
      request: AdRequest(),
      listener: BannerAdListener(
        onAdLoaded: (Ad ad) {
          print('AdBanner onAdLoaded : ' + ad.adUnitId);
          setState(() {
            isBannerLoaded = true;
          });
        },
        // Called when an ad request failed.
        onAdFailedToLoad: (Ad ad, LoadAdError error) {
          print('inside failed');
          // Dispose the ad here to free resources.
          ad.dispose();
          print('failed to load: $error');
        },
        // Called when an ad opens an overlay that covers the screen.
        onAdOpened: (Ad ad) => print('Ad opened.'),
        // Called when an ad removes an overlay that covers the screen.
        onAdClosed: (Ad ad) => print('Ad closed.'),
        // Called when an impression occurs on the ad.
        onAdImpression: (Ad ad) => print('Ad impression.'),
      ),
    )..load();
  }

  @override
  void dispose() {
    super.dispose();
    myBanner.dispose();
  }
}