exemplo_admob_flutter_main_widget.dart

@override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: <Widget>[
            Container(
              child: getBanner(AdmobBannerSize.BANNER),
            ),
            Container(child: getBanner(AdmobBannerSize.MEDIUM_RECTANGLE)),
            Container(
              margin: const EdgeInsets.only(left: 20, right: 20),
              child: RaisedButton(
                  color: Colors.red,
                  child: Text(
                    "Exibir Interstitial!",
                    style: TextStyle(color: Colors.white),
                  ),
                  onPressed: () {
                    showInterstitial();
                  }),
            )
          ],
        ));
  }

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