Add game_template (#1180)

Adds a template / sample for games built in Flutter, with all the bells and whistles, like ads, in-app purchases, audio, main menu, settings, and so on.

Co-authored-by: Parker Lougheed
Co-authored-by: Shams Zakhour

game_template/lib/src/ads/ads_controller.dart

@@ -0,0 +1,62 @@
+// Copyright 2022, the Flutter project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:google_mobile_ads/google_mobile_ads.dart';
+
+import 'preloaded_banner_ad.dart';
+
+/// Allows showing ads. A facade for `package:google_mobile_ads`.
+class AdsController {
+  final MobileAds _instance;
+
+  PreloadedBannerAd? _preloadedAd;
+
+  /// Creates an [AdsController] that wraps around a [MobileAds] [instance].
+  ///
+  /// Example usage:
+  ///
+  ///     var controller = AdsController(MobileAds.instance);
+  AdsController(MobileAds instance) : _instance = instance;
+
+  void dispose() {
+    _preloadedAd?.dispose();
+  }
+
+  /// Initializes the injected [MobileAds.instance].
+  Future<void> initialize() async {
+    await _instance.initialize();
+  }
+
+  /// Starts preloading an ad to be used later.
+  ///
+  /// The work doesn't start immediately so that calling this doesn't have
+  /// adverse effects (jank) during start of a new screen.
+  void preloadAd() {
+    // TODO: When ready, change this to the Ad Unit IDs provided by AdMob.
+    //       The current values are AdMob's sample IDs.
+    final adUnitId = defaultTargetPlatform == TargetPlatform.android
+        ? 'ca-app-pub-3940256099942544/6300978111'
+        // iOS
+        : 'ca-app-pub-3940256099942544/2934735716';
+    _preloadedAd =
+        PreloadedBannerAd(size: AdSize.mediumRectangle, adUnitId: adUnitId);
+
+    // Wait a bit so that calling at start of a new screen doesn't have
+    // adverse effects on performance.
+    Future<void>.delayed(const Duration(seconds: 1)).then((_) {
+      return _preloadedAd!.load();
+    });
+  }
+
+  /// Allows caller to take ownership of a [PreloadedBannerAd].
+  ///
+  /// If this method returns a non-null value, then the caller is responsible
+  /// for disposing of the loaded ad.
+  PreloadedBannerAd? takePreloadedAd() {
+    final ad = _preloadedAd;
+    _preloadedAd = null;
+    return ad;
+  }
+}