Flutter集成in_app_purchase包触发java.lang.NullPointerException求助

我在Flutter项目中集成in_app_purchase包（用于对接自有后端验证购买），但运行后出现java.lang.NullPointerException错误，控制台仅输出：

W/BillingLogger( 7906): Unable to log.
W/BillingLogger( 7906): java.lang.NullPointerException

相关代码如下：

class SubscriptionPage extends StatefulWidget {
  const SubscriptionPage({super.key});

  @override
  State<SubscriptionPage> createState() => _SubscriptionPageState();
}

class _SubscriptionPageState extends State<SubscriptionPage> {
  final InAppPurchase _inAppPurchase = InAppPurchase.instance;
  late StreamSubscription<List<PurchaseDetails>> _subscription;

  //Product Listing
  static const List<String> _productIds = [
    'com.....subscription'
  ];

  @override
  void initState() {
    final Stream<List<PurchaseDetails>> purchaseUpdated =
        _inAppPurchase.purchaseStream;
    _subscription =
        purchaseUpdated.listen((List<PurchaseDetails> purchaseDetailsList) {
      if (mounted) {
        _listenToPurchaseUpdated(purchaseDetailsList, context);
      }
    }, onDone: () {
      _subscription.cancel();
    }, onError: (Object error) {
      if (mounted) {
        showSnackBar(context, 'Something went wrong', Severity.error);
      }
    });
    super.initState();
  }

  Future<Subscription> getProducts() async {
    final bool isAvailable = await _inAppPurchase.isAvailable();
    if (!isAvailable) {
      return Subscription(
        isAvailable: isAvailable,
        products: [],
        notFoundIds: [],
      );
    }
    final ProductDetailsResponse productDetailResponse =
        await _inAppPurchase.queryProductDetails(_productIds.toSet());

    if (productDetailResponse.error != null) {
      throw Exception(productDetailResponse.error!.message);
    }
    return Subscription(
      isAvailable: isAvailable,
      products: productDetailResponse.productDetails,
      notFoundIds: productDetailResponse.notFoundIDs,
    );
  }

  @override
  void dispose() {
    _subscription.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    var media = MediaQuery.of(context).size;
    return Scaffold(
      appBar: const BasicAppBar(
        title: 'Subscription',
        isBack: true,
        level: '3',
      ),
      body: Column(
        children: [
          //.....
        ],
      ),
    );
  }

  _listenToPurchaseUpdated(
      List<PurchaseDetails> purchaseDetailsList, BuildContext context) async {
    for (final PurchaseDetails purchaseDetails in purchaseDetailsList) {
      if (purchaseDetails.status == PurchaseStatus.pending) {
        showSnackBar(
          context,
          'You are purchasing a subscription',
          Severity.success,
        );
      } else if (purchaseDetails.status == PurchaseStatus.error) {
        showSnackBar(
          context,
          'Your purchased failed!',
          Severity.error,
        );
      } else if (purchaseDetails.status == PurchaseStatus.purchased) {
        showSnackBar(
          context,
          'Your purchase is successfully',
          Severity.success,
        );
      }
    }
  }
}

排查与解决建议 #

• 强制指定Google Billing库版本
  in_app_purchase底层依赖Google Play Billing库，版本不匹配可能触发空指针。在android/app/build.gradle中明确指定兼容版本：

  dependencies {
      implementation 'com.android.billingclient:billing:6.1.0'
  }
  

• 调整初始化时机
  避免在initState中直接订阅流，先确认服务可用再初始化：

  @override
  void initState() {
    super.initState();
    _initPurchaseStream();
  }
  
  Future<void> _initPurchaseStream() async {
    final bool isAvailable = await _inAppPurchase.isAvailable();
    if (isAvailable && mounted) {
      final Stream<List<PurchaseDetails>> purchaseUpdated = _inAppPurchase.purchaseStream;
      _subscription = purchaseUpdated.listen(
        (List<PurchaseDetails> purchaseDetailsList) {
          _listenToPurchaseUpdated(purchaseDetailsList, context);
        },
        onDone: () {
          if (mounted) _subscription.cancel();
        },
        onError: (Object error) {
          if (mounted) showSnackBar(context, 'Something went wrong', Severity.error);
        },
      );
    }
  }
  

• 校验产品ID与空值处理
  确保_productIds与Google Play Console中配置的订阅ID完全一致；同时在购买监听逻辑中增加空值判断：

  void _listenToPurchaseUpdated(
      List<PurchaseDetails> purchaseDetailsList, BuildContext context) {
    for (final PurchaseDetails? purchaseDetails in purchaseDetailsList) {
      if (purchaseDetails == null) continue;
      // 后续状态判断逻辑
    }
  }
  

• 清理构建缓存
  执行以下命令清理缓存后重新构建项目：

  flutter clean
  flutter pub get
  cd android && ./gradlew clean && cd ..
  

内容的提问来源于stack exchange，提问作者user25770779