flutter - 不要跨异步间隙使用 BuildContexts flutter

Question

我已经创建了一个注册函数，但在 Utils.flushBarErrorMessage("No Internet", context);Do not use BuildContexts across async gaps. 上收到警告 我是 Flutter 的新手，想知道如何使用 async 和 await。

Future _registration() async {
    String name = _nameController.text.trim();
    String email = _emailController.text.trim();
    String password = _passwordController.text.trim();
    String phone = _phoneController.text.trim();

    if (name.isEmpty) {
      Utils.flushBarErrorMessage("Type your name", context);
    } else if (email.isEmpty) {
      Utils.flushBarErrorMessage("Type your email", context);
    } else if (!GetUtils.isEmail(email)) {
      Utils.flushBarErrorMessage("Type valid email address", context);
    } else if (password.isEmpty) {
      Utils.flushBarErrorMessage("Type your password", context);
    } else if (password.length < 6) {
      Utils.flushBarErrorMessage(
          "password can't be less than 6 characters", context);
    } else if (phone.isEmpty) {
      Utils.flushBarErrorMessage("Type your phone", context);
    }
    else {
      var connectivityResult = await (Connectivity().checkConnectivity());
      if (connectivityResult == ConnectivityResult.mobile ||
          connectivityResult == ConnectivityResult.wifi) {
        ApiCall.signUp(name, email, password, phone).then((value) {
          if (value.statusCode == 200) {
            if (json.decode(value.body)['success'] != null) {
              if (json.decode(value.body)["success"]) {
                RegisterResponse registerResponseModel =
                    RegisterResponse.fromJson(json.decode(value.body));
                Navigator.pushNamed(context, VerifyUser.routeName);
                Utils.flushBarErrorMessage(
                    'User Registered Successfully', context);
                if (kDebugMode) {
                  print('User Registered Successfully');
                }
              } else {
                Utils.flushBarErrorMessage(
                    json.decode(value.body)["en_message"], context);
                if (kDebugMode) {
                  print(json.decode(value.body).toString());
                }
              }
            }
          } else {
            Utils.flushBarErrorMessage('invalid data', context);
            if (kDebugMode) {
              print(json.decode(value.body).toString());
            }
          }
        });
      } else {
        Utils.flushBarErrorMessage("No Internet", context);
      }
    }
  }

调用此 _registration()

ElevatedButton(
            onPressed: () {
              _registration();
            },
            child: const Text('SignUp')),

这是我的flushBarErrorMessage。

   class Utils {
  static void flushBarErrorMessage(String message, BuildContext context) {
    showFlushbar(
        context: context,
        flushbar: Flushbar(
          forwardAnimationCurve: Curves.decelerate,
          margin: const EdgeInsets.symmetric(horizontal: 20, vertical: 10),
          padding: const EdgeInsets.all(15),
          titleColor: Colors.white,
          duration: const Duration(seconds: 3),
          borderRadius: BorderRadius.circular(10),
          reverseAnimationCurve: Curves.easeInOut,
          icon: const Icon(
            Icons.error,
            size: 28,
            color: Colors.white,
          ),
          flushbarPosition: FlushbarPosition.TOP,
          positionOffset: 20,
          message: message,
          backgroundColor: Colors.red,
        )..show(context));
  }
}

Answer 1

问题是在 await 之后，每次使用 BuildContext 都会显示此警告。出现此警告是因为在处理小部件后可能会在 await 之后使用 BuildContext。这样，上下文将不再存在，应用程序甚至可能因此崩溃。查看the official lint documentation :

Storing BuildContext for later usage can easily lead to difficult-to-diagnose crashes. Asynchronous gaps are implicitly storing BuildContext and are some of the easiest to overlook when writing code.

来自官方文档的简单解决方案是需要检查 State.mounted .在出现警告的每个地方，代码看起来都像这样:

      ...
      } else {
        if (mounted) Utils.flushBarErrorMessage("No Internet", context);
      }
      ...