JavaScript : Never returns from await

Question

我正在尝试使用async/await，但await没有返回。

这是带有await的异步函数。

async _checkEmailDuplication() {
    try {
        console.log('Check Email Duplication is called');
        let res = await MyNetwork.checkEmail(this.state.email);
        console.log('Check email return value: ' + res);
        if (res === 0) {
            console.log('Available Email');
            return false;
        }
        else {
            console.log('Email Duplication Check Error');
            return true;
        }
    }
    catch (e) {
        console.error('Check Email Call Error', e.message);
        return true;
    }
    console.log('What happened?');
    return true;
}

正在调用checkEmail函数，这里是检查Email函数定义

export type EmailCheckResponse = { ret?: number };

class Network {
    constructor() {
        this._network = NativeModules.NetworkService;
    }
    checkEmail = (email: string): Promise<EmailCheckResponse> => {
        console.log('Network CheckEmail is called');
        return this._network.checkEmail(email);
    }
}

这是react-native模块并尝试使用iOS中的Nativemodules。

这是 Objective-C Native 模块导出部分。

RCT_EXPORT_METHOD(checkEmail:(NSString *)email 
    resolver:(RCTPromiseResolveBlock)resolve 
    rejecter:(RCTPromiseRejectBlock)reject)
{
    @autoreleasepool {
        [GRPCCall useInsecureConnectionsForHost:kHostAddress];

        AccountService *client = [[AccountService alloc] initWithHost:kHostAddress];

        EmailCheckRequest *request = [EmailCheckRequest message];
        request.email = email;
        NSLog(@"Requested Email: %@\n", request.email);

        [client checkEmailWithRequest:request handler:^(EmailCheckResponse *response, NSError *error) {
        NSLog(@"Email Check result: %d\n", response.ret);
        }];
    }
}

问题是调用checkEmail后，卡住了。没有返回。

日志说

2017-07-16 16:01:29.355 [info][tid:com.facebook.React.JavaScript] 检查电子邮件重复被调用2017-07-16 16:01:29.356 [info][tid:com.facebook.React.JavaScript] 网络 CheckEmail 被调用2017-07-16 16:01:29.364 [50446:3725293] 请求的电子邮件:xxx@xxx.com2017-07-16 16:01:29.384 [50446:3725170] 电子邮件检查结果:0

看来 Objective-C 模块已成功调用，但没有返回。调用await checkEmail后，没有任何反应。

有人可以告诉我的代码有什么问题吗？ =(

Answer 1

我可以从你的React native 模块实现中看到，你忘记调用resolve和reject方法，这对于工作 promise 的工作方式至关重要。

[client checkEmailWithRequest:request handler:^(EmailCheckResponse *response, NSError *error) {
    NSLog(@"Email Check result: %d\n", response.ret);
        if(response){
           resolve(response);
       }else{
           reject(@"no_events", @"There were no events", error);
       }
 }
];

希望这对您有帮助。