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等待来自Kotlin中多个回调/lambda的结果

okhttp kotlin asynchronous

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BillyDean · 技术社区 · 6 年前

我在科特林做一个应用程序。直到现在,我的网络电话还不需要一起使用。现在我需要进行两个并发的网络调用,暂停直到我收到它们的两个响应,然后继续执行。我正努力完成这样的事情:

    //first networking call, get resourceOne
    var resourceOne : String?
    Server.asyncRequest(RequestBuilder(endpoints.second, ids, params)) { resource: String?, error: ServiceError? ->
        resourceOne = resource
    }

    //second networking call, get resourceTwo
    var resourceTwo : String?
    Server.asyncRequest(RequestBuilder(endpoints.third, ids, params)) { resource: String?, error: ServiceError? ->
        resourceTwo = resource
    }

    //do something here wiith resourceOne and resourceTwo

asyncRequest函数的函数头是:

fun asyncRequest(requestBuilder: RequestBuilder, completion: (resource: String?, error: ServiceError?) -> Unit) {

它只是包装一个okhttp请求,并进行一些额外的处理/解析。通常,我只需要获取结果(资源)并在完成lambda内处理它,但是由于我需要两个值,所以不能在这里这样做。我试过做类似的事情 this 但是我的asyncRequest函数没有返回类型,所以我无法像link那样执行async/await。

0 回复 | 直到 6 年前

1

3

Glenn Sandoval 6 年前

你可以用它 协同程序 像这样:

转弯回拨 可悬函数 suspendCancellableCoroutine {...} 阻止:

suspend fun <T> request(requestBuilder: RequestBuilder): T = suspendCancellableCoroutine { cont ->
    Server.asyncRequest(requestBuilder) { resource: T, error: ServiceError? ->
        if(error != null)
            cont.resumeWithException(error) // Makes the Flow throw an exception
        else
            cont.resume(resource) // Makes the Flow emit a correct result
    }
}

创建流量使 :

val resourceOneFlow = flow {
    emit(request<String>(RequestBuilder(endpoints.second, ids, params)))
}

创建使 :

val resourceTwoFlow = flow {
    emit(request<String>(RequestBuilder(endpoints.third, ids, params)))
}

联合收割机 二者都流量和 zip

val requestsResultFlow = resourceOneFlow.zip(resourceTwoFlow) { resourceOne, resourceTwo ->
    // Build whatever you need with resourceOne and resourceTwo here and let it flow
    "$resourceOne $resourceTwo".length // Here I concatenate both strings and return its length
}

流量和 collect 运算符并使用其结果

requestsResultFlow.collect { length ->
    // Consume the result here
    println("$length") // Here I print the number received
}

你有 here .