如何从方法内部的响应中获取结果？

Question

我是新 android 开发人员，我如何从这个片段中获得结果，存在什么方法，因为它 return 什么都没有，因为我在 onResponse 中添加元素，但仅使用 kotlin 模块：

private fun foo(list: ArrayList<CurrencyModel> = ArrayList()): ArrayList<CurrencyModel> {

        val request = Request.Builder().url(BASE_URL_YESTERDAY).build()

        val client = OkHttpClient()
        client.newCall(request).enqueue(object : Callback {

            override fun onFailure(call: Call, e: IOException) {

            }

            override fun onResponse(call: Call, response: Response) {
                val body = response.body?.string()
                val data = Gson().fromJson(body, Currencies::class.java)
                list.add(CurrencyModel("USD", data.rates.USD, 0.0))
                list.add(CurrencyModel("SEK", data.rates.SEK, 0.0))
                list.add(CurrencyModel("EUR", data.rates.EUR, 0.0))
            }
        })
        return list
    }
}

Answer 1

onResponse() function is only called when the HTTP response is successfully returned by the remote server. Since this response doesn't happen immediately, you can't use the result in your code immediately. What you could do is use a ViewModel and LiveData 变量并将值添加到 onResponse() 中的该变量。类似于：

private fun foo(list: ArrayList<CurrencyModel> = ArrayList()) {

val request = Request.Builder().url(BASE_URL_YESTERDAY).build()

val client = OkHttpClient()
client.newCall(request).enqueue(object : Callback {

    override fun onFailure(call: Call, e: IOException) {

    }

    override fun onResponse(call: Call, response: Response) {
        val body = response.body?.string()
        val data = Gson().fromJson(body, Currencies::class.java)
        val list: ArrayList<CurrencyModel> = arrayListOf()
        list.add(CurrencyModel("USD", data.rates.USD, 0.0))
        list.add(CurrencyModel("SEK", data.rates.SEK, 0.0))
        list.add(CurrencyModel("EUR", data.rates.EUR, 0.0))
        viewModel.list.postValue(list)
    }
})

}

Answer 2

您可以为您的函数提供一个回调参数，该参数会在收到响应时调用。在这种情况下你不应该有一个输入列表，因为如果你有多个源在不可预测的未来时刻修改它，它将很难跟踪。

函数可以如下所示：

private fun getCurrencyModels(callback: (ArrayList<CurrencyModel>) {

    val request = Request.Builder().url(BASE_URL_YESTERDAY).build()

    val client = OkHttpClient()
    client.newCall(request).enqueue(object : Callback {

        override fun onFailure(call: Call, e: IOException) {

        }

        override fun onResponse(call: Call, response: Response) {
            val body = response.body?.string()
            val data = Gson().fromJson(body, Currencies::class.java)
            val list = arrayListOf(
                CurrencyModel("USD", data.rates.USD, 0.0)),
                CurrencyModel("SEK", data.rates.SEK, 0.0)),
                CurrencyModel("EUR", data.rates.EUR, 0.0))
            )
            callback(list)
        }
    })
}

然后使用它：

getCurrencyModels { modelsList ->
    // do something with modelsList when it arrives
}

另一种方法是使用协程，它允许您在没有回调的情况下执行异步操作。有人已经创建了一个库，可以让你在协程中使用 OkHttp 请求 here。您可以像这样将函数编写为挂起函数：

private suspend fun getCurrencyModels(): ArrayList<CurrencyModel> {

    val request = Request.Builder().url(BASE_URL_YESTERDAY).build()
    val client = OkHttpClient()
    val response = client.newCall(request).await()
    val body = response.body?.string()
    val data = Gson().fromJson(body, Currencies::class.java)
    return arrayListOf(
        CurrencyModel("USD", data.rates.USD, 0.0)),
        CurrencyModel("SEK", data.rates.SEK, 0.0)),
        CurrencyModel("EUR", data.rates.EUR, 0.0))
    )
}

然后像这样使用它：

lifecycleScope.launch {
    try {
        val currencyModels = getCurrencyModels()
        // do something with currencyModels
    } catch (e: IOException) {
        // request failed
    }
}

当您的异步调用比您的 Activity 或 Fragment 寿命更长时，协程可以很容易地避免内存泄漏。在这种情况下，如果您的 Activity 在请求进行时关闭，它将自动取消并且对您的 Activity 的引用将被删除，以便垃圾收集器可以释放您的 Activity.

如何从方法内部的响应中获取结果？

How to get result from response inside method?

android

gson

kotlin