Kotlin how to Map JSONArray to Type (Stream)

问题

I'm trying to map my JSONArray to a Array<String?>.

I'm doing it like this:

fun getTextResponse(responseJson: JSONObject): Array<String?>{
        val resultData = responseJson.getJSONArray("data")
                .getJSONObject(0)
                .getJSONArray("result")

        return resultData.map{ it.getString("label") }.toTypedArray()
}

But it is not typed as a JSONObject, is there any way I can force type it to JSONObject ?

回答1:

The problem is that resultData has a type of JSONArray, which is a JSON utility class that doesn't overrides Kotlin/Java Array interface and thus doesn't have a map function.

You have to retrieve each string by index and generate new array like this:

fun getTextResponse(responseJson: JSONObject): Array<String?> {
    val resultData = responseJson.getJSONArray("data")
            .getJSONObject(0)
            .getJSONArray("result")
    return Array<String?>(resultData.length()) { i -> resultData.getString(i) }
}

回答2:

What jackqack proposed in his answer is what you should do, I just want to add that since you want to return an Array<String?> you should also map exceptions to null. This will make your code more robust. The generic type argument can be inferred too, so it can be omitted.

fun getTextResponse(responseJson: JSONObject): Array<String?> {
    val resultData = responseJson.getJSONArray("data")
            .getJSONObject(0)
            .getJSONArray("result")

    return Array(resultData.length()) { i ->

        try {
            resultData.getString(i)
        } catch (e: JSONException){
            null
        }
    }
}

回答3:

The problem is that your resutData does not have a map function! See https://developer.android.com/reference/org/json/JSONArray.

What you can do instead is iterate over the JSONArray and add every entry to your new Array, like this:

fun getTextResponse(responseJson: JSONObject): Array<String?>{
    val resultData = responseJson.getJSONArray("data")
            .getJSONObject(0)
            .getJSONArray("result")

    val arrayList = ArrayList<String>()
    for (i in 0..resultData.length()) {
        arrayList.add(resultData[i].toString())
    }

    return arrayList.toArray(arrayOfNulls<String>(arrayList.size))
}

来源：https://stackoverflow.com/questions/54136316/kotlin-how-to-map-jsonarray-to-type-stream

标签

kotlin

functional-programming

stream