Android Kotlin - save and retrieve JSONArray in SharedPreferences using gson or what ever

I've already wasted many hours on this.

I need to store and retrieve val response = JSONArray(it) in SharedPreferences.

So far I've only tried it with GSON

Attempt 1:

prefs.edit().putString("amz", response.toString()).apply()
val jsonPref = prefs.getString("amz", "")
val jArr: JsonArray = Gson().fromJson(jsonPref, JsonArray::class.java)
val title = jArr.getJSONObject(0).getString("title")

I get unresolved reference on getJSONObject even though it would work doing:

val title = response.getJSONObject(0).getString("title")

response and jArr look different.

response:

[{"asin":"B0015Z9KS2","title":"Eierbecher mit Stil ^^ 🐔🥚🐔","picurl":"\/amzimg\/B0015Z9KS2.jpg"},{"asin":"B002SQG4TU","title":"S**t happens... 😋😍😁","picurl":"\/amzimg\/B002SQG4TU.jpg"}]

jArr:

[{"asin":"B0015Z9KS2","title":"Eierbecher mit Stil ^^ 🐔🥚🐔","picurl":"/amzimg/B0015Z9KS2.jpg"},{"asin":"B002SQG4TU","title":"S**t happens... 😋😍😁","picurl":"/amzimg/B002SQG4TU.jpg"}]

So response is escaped, jArr not

Attempt 2:

prefs.edit().putString("amz", response.toString()).apply()
val jsonPref = prefs.getString("amz", "")
val jArr: JsonArray = JsonParser.parseString(jsonPref).asJsonArray
val title = jArr.getJSONObject(0).getString("title")

exactly the same issue as in attempt 1.

Attempt 3:

prefs.edit().putString("amz", Gson().toJson(response)).apply()
val jsonPref = prefs.getString("amz", "")
val jArr: JsonArray = Gson().fromJson(jsonPref, JsonArray::class.java)

Here I get

Expected a com.google.gson.JsonArray but was com.google.gson.JsonObject

on

val jArr: JsonArray = Gson().fromJson(jsonPref, JsonArray::class.java)

Attempt 4:

prefs.edit().putString("amz", Gson().toJson(response)).apply()
val jsonPref = prefs.getString("amz", "")
val jArr: JSONArray = Gson().fromJson(jsonPref, JSONArray::class.java)

note the difference between JsonArray and JSONArray

and here I get this stupid nonsense when printing jArr:

["{nameValuePairs={asin=B0015Z9KS2, title=Eierbecher mit Stil ^^ 🐔🥚🐔, picurl=\/amzimg\/B0015Z9KS2.jpg}}","{nameValuePairs={asin=B002SQG4TU, title=S**t happens... 😋😍😁, picurl=\/amzimg\/B002SQG4TU.jpg}}"]

Please help!

The main problem here seems to be that you are mixing multiple JSON libraries. JSONArray might be from JSON-java whereas your other code is using Gson. That also explains the issues you encountered:

> I get unresolved reference on getJSONObject even though it would work doing:
>
> kotlin
> val title = response.getJSONObject(0).getString("title")
>

jArr.getJSONObject(0) won't work because Gson has a completely different API (your IDE should suggest you the existing functions). The Gson equivalent is probably jArr.get(0).getAsJsonObject().

> response and jArr look different

This should not matter. The only difference seems to be that / is escaped, and that is optional (see also the JSON specification). It does not change the meaning of the represented data, and to any compliant JSON library it should not matter whether / or \/ appears in the JSON data.

> kotlin
> prefs.edit().putString("amz", Gson().toJson(response)).apply()
> ...
>
> Here I get
>
> Expected a com.google.gson.JsonArray but was com.google.gson.JsonObject
>

This is most likely 'expected'. response has the type JSONArray which is unknown to Gson because it comes from a different JSON library. Therefore it treats it as regular class without built-in adapter and uses reflection to serialize it. This leads to a JSON object containing all the internal fields of the JSONArray class instead of it being serialized as JSON array. Therefore when you try to deserialize it again it fails because it was serialized as JSON object not as JSON array.

As side note: In general you should avoid relying on Gson's reflection-based serialization for third-party classes because you then depend on their implementation details which could change at any point.

> note the difference between JsonArray and JSONArray
> and here I get this stupid nonsense when printing jArr:

Similar to the previous one, except that you are now also deserializing it.

So in summary: Don't mix different JSON libraries. Either stick to JSON-java or to Gson, but not both. If really necessary you can use them in different parts of your code as long as you only exchange JSON data between them, but be careful with exchanging library-specific objects.