The preferencesdelegate from timfreiheit

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Serializing a list of POJO objects with json

Hello to the project owner!

Seems like an interesting project.
Small question to see if it can solve neatly something that has bothered me recently.

I was recently trying to serialize with json & sharedpreferences a list of plain old java objects.
Let's say

data class Pojo (var foo : Int = 1, var bar : Int = 42)

It proved to be much combersome than necessary, because of type erasure on collection. See stackoverflow http://stackoverflow.com/questions/5813434/trouble-with-gson-serializing-an-arraylist-of-pojos

I ended up doing this (with this magical "type" variable telling gson that type information that was erased at compile time

public class PojoList (var list: List<Pojo> = emptyList()) {
    val KEY_POJOS = "PojoList"
    val type = object : TypeToken<ArrayList<Pojo>>() {}

    fun fetchFromDisk(context : Context) : Boolean {
        val preferences = context.getSharedPreferences("preferences.txt", Context.MODE_PRIVATE)

        val pojos = preferences.getString(KEY_POJOS, "")
        try {
            list = Gson().fromJson(pojos, type.getType())
            return true
        } catch(e: Exception) {
            return false
        }

    }
    fun saveToDisk(context: Context, list :  List<Pojo> ) {
        $list = list
        val preferences = context.getSharedPreferences("preferences.txt", Context.MODE_PRIVATE)
        preferences.edit()
                .putString(KEY_POJOS, Gson().toJson(list.toArrayList(), type.getType()))
                .apply()
    }

}