Storing MutableMap on SharedPreferences and retrieving it

August 29, 2022

I was trying to store a MutableMap in shared preferences so I could retrieve it later, but my app is crashing when retrieving and casting the mutableMap.

First I initialized the map and filled it with values

val mapYearMonths: MutableMap<Int, Map<Int, Map<Int, Map<Map<String, Int>, Int>>>> =
                HashMap<Int, Map<Int, Map<Int, Map<Map<String, Int>, Int>>>>()

Then I stored it, which seems to work correctly:

 val stepsRecord: String = Gson().toJson(mapYearMonths)
        val editor = sharedPreferences.edit();
        editor.putString("stepsRecord", stepsRecord);
        editor.commit();

And finally I retrieved it, which crashes at line 3

val mapYearMonthsString: String = sharedPreferences.getString("stepsRecord", "0")!!
        val mapYearMonthsAny: MutableMap<*, *>? =
            Gson().fromJson(mapYearMonthsString, MutableMap::class.java)
        return mapYearMonthsAny as MutableMap<Int, Map<Int, Map<Int, Map<Map<String, Int>, Int>>>>

This is the error I get:

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.walker/com.example.walker.MainActivity}: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was NUMBER at line 1 column 2 path $
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3308)

Any clue on what I could be doing wrong? I tried looking up but couldn’t find anything on this. What am I doing something wrong? Should I use another method to store the data? Thanks everyone for the help in advance!

>Solution :

"0" is not a JSON object and cannot be parsed as a MutableMap. Use a default value that can be parsed as a MutableMap, such as "{}" for an empty map.