How to load data class that include MutableList from SharedPreference?

Question

I'm trying to use SharedPreference and error occur when i load data. I think the problem is that my data class include MutableList, but i don't know how to handle it.

private lateinit var albumData:MutableList<Album>

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    loadData()

    connectAdapter()

    btnAddAlbum.setOnClickListener {
        if(isStoragePermitted()) {
            openGallery()
        }
    }
}

fun saveData() {
    val sharedPreferences = getSharedPreferences("shared preferences", Context.MODE_PRIVATE)
    val editor = sharedPreferences.edit()
    val gson = GsonBuilder().create()
    val json = gson.toJson(albumData)
    editor.putString("Album data", json)
    editor.apply()
}

fun loadData() {
    val sharedPreferences = getSharedPreferences("shared preferences", Context.MODE_PRIVATE)
    val gson = GsonBuilder().create()
    val json = sharedPreferences.getString("Album data", null)
    var test = mutableListOf<Album>()
    if(json != null) {
        Log.d("Log_show", "data load 1")
        val type = object : TypeToken<MutableList<Album>>() {}.type
        Log.d("Log_show", "data load 2")
        albumData = gson.fromJson<MutableList<Album>>(json, type)
        Log.d("Log_show", "data load 3")
    }else{
        albumData =  mutableListOf()
    }
}

override fun onDestroy() {
    saveData()
    Log.d("Log_show", "shut down")
    super.onDestroy()
}

Above is part of my functions in main activity.

data class Album (
    var albumImages : MutableList<Uri>,
    var albumTitle : String,
    var pictureCount : Int
)

This is my data class "Album"

When i first open the app, it save data well and no error occur.
But when i close the app and open it again, the error occur in process of loading data
This is part of my log of "Log_show" and "data load 3" didn't appear

2020-11-04 23:12:33.418 15720-15720/kr.co.ddophi.autochangingwallpaper D/log: data load 1
2020-11-04 23:12:33.420 15720-15720/kr.co.ddophi.autochangingwallpaper D/log: data load 2

the full log is like this

2020-11-05 14:48:19.319 6956-6956/kr.co.ddophi.autochangingwallpaper D/Log_show: data load 1 2020-11-05 14:48:19.321 6956-6956/kr.co.ddophi.autochangingwallpaper D/Log_show: data load 2 2020-11-05 14:48:19.331 6956-6956/kr.co.ddophi.autochangingwallpaper D/AndroidRuntime: Shutting down VM 2020-11-05 14:48:19.336 6956-6956/kr.co.ddophi.autochangingwallpaper E/AndroidRuntime: FATAL EXCEPTION: main Process: kr.co.ddophi.autochangingwallpaper, PID: 6956 java.lang.RuntimeException: Unable to start activity ComponentInfo{kr.co.ddophi.autochangingwallpaper/kr.co.ddophi.autochangingwallpaper.MainActivity}: java.lang.RuntimeException: Failed to invoke private android.net.Uri() with no args at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2957) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6944) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374) Caused by: java.lang.RuntimeException: Failed to invoke private android.net.Uri() with no args at com.google.gson.internal.ConstructorConstructor$3.construct(ConstructorConstructor.java:113) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:212) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at com.google.gson.Gson.fromJson(Gson.java:927) at com.google.gson.Gson.fromJson(Gson.java:892) at com.google.gson.Gson.fromJson(Gson.java:841) at kr.co.ddophi.autochangingwallpaper.MainActivity.loadData(MainActivity.kt:174) at kr.co.ddophi.autochangingwallpaper.MainActivity.onCreate(MainActivity.kt:43) at android.app.Activity.performCreate(Activity.java:7183) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2910) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6944) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374) Caused by: java.lang.InstantiationException: Can't instantiate abstract class android.net.Uri at java.lang.reflect.Constructor.newInstance0(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:334) at com.google.gson.internal.ConstructorConstructor$3.construct(ConstructorConstructor.java:110) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:212) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131) at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222) at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82) at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61) at com.google.gson.Gson.fromJson(Gson.java:927) at com.google.gson.Gson.fromJson(Gson.java:892) at com.google.gson.Gson.fromJson(Gson.java:841) at kr.co.ddophi.autochangingwallpaper.MainActivity.loadData(MainActivity.kt:174) at kr.co.ddophi.autochangingwallpaper.MainActivity.onCreate(MainActivity.kt:43) at android.app.Activity.performCreate(Activity.java:7183) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1220) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2910) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) at android.os.Handler.dispatchMessage(Handler.java:105) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6944) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

Any help would be appreciated
Thank you

Please in general include code snippets as code blocks instead of including only screenshots. Additionally could you please include the exact exception message and stack trace please? — Marcono1234, Nov 04 '20 at 21:02
Similar to https://stackoverflow.com/q/46031104; Gson cannot create an instance of URI because it is an `abstract` class. You could either switch to `String` or write a [`TypeAdapter`](https://www.javadoc.io/doc/com.google.code.gson/gson/2.8.6/com.google.gson/com/google/gson/TypeAdapter.html) which uses `URI.toString()` and `URI.parse(...)`. I can provide an example, but only in Java (maybe it is helpful nonetheless). — Marcono1234, Nov 05 '20 at 13:59
Oh, that's nice idea. I'll try that method. Thank you very much! — Ddophi, Nov 06 '20 at 14:37

score 1 · Answer 1 · answered Nov 05 '20 at 14:04

You should custom TypeAdapter for serialize and deserialize Uri.

class UriTypeAdapter : TypeAdapter<Uri>() {
    override fun write(out: JsonWriter?, value: Uri?) {
        value?.let {
            out?.value(it.toString())
        } ?: run {
            out?.nullValue()
        }
    }

    override fun read(reader: JsonReader?): Uri {
        return if (reader?.peek() == JsonToken.NULL) {
            reader.nextNull()
            Uri.EMPTY
        } else {
            val uriString = reader?.nextString()
            uriString?.let {
                Uri.parse(it)
            } ?: run {
                Uri.EMPTY
            }
        }
    }
}

and setup Gson like this:

val gson = GsonBuilder()
    .registerTypeHierarchyAdapter(Uri::class.java, UriTypeAdapter())
    .create()

Thank you for the detailed explanation. I'll apply it usefully! — Ddophi, Nov 06 '20 at 14:39

How to load data class that include MutableList from SharedPreference?

1 Answers1