keep ChargerDetails in saved state

fixes #205

app/src/main/java/net/vonforst/evmap/viewmodel/MapViewModel.kt

@@ -141,17 +141,24 @@ class MapViewModel(application: Application, private val state: SavedStateHandle
     }
     val chargerDetails: MediatorLiveData<Resource<ChargeLocation>> by lazy {
         MediatorLiveData<Resource<ChargeLocation>>().apply {
+            value = state["chargerDetails"]
             listOf(chargerSparse, referenceData).forEach {
                 addSource(it) { _ ->
                     val charger = chargerSparse.value
                     val refData = referenceData.value
                     if (charger != null && refData != null) {
-                        loadChargerDetails(charger, refData)
+                        if (charger.id != value?.data?.id) {
+                            loadChargerDetails(charger, refData)
+                        }
                     } else {
                         value = null
                     }
                 }
             }
+            observeForever {
+                // persist data in case fragment gets recreated
+                state["chargerDetails"] = it
+            }
         }
     }
     val charger: MediatorLiveData<Resource<ChargeLocation>> by lazy {

app/src/main/java/net/vonforst/evmap/viewmodel/Utils.kt

@@ -1,5 +1,6 @@
 package net.vonforst.evmap.viewmodel
 
+import android.os.Parcelable
 import androidx.annotation.MainThread
 import androidx.annotation.Nullable
 import androidx.lifecycle.*
@@ -7,6 +8,8 @@ import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
+import kotlinx.parcelize.Parcelize
+import kotlinx.parcelize.RawValue
 import java.util.concurrent.atomic.AtomicBoolean
 
 
@@ -24,9 +27,13 @@ enum class Status {
 
 /**
  * A generic class that holds a value with its loading status.
- * @param <T>
-</T> */
-data class Resource<out T>(val status: Status, val data: T?, val message: String?) {
+ *
+ * Note that this class implements Parcelable for convenience, but will give a runtime error when
+ * trying to write it to a Parcel if the type parameter does not implement Parcelable.
+ */
+@Parcelize
+data class Resource<out T>(val status: Status, val data: @RawValue T?, val message: String?) :
+    Parcelable {
     companion object {
         fun <T> success(data: T?): Resource<T> {
             return Resource(Status.SUCCESS, data, null)