fix crashes due to race conditions when changing data source

app/src/main/java/net/vonforst/evmap/storage/ChargeLocationsDao.kt

@@ -10,6 +10,7 @@ import com.car2go.maps.model.LatLngBounds
 import kotlinx.coroutines.CoroutineScope
 import net.vonforst.evmap.api.ChargepointApi
 import net.vonforst.evmap.api.StringProvider
+import net.vonforst.evmap.api.goingelectric.GEReferenceData
 import net.vonforst.evmap.api.goingelectric.GoingElectricApiWrapper
 import net.vonforst.evmap.api.openchargemap.OpenChargeMapApiWrapper
 import net.vonforst.evmap.model.ChargeLocation
@@ -38,29 +39,31 @@ class ChargeLocationsRepository(
 ) {
     val api = MutableLiveData<ChargepointApi<ReferenceData>>().apply { value = api }
 
-    val referenceData = this.api.switchMap {
-        when (it) {
+    private val apiAndReferenceData = this.api.switchMap { api ->
+        when (api) {
             is GoingElectricApiWrapper -> {
                 GEReferenceDataRepository(
-                    it,
+                    api,
                     scope,
                     db.geReferenceDataDao(),
                     prefs
-                ).getReferenceData()
+                ).getReferenceData().map { api to it }
             }
             is OpenChargeMapApiWrapper -> {
                 OCMReferenceDataRepository(
-                    it,
+                    api,
                     scope,
                     db.ocmReferenceDataDao(),
                     prefs
-                ).getReferenceData()
+                ).getReferenceData().map { api to it }
             }
             else -> {
                 throw RuntimeException("no reference data implemented")
             }
         }
     }
+    val referenceData = apiAndReferenceData.map { it.second }
+
     private val chargeLocationsDao = db.chargeLocationsDao()
 
     fun getChargepoints(
@@ -68,9 +71,8 @@ class ChargeLocationsRepository(
         zoom: Float,
         filters: FilterValues?
     ): LiveData<Resource<List<ChargepointListItem>>> {
-        val api = api.value!!
         return liveData {
-            val refData = referenceData.await()
+            val (api, refData) = apiAndReferenceData.await()
             val result = api.getChargepoints(refData, bounds, zoom, filters)
 
             emit(result)
@@ -83,11 +85,9 @@ class ChargeLocationsRepository(
         zoom: Float,
         filters: FilterValues?
     ): LiveData<Resource<List<ChargepointListItem>>> {
-        val api = api.value!!
         return liveData {
-            val refData = referenceData.await()
-            val result =
-                api.getChargepointsRadius(refData, location, radius, zoom, filters)
+            val (api, refData) = apiAndReferenceData.await()
+            val result = api.getChargepointsRadius(refData, location, radius, zoom, filters)
 
             emit(result)
         }
@@ -97,13 +97,25 @@ class ChargeLocationsRepository(
         id: Long
     ): LiveData<Resource<ChargeLocation>> {
         return liveData {
-            val refData = referenceData.await()
-            val result = api.value!!.getChargepointDetail(refData, id)
+            val (api, refData) = apiAndReferenceData.await()
+            val result = api.getChargepointDetail(refData, id)
             emit(result)
         }
     }
 
-    fun getFilters(sp: StringProvider) = referenceData.map { data ->
-        api.value!!.getFilters(data, sp)
+    fun getFilters(sp: StringProvider) = apiAndReferenceData.map { (api, refData) ->
+        api.getFilters(refData, sp)
+    }
+
+    val chargeCardMap by lazy {
+        apiAndReferenceData.map { (_, refData) ->
+            if (refData is GEReferenceData) {
+                refData.chargecards.associate {
+                    it.id to it.convert()
+                }
+            } else {
+                null
+            }
+        }
     }
 }

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

@@ -14,7 +14,6 @@ import net.vonforst.evmap.api.availability.ChargeLocationStatus
 import net.vonforst.evmap.api.availability.getAvailability
 import net.vonforst.evmap.api.createApi
 import net.vonforst.evmap.api.goingelectric.GEChargepoint
-import net.vonforst.evmap.api.goingelectric.GEReferenceData
 import net.vonforst.evmap.api.openchargemap.OCMConnection
 import net.vonforst.evmap.api.openchargemap.OCMReferenceData
 import net.vonforst.evmap.api.stringProvider
@@ -83,20 +82,7 @@ class MapViewModel(application: Application, private val state: SavedStateHandle
         db.filterProfileDao().getProfiles(prefs.dataSource)
     }
 
-    val chargeCardMap: LiveData<Map<Long, ChargeCard>> by lazy {
-        MediatorLiveData<Map<Long, ChargeCard>>().apply {
-            value = null
-            addSource(repo.referenceData) { data ->
-                value = if (data is GEReferenceData) {
-                    data.chargecards.map {
-                        it.id to it.convert()
-                    }.toMap()
-                } else {
-                    null
-                }
-            }
-        }
-    }
+    val chargeCardMap = repo.chargeCardMap
 
     val filtersCount: LiveData<Int> by lazy {
         MediatorLiveData<Int>().apply {

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

@@ -109,7 +109,8 @@ fun <T> throttleLatest(
 public suspend fun <T> LiveData<T>.await(): T {
     return suspendCancellableCoroutine { continuation ->
         val observer = object : Observer<T> {
-            override fun onChanged(value: T) {
+            override fun onChanged(value: T?) {
+                if (value == null) return
                 removeObserver(this)
                 continuation.resume(value, null)
             }