Don't force recreating the map object and associated layer state

If Main has been destroyed, both the Map and Logic objects may still be
available and current, so we now reuse them instead of forcing
recreation.

This resolves race conditions that could be caused by selecting and
loading files into layers via the system file picker that could lead to
Main being removed.

src/main/java/de/blau/android/Main.java

@@ -67,6 +67,7 @@
 import android.view.View.OnLongClickListener;
 import android.view.View.OnTouchListener;
 import android.view.ViewGroup;
+import android.view.ViewParent;
 import android.view.ViewStub;
 import android.widget.LinearLayout;
 import android.widget.RelativeLayout;
@@ -492,13 +493,17 @@ protected void onCreate(final Bundle savedInstanceState) {
         LinearLayout ml = (LinearLayout) getLayoutInflater().inflate(layout, null);
         mapLayout = (RelativeLayout) ml.findViewById(R.id.mainMap);
 
-        if (map != null) {
-            Log.d(DEBUG_TAG, "map exists .. destroying");
-            map.onDestroy();
+        Logic logic = App.getLogic(); // logic instance might still be around
+        map = logic != null ? logic.getMap() : null;
+        if (map == null) {
+            map = new Map(this);
+            map.setId(R.id.map_view);
+        } else {
+            ViewGroup parent = (ViewGroup) map.getParent();
+            if (parent != null) {
+                parent.removeView(map);
+            }
         }
-        map = new Map(this);
-        map.setId(R.id.map_view);
-
         // Register some Listener
         mapTouchListener = new MapTouchListener();
         map.setOnTouchListener(mapTouchListener);
@@ -585,14 +590,14 @@ protected void onCreate(final Bundle savedInstanceState) {
 
         loadOnResume = false;
 
-        if (App.getLogic() == null) {
+        if (logic == null) {
             Log.i(DEBUG_TAG, "onCreate - creating new logic");
-            App.newLogic();
+            logic = App.newLogic();
         }
         Log.i(DEBUG_TAG, "onCreate - setting new map");
 
-        App.getLogic().setPrefs(prefs);
-        App.getLogic().setMap(map, true);
+        logic.setPrefs(prefs);
+        logic.setMap(map, true);
 
         Log.d(DEBUG_TAG, "StorageDelegator dirty is " + App.getDelegator().isDirty());
         if (StorageDelegator.isStateAvailable(this) && !App.getDelegator().isDirty()) {
@@ -806,7 +811,7 @@ public void onError(@Nullable AsyncResult result) {
                     // loadStateFromFile does this above
                     App.getLogic().loadEditingState(this, setViewBox);
                 }
-                logic.loadLayerState(this, postLoadTasks);
+                // layer state should still be available if logic is still around, no need to load
                 map.invalidate();
                 checkPermissions(() -> {
                     postLoadData.onSuccess();

src/main/java/de/blau/android/Map.java

@@ -427,7 +427,7 @@ public MapViewLayer getLayer(int index) {
             if (index >= 0 && index < mLayers.size()) {
                 return mLayers.get(index);
             }
-            Log.e(DEBUG_TAG, "Layer for index " + index + " is null");
+            Log.e(DEBUG_TAG, "Layer for index " + index + " is null " + mLayers.size() + " layers total");
             return null;
         }
     }

src/main/java/de/blau/android/dialogs/Layers.java

@@ -420,7 +420,8 @@ protected Void doInBackground(Void param) {
      * @param map current Map
      * @param type the layer type
      */
-    private void addStyleableLayerFromFile(final FragmentActivity activity, final Preferences prefs, final Map map, @NonNull final LayerType type) {
+    private void addStyleableLayerFromFile(@NonNull final FragmentActivity activity, @NonNull final Preferences prefs, @NonNull final Map map,
+            @NonNull final LayerType type) {
         Log.d(DEBUG_TAG, "addStyleableLayerFromFile");
         SelectFile.read(activity, R.string.config_osmPreferredDir_key, new ReadFile() {
             private static final long serialVersionUID = 1L;