Reduce memory usage for tile layers

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

@@ -9,6 +9,7 @@
 import android.content.pm.ApplicationInfo;
 import android.location.LocationManager;
 import android.os.Bundle;
+import android.os.Debug;
 import android.util.Log;
 import android.view.MenuItem;
 import android.view.View;
@@ -94,7 +95,8 @@ String getDebugText(String eol) {
         builder.append("Target SDK: " + appInfo.targetSdkVersion + eol);
 
         builder.append("Maximum avaliable memory " + Runtime.getRuntime().maxMemory() + eol);
-        builder.append("Total memory used " + Runtime.getRuntime().totalMemory() + eol);
+        builder.append("Total memory used (non-native) " + Runtime.getRuntime().totalMemory() + eol);
+        builder.append("Native memory usage " + Debug.getNativeHeapAllocatedSize() + eol);
         Logic logic = App.getLogic();
         if (logic != null) {
             Map map = logic.getMap();

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

@@ -310,6 +310,14 @@ public void setUpLayers(@NonNull Context ctx) {
             mLayers.clear();
             mLayers.addAll(tempLayers);
         }
+        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
+            // check memory usage and zap caches if necessary
+            // Android 8 and later allocate Bitmap storage natively
+            Runtime runtime = Runtime.getRuntime();
+            if (runtime.totalMemory() > runtime.maxMemory() / 2) {
+                flushInvisibleImageryCaches();
+            }
+        }
     }
 
     /**
@@ -438,6 +446,27 @@ public boolean isVisible(@NonNull MapViewLayer layer) {
         return false;
     }
 
+    /**
+     * Flush the in memory caches for all imagery layers except the top one if it is visible
+     */
+    public void flushInvisibleImageryCaches() {
+        List<MapViewLayer> layers = new ArrayList<>();
+        synchronized (mLayers) {
+            layers.addAll(mLayers);
+        }
+        Collections.reverse(layers);
+        boolean seenTop = false;
+        for (MapViewLayer l : layers) {
+            if (l.getType() == LayerType.IMAGERY) {
+                if (!l.isVisible() || seenTop) {
+                    ((MapTilesLayer<?>) l).flushTileCache(null, false);
+                } else {
+                    seenTop = true;
+                }
+            }
+        }
+    }
+
     /**
      * Return the current (that is top visible) background layer
      * 

src/main/java/de/blau/android/resources/WmsEndpointDatabaseView.java

@@ -191,7 +191,7 @@ private String sanitize(@NonNull String url) {
             Uri.Builder uriBuilder = uri.buildUpon();
             uriBuilder.clearQuery();
             for (String n : uri.getQueryParameterNames()) {
-                if (!"request".equalsIgnoreCase(n) && !"service".equalsIgnoreCase(n)) {
+                if (!"".equals(n) && !"request".equalsIgnoreCase(n) && !"service".equalsIgnoreCase(n)) {
                     uriBuilder.appendQueryParameter(n, uri.getQueryParameter(n));
                 }
             }

src/main/java/de/blau/android/views/layers/MapTilesLayer.java

@@ -3,6 +3,7 @@
 import java.io.IOException;
 import java.util.BitSet;
 import java.util.Collection;
+import java.util.Random;
 
 import android.content.ActivityNotFoundException;
 import android.content.Context;
@@ -116,6 +117,8 @@ public class MapTilesLayer<T> extends MapViewLayer implements ExtentInterface, L
 
     private final ViewBox viewBox = new ViewBox();
 
+    private final Random random = new Random();
+
     private final TileRenderer<T> mTileRenderer;
 
     // avoid creating new Rects in onDraw
@@ -388,8 +391,8 @@ protected void onDraw(Canvas c, IMapView osmv) {
             Snack.toastTopWarning(ctx, ctx.getString(R.string.toast_tile_layer_errors, myRendererInfo.getName()));
         }
 
-        long owner = (long) (Math.random() * Long.MAX_VALUE); // unique values so that we can track in the cache which
-                                                              // invocation of onDraw the tile belongs too
+        long owner = random.nextLong(); // unique values so that we can track in the cache which
+                                        // invocation of onDraw the tile belongs too
 
         int maxZoom = myRendererInfo.getMaxZoomLevel();
         int minZoom = myRendererInfo.getMinZoomLevel();

src/main/java/de/blau/android/views/util/LRUMapTileCache.java

@@ -112,7 +112,7 @@ public LRUMapTileCache(final long maxCacheSize) {
     // ===========================================================
 
     /**
-     * Overrides clear() to also clear the LRU list.
+     * Empty all data structures
      */
     public synchronized void clear() {
         for (CacheElement<T> ce : cache.values()) {
@@ -123,6 +123,7 @@ public synchronized void clear() {
         }
         cache.clear();
         list.clear();
+        cacheSize = 0;
     }
 
     /**