Only set elevation values from Options

This fixes a bug which occurred when returning from background - sometimes the system would set
an unexpected elevation value which seems like the default elevation.
This commit checks if the new elevation value was specified by RNN before setting it.

lib/android/app/src/main/java/com/reactnativenavigation/views/topbar/TopBar.java

     private FrameLayout root;
     private View border;
     private View component;
+    private float elevation = -1;
 
     public TopBar(final Context context, StackLayout parentView) {
         super(context);
 
     public void setTopTabsHeight(int height) {
         if (topTabs.getLayoutParams().height == height) return;
-        topTabs.getLayoutParams().height = height > 0 ? (int) UiUtils.dpToPx(getContext(), height) : height;
+        topTabs.getLayoutParams().height = height > 0 ? UiUtils.dpToPx(getContext(), height) : height;
         topTabs.setLayoutParams(topTabs.getLayoutParams());
     }
 
     }
 
     public void setElevation(Double elevation) {
-        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP &&
-                getElevation() != elevation.floatValue()) {
-            setElevation(UiUtils.dpToPx(getContext(), elevation.floatValue()));
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP && getElevation() != elevation.floatValue()) {
+            this.elevation = UiUtils.dpToPx(getContext(), elevation.floatValue());
+            setElevation(this.elevation);
         }
     }
 
+    @Override
+    public void setElevation(float elevation) {
+        if (elevation == this.elevation) super.setElevation(elevation);
+    }
+
     public Toolbar getTitleBar() {
         return titleBar;
     }

lib/android/app/src/test/java/com/reactnativenavigation/views/TopBarTest.java

 import com.reactnativenavigation.BaseTest;
 import com.reactnativenavigation.anim.TopBarAnimator;
 import com.reactnativenavigation.parse.AnimationOptions;
+import com.reactnativenavigation.utils.UiUtils;
 import com.reactnativenavigation.viewcontrollers.topbar.TopBarController;
 import com.reactnativenavigation.views.topbar.TopBar;
 
 import org.junit.Test;
+import org.robolectric.annotation.Config;
 
 import static org.assertj.core.api.Java6Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
+@Config(qualifiers = "xxhdpi")
 public class TopBarTest extends BaseTest {
 
     private TopBar uut;
     private TopBarAnimator animator;
+    private Activity activity;
 
     @SuppressWarnings("Convert2Lambda")
     @Override
     public void beforeEach() {
-        Activity activity = newActivity();
+        activity = newActivity();
         StackLayout parent = new StackLayout(activity, new TopBarController(), null);
         uut = new TopBar(activity, parent);
         animator = spy(new TopBarAnimator(uut));
         uut.showAnimate(options);
         verify(animator, times(1)).show(options);
     }
+
+    @Test
+    public void setElevation_ignoreValuesNotSetByNavigation() {
+        float initialElevation = uut.getElevation();
+        uut.setElevation(1f);
+        assertThat(uut.getElevation()).isEqualTo(initialElevation);
+
+        uut.setElevation(Double.valueOf(2));
+        assertThat(uut.getElevation()).isEqualTo(UiUtils.dpToPx(activity, 2));
+    }
 }