work on screenLayout

android/app/src/main/java/com/reactnativenavigation/controllers/NavigationActivity.java

 import android.os.Bundle;
 import android.support.v7.app.AppCompatActivity;
 import android.view.KeyEvent;
+import android.view.View;
 
 import com.facebook.react.modules.core.DefaultHardwareBackBtnHandler;
 import com.reactnativenavigation.NavigationApplication;
+import com.reactnativenavigation.layouts.Layout;
 import com.reactnativenavigation.layouts.SingleScreenLayout;
 import com.reactnativenavigation.params.ActivityParams;
 import com.reactnativenavigation.params.parsers.ActivityParamsParser;
     private static Activity currentActivity;
     private ActivityParams activityParams;
     private ModalController modalController;
-    private SingleScreenLayout singleScreenLayout;
+    private Layout layout;
 
     @Override
     protected void onCreate(Bundle savedInstanceState) {
     }
 
     private void createLayout() {
-        singleScreenLayout = new SingleScreenLayout(this, activityParams.screenParams);
-        setContentView(singleScreenLayout);
+        //TODO layout factory (tabsLayout etc)
+        layout = new SingleScreenLayout(this, activityParams.screenParams);
+        setContentView((View) layout);
     }
 
     @Override
     @Override
     protected void onDestroy() {
         modalController.onDestroy();
-//        layout.onDestroy();
+        layout.onDestroy();
         super.onDestroy();
         if (currentActivity == null || currentActivity.isFinishing()) {
             getNavigationReactInstance().onHostDestroy();
 
     @Override
     public void onJsDevReload() {
-        singleScreenLayout.removeAllReactViews();
+        layout.removeAllReactViews();
     }
 
     @Override
         if (modalController.onBackPressed()) {
             return;
         }
-//        if (layout.onBackPressed()) {
-//            return;
-//        }
+        if (layout.onBackPressed()) {
+            return;
+        }
         getNavigationReactInstance().onBackPressed();
     }
 

android/app/src/main/java/com/reactnativenavigation/layouts/BaseLayout.java

-package com.reactnativenavigation.layouts;
-
-public abstract class BaseLayout {
-
-//    private OnScreenPoppedListener onScreenPoppedListener;
-//
-//    private RnnToolBar toolBar;
-//    private ScreenStack screenStack;
-//
-//    public BaseLayout(Context context, _Screen initialScreen) {
-//        super(context);
-//        toolBar = (RnnToolBar) findViewById(R.id.toolbar);
-//        screenStack = (ScreenStack) findViewById(R.id.screenStack);
-//
-//        toolBar.update(initialScreen);
-//        addInitialScreen(initialScreen);
-//    }
-//
-//    private void addInitialScreen(_Screen screen) {
-//        screenStack.push(screen, new RctView.OnDisplayedListener() {
-//            @Override
-//            public void onDisplayed() {
-//                Animation animation = AnimationUtils.loadAnimation(getContext(), R.anim.slide_up);
-//                setAnimation(animation);
-//                animate();
-//            }
-//        });
-//    }
-//
-//    @Override
-//    public void push(_Screen screen) {
-//        screenStack.push(screen);
-//    }
-//
-//    @Override
-//    public _Screen pop() {
-//        _Screen popped = screenStack.pop();
-//        if (onScreenPoppedListener != null) {
-//            onScreenPoppedListener.onScreenPopped(popped);
-//        }
-//        return popped;
-//    }
-//
-//    @Override
-//    public int getScreenCount() {
-//        return screenStack.getStackSize();
-//    }
-//
-//    @Override
-//    public void removeAllReactViews() {
-//        screenStack.removeAllReactViews();
-//    }
-//
-//    public void setOnScreenPoppedListener(OnScreenPoppedListener onScreenPoppedListener) {
-//        this.onScreenPoppedListener = onScreenPoppedListener;
-//    }
-}

android/app/src/main/java/com/reactnativenavigation/layouts/OnScreenPoppedListener.java

-package com.reactnativenavigation.layouts;
-
-
-public interface OnScreenPoppedListener {
-
-}

android/app/src/main/java/com/reactnativenavigation/layouts/Screen.java

+package com.reactnativenavigation.layouts;
+
+public interface Screen {
+    void removeAllReactViews();
+}

android/app/src/main/java/com/reactnativenavigation/layouts/ScreenLayout.java → android/app/src/main/java/com/reactnativenavigation/layouts/ScreenImpl.java

 import com.reactnativenavigation.utils.SdkSupports;
 import com.reactnativenavigation.views.ContentView;
 import com.reactnativenavigation.views.ScrollDirectionListener;
+import com.reactnativenavigation.views.TopBar;
 
 import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
 import static android.view.ViewGroup.LayoutParams.WRAP_CONTENT;
 
-public class ScreenLayout extends LinearLayout implements ScrollDirectionListener.OnScrollChanged, Layout {
+public class ScreenImpl extends LinearLayout implements Screen, ScrollDirectionListener.OnScrollChanged {
 
     private final ScreenParams screenParams;
     private ContentView contentView;
     private TopBar topBar;
 
-    public ScreenLayout(Context context, ScreenParams screenParams) {
+    public ScreenImpl(Context context, ScreenParams screenParams) {
         super(context);
         this.screenParams = screenParams;
         setOrientation(VERTICAL);
 
     @Override
     public void onScrollChanged(ScrollDirectionListener.Direction direction) {
-
-    }
-
-    @Override
-    public boolean onBackPressed() {
-        return false;
-    }
-
-    @Override
-    public void onDestroy() {
-
+        // TODO handle if needed
     }
 
     @Override

android/app/src/main/java/com/reactnativenavigation/layouts/ScreenStack.java

+package com.reactnativenavigation.layouts;
+
+import android.animation.LayoutTransition;
+import android.content.Context;
+import android.view.View;
+import android.widget.FrameLayout;
+
+import com.reactnativenavigation.params.ScreenParams;
+
+import java.util.Stack;
+
+import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
+
+public class ScreenStack extends FrameLayout {
+    private Stack<Screen> stack = new Stack<>();
+
+    public ScreenStack(Context context, ScreenParams initialScreenParams) {
+        super(context);
+        setLayoutTransition(new LayoutTransition());
+        push(initialScreenParams);
+    }
+
+    public void push(ScreenParams screenParams) {
+        Screen screen = new ScreenImpl(getContext(), screenParams);
+        addView((View) screen, new FrameLayout.LayoutParams(MATCH_PARENT, MATCH_PARENT));
+        stack.push(screen);
+    }
+
+    public Screen pop() {
+        return stack.pop();
+    }
+
+    public void popToRoot() {
+        while (getStackSize() > 1) {
+            pop();
+        }
+    }
+
+    public void destroy() {
+        while (!isEmpty()) {
+            Screen screen = pop();
+            screen.removeAllReactViews();
+        }
+        removeAllViews();
+    }
+
+    public boolean isEmpty() {
+        return stack.isEmpty();
+    }
+
+    public int getStackSize() {
+        return stack.size();
+    }
+
+    public Screen peek() {
+        return stack.peek();
+    }
+
+
+//    /**
+//     * Remove the ScreenStack from {@code parent} while preventing all child react views from getting unmounted
+//        -= USE WHEN SWITCHING TABS =-
+//     */
+//    public void removeFromScreen(ViewGroup parent) {
+//        mStack.peek().view.onTemporallyRemovedFromScreen();
+//
+//        parent.removeView(this);
+//    }
+//    /**
+//     * Add ScreenStack to {@code parent}
+//       -= USE WHEN SWITCHING TABS =-
+//     */
+//    public void addToScreen(ViewGroup parent) {
+//        mStack.peek().view.onReAddToScreen();
+//
+//        parent.addView(this, new CoordinatorLayout.LayoutParams(MATCH_PARENT, MATCH_PARENT));
+//    }
+}

android/app/src/main/java/com/reactnativenavigation/layouts/SingleScreenLayout.java

 public class SingleScreenLayout extends FrameLayout implements Layout {
 
     private final ScreenParams screenParams;
-    private ScreenLayout screenLayout;
+    private ScreenStack stack;
 
     public SingleScreenLayout(Context context, ScreenParams screenParams) {
         super(context);
         this.screenParams = screenParams;
-        createLayout();
+        createStack(context);
     }
 
-    private void createLayout() {
-        screenLayout = new ScreenLayout(getContext(), screenParams);
-        addView(screenLayout, new FrameLayout.LayoutParams(MATCH_PARENT, MATCH_PARENT));
+    private void createStack(Context context) {
+        if (stack != null) {
+            stack.destroy();
+        }
+        stack = new ScreenStack(context, screenParams);
+        addView(stack, new LayoutParams(MATCH_PARENT, MATCH_PARENT));
     }
 
     @Override
     public boolean onBackPressed() {
-        return false;
+        if (stack.isEmpty()) {
+            return false;
+        } else {
+            stack.pop();
+            return true;
+        }
     }
 
     @Override
     public void onDestroy() {
-
+        stack.destroy();
     }
 
     @Override
     public void removeAllReactViews() {
-        screenLayout.removeAllReactViews();
+        stack.destroy();
     }
 }

android/app/src/main/java/com/reactnativenavigation/layouts/TopBar.java → android/app/src/main/java/com/reactnativenavigation/views/TopBar.java

-package com.reactnativenavigation.layouts;
+package com.reactnativenavigation.views;
 
 import android.content.Context;
 import android.support.design.widget.AppBarLayout;
 
 import com.reactnativenavigation.params.TitleBarButtonParams;
-import com.reactnativenavigation.views.TitleBar;
 
 import java.util.List;