Add back button to pushed screens

lib/android/app/src/main/java/com/reactnativenavigation/react/Constants.java

+package com.reactnativenavigation.react;
+
+public class Constants {
+    public static final String BACK_BUTTON_ID = "RNN.back";
+}

lib/android/app/src/main/java/com/reactnativenavigation/utils/CollectionUtils.java

+package com.reactnativenavigation.utils;
+
+import java.util.Collection;
+
+public class CollectionUtils {
+    public static boolean isNullOrEmpty(Collection collection) {
+        return collection == null || collection.isEmpty();
+    }
+}

lib/android/app/src/main/java/com/reactnativenavigation/utils/ImageLoader.java

     public interface ImagesLoadingListener {
         void onComplete(@NonNull List<Drawable> drawable);
 
+        void onComplete(@NonNull Drawable drawable);
+
         void onError(Throwable error);
     }
 
     private static final String FILE_SCHEME = "file";
 
+    public void loadIcon(Context context, String uri, ImagesLoadingListener listener) {
+        try {
+            listener.onComplete(getDrawable(context, uri));
+        } catch (IOException e) {
+            listener.onError(e);
+        }
+    }
 
     public void loadIcons(final Context context, List<String> uris, ImagesLoadingListener listener) {
         try {

lib/android/app/src/main/java/com/reactnativenavigation/utils/ImageLoadingListenerAdapter.java

 
     }
 
+    @Override
+    public void onComplete(@NonNull Drawable drawable) {
+
+    }
+
     @Override
     public void onError(Throwable error) {
         error.printStackTrace();

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/StackController.java

 
 import com.reactnativenavigation.anim.NavigationAnimator;
 import com.reactnativenavigation.parse.Options;
+import com.reactnativenavigation.parse.params.Button;
+import com.reactnativenavigation.react.Constants;
 import com.reactnativenavigation.utils.CommandListener;
 import com.reactnativenavigation.utils.CommandListenerAdapter;
 import com.reactnativenavigation.viewcontrollers.topbar.TopBarBackgroundViewController;
 import com.reactnativenavigation.views.titlebar.TitleBarReactViewCreator;
 import com.reactnativenavigation.views.topbar.TopBar;
 
+import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.Iterator;
 
 import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
         final ViewController toRemove = stack.peek();
         child.setParentController(this);
         stack.push(child.getId(), child);
+        addBackButton(child);
         getView().addView(child.getView(), MATCH_PARENT, MATCH_PARENT);
 
         if (toRemove != null) {
         }
     }
 
+    private void addBackButton(ViewController child) {
+        if (size() <= 1 || child.options.topBar.leftButtons != null) return;
+        Options options = new Options();
+        Button back = new Button();
+        back.id = Constants.BACK_BUTTON_ID;
+        options.topBar.leftButtons = new ArrayList<>(Collections.singleton(back));
+        child.mergeOptions(options);
+    }
+
     public void setRoot(ViewController child, CommandListener listener) {
         push(child, new CommandListenerAdapter() {
             @Override
         return stack.size() > 1;
     }
 
+    @NonNull
     @Override
-    public void sendOnNavigationButtonPressed(String buttonId) {
-        peek().sendOnNavigationButtonPressed(buttonId);
+    protected StackLayout createView() {
+        return new StackLayout(getActivity(),
+                topBarButtonCreator,
+                titleBarReactViewCreator,
+                topBarBackgroundViewController,
+                topBarController,
+                this::onNavigationButtonPressed,
+                getId()
+        );
+    }
+
+    private void onNavigationButtonPressed(String buttonId) {
+        if (Constants.BACK_BUTTON_ID.equals(buttonId)) {
+            pop(new CommandListenerAdapter());
+        } else {
+            sendOnNavigationButtonPressed(buttonId);
+        }
     }
 
-    @NonNull
     @Override
-    protected StackLayout createView() {
-        return new StackLayout(getActivity(), topBarButtonCreator, titleBarReactViewCreator, topBarBackgroundViewController, topBarController, this::sendOnNavigationButtonPressed, getId());
+    public void sendOnNavigationButtonPressed(String buttonId) {
+        peek().sendOnNavigationButtonPressed(buttonId);
     }
 
     @NonNull

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/TopBarButtonController.java

 package com.reactnativenavigation.viewcontrollers;
 
+import android.annotation.SuppressLint;
 import android.app.Activity;
 import android.graphics.Color;
 import android.graphics.drawable.Drawable;
 import android.support.annotation.NonNull;
 import android.support.v7.widget.ActionMenuView;
 import android.support.v7.widget.Toolbar;
-import android.util.Log;
 import android.view.MenuItem;
 import android.widget.ImageButton;
 import android.widget.TextView;
 import com.reactnativenavigation.utils.ImageLoadingListenerAdapter;
 import com.reactnativenavigation.utils.UiUtils;
 import com.reactnativenavigation.utils.ViewUtils;
+import com.reactnativenavigation.viewcontrollers.button.NavigationIconResolver;
 import com.reactnativenavigation.views.titlebar.TitleBarReactButtonView;
 
 import java.util.Collections;
         void onPress(String buttonId);
     }
 
+    private final NavigationIconResolver navigationIconResolver;
     private final ImageLoader imageLoader;
     private ButtonOptionsPresenter optionsPresenter;
     private final Button button;
     private TopBarButtonController.OnClickListener onPressListener;
     private Drawable icon;
 
-    public TopBarButtonController(Activity activity, ImageLoader imageLoader, ButtonOptionsPresenter optionsPresenter, Button button, ReactViewCreator viewCreator, OnClickListener onClickListener) {
+    public TopBarButtonController(Activity activity, NavigationIconResolver navigationIconResolver, ImageLoader imageLoader, ButtonOptionsPresenter optionsPresenter, Button button, ReactViewCreator viewCreator, OnClickListener onClickListener) {
         super(activity, button.id, new Options());
+        this.navigationIconResolver = navigationIconResolver;
         this.imageLoader = imageLoader;
         this.optionsPresenter = optionsPresenter;
         this.button = button;
         this.onPressListener = onClickListener;
     }
 
+    @SuppressLint("MissingSuperCall")
     @Override
     public void onViewAppeared() {
         view.sendComponentStart();
     }
 
+    @SuppressLint("MissingSuperCall")
     @Override
     public void onViewDisappear() {
         view.sendComponentStop();
     }
 
     public void applyNavigationIcon(Toolbar toolbar) {
-        if (!button.hasIcon()) {
-            Log.w("RNN", "Left button needs to have an icon");
-            return;
-        }
-
-        imageLoader.loadIcons(toolbar.getContext(), Collections.singletonList(button.icon.get()), new ImageLoader.ImagesLoadingListener() {
-            @Override
-            public void onComplete(@NonNull List<Drawable> drawables) {
-                icon = drawables.get(0);
-                setIconColor(icon);
-                toolbar.setNavigationOnClickListener(view -> onPressListener.onPress(button.id));
-                toolbar.setNavigationIcon(icon);
-                setLeftButtonTestId(toolbar);
-            }
-
-            @Override
-            public void onError(Throwable error) {
-                error.printStackTrace();
-            }
+        navigationIconResolver.resolve(button, icon -> {
+            setIconColor(icon);
+            toolbar.setNavigationOnClickListener(view -> onPressListener.onPress(button.id));
+            toolbar.setNavigationIcon(icon);
+            setLeftButtonTestId(toolbar);
         });
     }
 

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/bottomtabs/BottomTabsController.java

 import com.reactnativenavigation.react.EventEmitter;
 import com.reactnativenavigation.utils.CommandListener;
 import com.reactnativenavigation.utils.ImageLoader;
+import com.reactnativenavigation.utils.ImageLoadingListenerAdapter;
 import com.reactnativenavigation.viewcontrollers.ChildControllersRegistry;
 import com.reactnativenavigation.viewcontrollers.ParentController;
 import com.reactnativenavigation.viewcontrollers.ViewController;
             icons.add(tabOptions.icon.get());
         }
 
-        imageLoader.loadIcons(getActivity(), icons, new ImageLoader.ImagesLoadingListener() {
+        imageLoader.loadIcons(getActivity(), icons, new ImageLoadingListenerAdapter() {
 
             @Override
             public void onComplete(@NonNull List<Drawable> drawables) {

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/button/NavigationIconResolver.java

+package com.reactnativenavigation.viewcontrollers.button;
+
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.support.annotation.NonNull;
+import android.support.v4.content.ContextCompat;
+
+import com.reactnativenavigation.R;
+import com.reactnativenavigation.parse.params.Button;
+import com.reactnativenavigation.react.Constants;
+import com.reactnativenavigation.utils.ImageLoader;
+import com.reactnativenavigation.utils.ImageLoadingListenerAdapter;
+import com.reactnativenavigation.utils.Task;
+
+public class NavigationIconResolver {
+
+    private Context context;
+    private ImageLoader imageLoader;
+
+    public NavigationIconResolver(Context context, ImageLoader imageLoader) {
+        this.context = context;
+        this.imageLoader = imageLoader;
+    }
+
+    public void resolve(Button button, Task<Drawable> onSuccess) {
+        if (button.icon.hasValue()) {
+            imageLoader.loadIcon(context, button.icon.get(), new ImageLoadingListenerAdapter() {
+                @Override
+                public void onComplete(@NonNull Drawable icon) {
+                    onSuccess.run(icon);
+                }
+
+                @Override
+                public void onError(Throwable error) {
+                    throw new RuntimeException(error);
+                }
+            });
+        } else if (Constants.BACK_BUTTON_ID.equals(button.id)) {
+            onSuccess.run(ContextCompat.getDrawable(context, R.drawable.ic_arrow_back_black_24dp));
+        } else {
+            throw new RuntimeException("Left button needs to have an icon");
+        }
+    }
+}

lib/android/app/src/main/java/com/reactnativenavigation/views/Fab.java

 import com.reactnativenavigation.anim.FabCollapseBehaviour;
 import com.reactnativenavigation.interfaces.ScrollEventListener;
 import com.reactnativenavigation.utils.ImageLoader;
+import com.reactnativenavigation.utils.ImageLoadingListenerAdapter;
 
 import java.util.Collections;
 import java.util.List;
     }
 
     public void applyIcon(String icon) {
-        new ImageLoader().loadIcons(getContext(), Collections.singletonList(icon), new ImageLoader.ImagesLoadingListener() {
+        new ImageLoader().loadIcons(getContext(), Collections.singletonList(icon), new ImageLoadingListenerAdapter() {
             @Override
             public void onComplete(@NonNull List<Drawable> drawables) {
                 setImageDrawable(drawables.get(0));

lib/android/app/src/main/java/com/reactnativenavigation/views/titlebar/TitleBar.java

 import com.reactnativenavigation.viewcontrollers.ReactViewCreator;
 import com.reactnativenavigation.viewcontrollers.TitleBarReactViewController;
 import com.reactnativenavigation.viewcontrollers.TopBarButtonController;
+import com.reactnativenavigation.viewcontrollers.button.NavigationIconResolver;
 
 import java.util.ArrayList;
 import java.util.List;
     }
 
     public TopBarButtonController createButtonController(Button button) {
-        return new TopBarButtonController((Activity) getContext(), new ImageLoader(), new ButtonOptionsPresenter(this, button), button, buttonCreator, onClickListener);
+        ImageLoader imageLoader = new ImageLoader();
+        return new TopBarButtonController((Activity) getContext(),
+                new NavigationIconResolver(getContext(), imageLoader),
+                imageLoader,
+                new ButtonOptionsPresenter(this, button),
+                button,
+                buttonCreator,
+                onClickListener
+        );
     }
 
     public Toolbar.LayoutParams getComponentLayoutParams(Component component) {

lib/android/app/src/main/res/drawable/ic_arrow_back_black_24dp.xml

+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:viewportWidth="24.0"
+        android:viewportHeight="24.0">
+    <path
+        android:fillColor="#FF000000"
+        android:pathData="M20,11H7.83l5.59,-5.59L12,4l-8,8 8,8 1.41,-1.41L7.83,13H20v-2z"/>
+</vector>

lib/android/app/src/test/java/com/reactnativenavigation/mocks/ImageLoaderMock.java

 
 import org.mockito.Mockito;
 
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
         ImageLoader imageLoader = Mockito.mock(ImageLoader.class);
         doAnswer(
                 invocation -> {
-                    int urlCount = ((List) invocation.getArguments()[1]).size();
+                    int urlCount = ((Collection) invocation.getArguments()[1]).size();
                     List<Drawable> drawables = Collections.nCopies(urlCount, mockDrawable);
                     ((ImageLoader.ImagesLoadingListener) invocation.getArguments()[2]).onComplete(drawables);
                     return null;
                 }
         ).when(imageLoader).loadIcons(any(), any(), any());
+        doAnswer(
+                invocation -> {
+                    ((ImageLoader.ImagesLoadingListener) invocation.getArguments()[2]).onComplete(mockDrawable);
+                    return null;
+                }
+        ).when(imageLoader).loadIcon(any(), any(), any());
         return imageLoader;
     }
 }

lib/android/app/src/test/java/com/reactnativenavigation/utils/OptionHelper.java

 import com.reactnativenavigation.parse.Options;
 import com.reactnativenavigation.parse.params.Text;
 
+import java.util.ArrayList;
+
 public class OptionHelper {
     public static Options createBottomTabOptions() {
         Options options = new Options();
+        options.topBar.leftButtons = new ArrayList<>();
         options.bottomTabOptions.title = new Text("Tab");
         options.bottomTabOptions.icon = new Text("http://127.0.0.1/icon.png");
         return options;

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/StackControllerTest.java

 import com.reactnativenavigation.parse.NestedAnimationsOptions;
 import com.reactnativenavigation.parse.Options;
 import com.reactnativenavigation.parse.params.Bool;
+import com.reactnativenavigation.parse.params.Button;
 import com.reactnativenavigation.parse.params.Text;
 import com.reactnativenavigation.utils.CommandListenerAdapter;
 import com.reactnativenavigation.utils.ViewHelper;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Mockito;
 
+import java.util.ArrayList;
+import java.util.Collections;
+
 import static org.assertj.core.api.Java6Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
         verify(listener, times(1)).onSuccess(child1.getId());
     }
 
+    @Test
+    public void push_backButtonIsAddedIfStackContainsMoreThenOneScreen() {
+        uut.push(child1, new CommandListenerAdapter());
+        verify(child1, times(0)).mergeOptions(any());
+
+        uut.push(child2, new CommandListenerAdapter());
+        ArgumentCaptor<Options> captor = ArgumentCaptor.forClass(Options.class);
+        verify(child2, times(1)).mergeOptions(captor.capture());
+        assertThat(captor.getValue().topBar.leftButtons).isNotNull();
+        assertThat(captor.getValue().topBar.leftButtons.get(0).id).isEqualTo("RNN.back");
+    }
+
+    @Test
+    public void push_backButtonIsNotAddedIfScreenContainsLeftButtons() {
+        uut.push(child1, new CommandListenerAdapter());
+
+        Button leftButton = new Button();
+        leftButton.id = "someButton";
+        child2.options.topBar.leftButtons = new ArrayList<>(Collections.singleton(leftButton));
+        uut.push(child2, new CommandListenerAdapter());
+        verify(child2, times(0)).mergeOptions(any());
+    }
+
+    @Test
+    public void push_backButtonIsNotAddedIfScreenClearsLeftButton() {
+        child1.options.topBar.leftButtons = new ArrayList<>();
+        uut.push(child1, new CommandListenerAdapter());
+        verify(child1, times(0)).mergeOptions(any());
+    }
+
     @Test
     public void animateSetRoot() {
         assertThat(uut.isEmpty()).isTrue();
         assertThat(uut.isEmpty()).isTrue();
         uut.push(child1, new CommandListenerAdapter());
         uut.push(child2, new CommandListenerAdapter());
+        assertThat(uut.getTopBar().getTitleBar().getNavigationIcon()).isNotNull();
         uut.setRoot(child3, new CommandListenerAdapter() {
             @Override
             public void onSuccess(String childId) {
                 assertContainsOnlyId(child3.getId());
+                assertThat(uut.getTopBar().getTitleBar().getNavigationIcon()).isNull();
             }
         });
     }
     @Test
     public void pop_layoutHandlesChildWillDisappear() {
         final StackLayout[] stackLayout = new StackLayout[1];
-        uut =
-                new StackControllerBuilder(activity)
+        uut = new StackControllerBuilder(activity)
                         .setTopBarButtonCreator(new TopBarButtonCreatorMock())
                         .setTitleBarReactViewCreator(new TitleBarReactViewCreatorMock())
                         .setTopBarBackgroundViewController(new TopBarBackgroundViewController(activity, new TopBarBackgroundViewCreatorMock()))
     }
 
     private StackController createStackController(String id) {
-        topBarController = spy(new TopBarController() {
-            @Override
-            protected TopBar createTopBar(Context context, ReactViewCreator buttonCreator, TitleBarReactViewCreator titleBarReactViewCreator, TopBarBackgroundViewController topBarBackgroundViewController, TopBarButtonController.OnClickListener topBarButtonClickListener, StackLayout stackLayout) {
-                TopBar topBar = spy(super.createTopBar(context, buttonCreator, titleBarReactViewCreator, topBarBackgroundViewController, topBarButtonClickListener, stackLayout));
-                return topBar;
-            }
-        });
+        createTopBarController();
         return new StackControllerBuilder(activity)
                 .setChildRegistry(childRegistry)
                 .setTopBarButtonCreator(new TopBarButtonCreatorMock())
                 .setInitialOptions(new Options())
                 .createStackController();
     }
+
+    private void createTopBarController() {
+        topBarController = spy(new TopBarController() {
+            @Override
+            protected TopBar createTopBar(Context context, ReactViewCreator buttonCreator, TitleBarReactViewCreator titleBarReactViewCreator, TopBarBackgroundViewController topBarBackgroundViewController, TopBarButtonController.OnClickListener topBarButtonClickListener, StackLayout stackLayout) {
+                return spy(super.createTopBar(context, buttonCreator, titleBarReactViewCreator, topBarBackgroundViewController, topBarButtonClickListener, stackLayout));
+            }
+        });
+    }
 }

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/TitleBarTest.java

 import com.reactnativenavigation.parse.Component;
 import com.reactnativenavigation.parse.params.Button;
 import com.reactnativenavigation.parse.params.Text;
+import com.reactnativenavigation.react.Constants;
 import com.reactnativenavigation.react.ReactView;
 import com.reactnativenavigation.utils.ViewUtils;
 import com.reactnativenavigation.views.titlebar.TitleBar;
 
     private void createButtons() {
         leftButton = new Button();
-        leftButton.id = "back";
-        leftButton.title = new Text("abc");
+        leftButton.id = Constants.BACK_BUTTON_ID;
 
         textButton = new Button();
         textButton.id = "textButton";
 
     @Test
     public void setRightButtons_destroysRightButtons() {
-        uut.setLeftButtons(leftButton(leftButton));
         uut.setRightButtons(rightButtons(customButton));
         uut.setLeftButtons(leftButton(leftButton));
         uut.setRightButtons(rightButtons(textButton));

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/TopBarButtonControllerTest.java

 import com.reactnativenavigation.parse.params.Number;
 import com.reactnativenavigation.parse.params.Text;
 import com.reactnativenavigation.utils.ButtonOptionsPresenter;
+import com.reactnativenavigation.viewcontrollers.button.NavigationIconResolver;
 import com.reactnativenavigation.viewcontrollers.topbar.TopBarBackgroundViewController;
 import com.reactnativenavigation.viewcontrollers.topbar.TopBarController;
 
         getTitleBar().layout(0, 0, 1080, 200);
 
         optionsPresenter = spy(new ButtonOptionsPresenter(getTitleBar(), button));
-        uut = new TopBarButtonController(activity, ImageLoaderMock.mock(), optionsPresenter, button, buttonCreatorMock, (buttonId) -> {});
+        uut = new TopBarButtonController(activity, new NavigationIconResolver(activity, ImageLoaderMock.mock()), ImageLoaderMock.mock(), optionsPresenter, button, buttonCreatorMock, (buttonId) -> {});
 
         stackController.ensureViewIsCreated();
     }

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/button/NavigationIconResolverTest.java

+package com.reactnativenavigation.viewcontrollers.button;
+
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+
+import com.reactnativenavigation.BaseTest;
+import com.reactnativenavigation.mocks.ImageLoaderMock;
+import com.reactnativenavigation.parse.params.Button;
+import com.reactnativenavigation.parse.params.Color;
+import com.reactnativenavigation.parse.params.Text;
+import com.reactnativenavigation.react.Constants;
+import com.reactnativenavigation.utils.ImageLoader;
+import com.reactnativenavigation.utils.Task;
+
+import org.junit.Test;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyZeroInteractions;
+
+public class NavigationIconResolverTest extends BaseTest {
+    private static final String ICON_URI = "someIconUri";
+    private NavigationIconResolver uut;
+    private ImageLoader imageLoader;
+    private Context context;
+
+    @Override
+    public void beforeEach() {
+        imageLoader = ImageLoaderMock.mock();
+        context = newActivity();
+        uut = new NavigationIconResolver(context, imageLoader);
+    }
+
+    @Test
+    public void create_iconButton() {
+        @SuppressWarnings("Convert2Lambda") Task<Drawable> onSuccess = spy(new Task<Drawable>() {
+            @Override
+            public void run(Drawable icon) {
+
+            }
+        });
+        uut.resolve(iconButton(), onSuccess);
+        verify(imageLoader).loadIcon(eq(context), eq(ICON_URI), any());
+        verify(onSuccess).run(any(Drawable.class));
+    }
+
+    @Test
+    public void create_backButton() {
+        @SuppressWarnings("Convert2Lambda") Task<Drawable> onSuccess = spy(new Task<Drawable>() {
+            @Override
+            public void run(Drawable param) {
+
+            }
+        });
+        uut.resolve(backButton(), onSuccess);
+        verifyZeroInteractions(imageLoader);
+        verify(onSuccess).run(any());
+    }
+
+    private Button iconButton() {
+        Button button = new Button();
+        button.id = "iconBtnId";
+        button.icon = new Text(ICON_URI);
+        button.color = new Color(android.graphics.Color.RED);
+        return button;
+    }
+
+    private Button backButton() {
+        Button button = new Button();
+        button.id = Constants.BACK_BUTTON_ID;
+        return button;
+    }
+}