Destroy fragment's presenter when they aren't needed using FragmentStack class from Nucleus' examples

app/src/main/java/eu/kanade/mangafeed/ui/main/FragmentStack.java

@@ -0,0 +1,179 @@
+package eu.kanade.mangafeed.ui.main;
+
+import android.app.Activity;
+import android.support.annotation.Nullable;
+import android.support.v4.app.Fragment;
+import android.support.v4.app.FragmentManager;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import eu.kanade.mangafeed.R;
+
+/**
+ * Why this class is needed.
+ *
+ * FragmentManager does not supply a developer with a fragment stack.
+ * It gives us a fragment *transaction* stack.
+ *
+ * To be sane, we need *fragment* stack.
+ *
+ * This implementation also handles NucleusSupportFragment presenter`s lifecycle correctly.
+ */
+public class FragmentStack {
+
+    public interface OnBackPressedHandlingFragment {
+        boolean onBackPressed();
+    }
+
+    public interface OnFragmentRemovedListener {
+        void onFragmentRemoved(Fragment fragment);
+    }
+
+    private Activity activity;
+    private FragmentManager manager;
+    private int containerId;
+    @Nullable private OnFragmentRemovedListener onFragmentRemovedListener;
+
+    public FragmentStack(Activity activity, FragmentManager manager, int containerId, @Nullable OnFragmentRemovedListener onFragmentRemovedListener) {
+        this.activity = activity;
+        this.manager = manager;
+        this.containerId = containerId;
+        this.onFragmentRemovedListener = onFragmentRemovedListener;
+    }
+
+    /**
+     * Returns the number of fragments in the stack.
+     *
+     * @return the number of fragments in the stack.
+     */
+    public int size() {
+        return getFragments().size();
+    }
+
+    /**
+     * Pushes a fragment to the top of the stack.
+     */
+    public void push(Fragment fragment) {
+
+        Fragment top = peek();
+        if (top != null) {
+            manager.beginTransaction()
+                    .setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left, R.anim.enter_from_left, R.anim.exit_to_right)
+                    .remove(top)
+                    .add(containerId, fragment, indexToTag(manager.getBackStackEntryCount() + 1))
+                    .addToBackStack(null)
+                    .commit();
+        }
+        else {
+            manager.beginTransaction()
+                    .add(containerId, fragment, indexToTag(0))
+                    .commit();
+        }
+
+        manager.executePendingTransactions();
+    }
+
+    /**
+     * Pops the top item if the stack.
+     * If the fragment implements {@link OnBackPressedHandlingFragment}, calls {@link OnBackPressedHandlingFragment#onBackPressed()} instead.
+     * If {@link OnBackPressedHandlingFragment#onBackPressed()} returns false the fragment gets popped.
+     *
+     * @return true if a fragment has been popped or if {@link OnBackPressedHandlingFragment#onBackPressed()} returned true;
+     */
+    public boolean back() {
+        Fragment top = peek();
+        if (top instanceof OnBackPressedHandlingFragment) {
+            if (((OnBackPressedHandlingFragment)top).onBackPressed())
+                return true;
+        }
+        return pop();
+    }
+
+    /**
+     * Pops the topmost fragment from the stack.
+     * The lowest fragment can't be popped, it can only be replaced.
+     *
+     * @return false if the stack can't pop or true if a top fragment has been popped.
+     */
+    public boolean pop() {
+        if (manager.getBackStackEntryCount() == 0)
+            return false;
+        Fragment top = peek();
+        manager.popBackStackImmediate();
+        if (onFragmentRemovedListener != null)
+            onFragmentRemovedListener.onFragmentRemoved(top);
+        return true;
+    }
+
+    /**
+     * Replaces stack contents with just one fragment.
+     */
+    public void replace(Fragment fragment) {
+        List<Fragment> fragments = getFragments();
+
+        manager.popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
+        manager.beginTransaction()
+                .replace(containerId, fragment, indexToTag(0))
+                .commit();
+        manager.executePendingTransactions();
+
+        if (onFragmentRemovedListener != null) {
+            for (Fragment fragment1 : fragments)
+                onFragmentRemovedListener.onFragmentRemoved(fragment1);
+        }
+    }
+
+    /**
+     * Returns the topmost fragment in the stack.
+     */
+    public Fragment peek() {
+        return manager.findFragmentById(containerId);
+    }
+
+    /**
+     * Returns a back fragment if the fragment is of given class.
+     * If such fragment does not exist and activity implements the given class then the activity will be returned.
+     *
+     * @param fragment     a fragment to search from.
+     * @param callbackType a class of type for callback to search.
+     * @param <T>          a type of callback.
+     * @return a back fragment or activity.
+     */
+    @SuppressWarnings("unchecked")
+    public <T> T findCallback(Fragment fragment, Class<T> callbackType) {
+
+        Fragment back = getBackFragment(fragment);
+
+        if (back != null && callbackType.isAssignableFrom(back.getClass()))
+            return (T)back;
+
+        if (callbackType.isAssignableFrom(activity.getClass()))
+            return (T)activity;
+
+        return null;
+    }
+
+    private Fragment getBackFragment(Fragment fragment) {
+        List<Fragment> fragments = getFragments();
+        for (int f = fragments.size() - 1; f >= 0; f--) {
+            if (fragments.get(f) == fragment && f > 0)
+                return fragments.get(f - 1);
+        }
+        return null;
+    }
+
+    private List<Fragment> getFragments() {
+        List<Fragment> fragments = new ArrayList<>(manager.getBackStackEntryCount() + 1);
+        for (int i = 0; i < manager.getBackStackEntryCount() + 1; i++) {
+            Fragment fragment = manager.findFragmentByTag(indexToTag(i));
+            if (fragment != null)
+                fragments.add(fragment);
+        }
+        return fragments;
+    }
+
+    private String indexToTag(int index) {
+        return Integer.toString(index);
+    }
+}

app/src/main/java/eu/kanade/mangafeed/ui/main/MainActivity.java

@@ -3,7 +3,6 @@ package eu.kanade.mangafeed.ui.main;
 import android.content.Intent;
 import android.os.Bundle;
 import android.support.v4.app.Fragment;
-import android.support.v4.app.FragmentTransaction;
 import android.support.v7.widget.Toolbar;
 import android.widget.FrameLayout;
 
@@ -19,6 +18,7 @@ import eu.kanade.mangafeed.ui.catalogue.SourceFragment;
 import eu.kanade.mangafeed.ui.download.DownloadFragment;
 import eu.kanade.mangafeed.ui.library.LibraryFragment;
 import eu.kanade.mangafeed.ui.setting.SettingsActivity;
+import nucleus.view.ViewWithPresenter;
 
 public class MainActivity extends BaseActivity {
 
@@ -29,6 +29,7 @@ public class MainActivity extends BaseActivity {
     FrameLayout container;
 
     private Drawer drawer;
+    private FragmentStack fragmentStack;
 
     private final static String SELECTED_ITEM = "selected_item";
 
@@ -40,6 +41,12 @@ public class MainActivity extends BaseActivity {
 
         setupToolbar(toolbar);
 
+        fragmentStack = new FragmentStack(this, getSupportFragmentManager(), R.id.content_layout,
+                fragment -> {
+                    if (fragment instanceof ViewWithPresenter)
+                        ((ViewWithPresenter)fragment).getPresenter().destroy();
+                });
+
         drawer = new DrawerBuilder()
                 .withActivity(this)
                 .withRootView(container)
@@ -103,17 +110,7 @@ public class MainActivity extends BaseActivity {
     }
 
     public void setFragment(Fragment fragment) {
-        try {
-            if (fragment != null && getSupportFragmentManager() != null) {
-                FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
-                if (ft != null) {
-                    ft.replace(R.id.content_layout, fragment);
-                    ft.commit();
-                }
-            }
-        } catch (Exception e) {
-
-        }
+        fragmentStack.replace(fragment);
     }
 
 }

app/src/main/res/anim/enter_from_left.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<set xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shareInterpolator="false">
+    <translate
+        android:duration="400"
+        android:fromXDelta="-100%"
+        android:toXDelta="0%" />
+</set>

app/src/main/res/anim/enter_from_right.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<set xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shareInterpolator="false">
+    <translate
+        android:duration="400"
+        android:fromXDelta="100%"
+        android:toXDelta="0%" />
+</set>

app/src/main/res/anim/exit_to_left.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<set xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shareInterpolator="false">
+    <translate
+        android:duration="400"
+        android:fromXDelta="0%"
+        android:toXDelta="-100%" />
+</set>

app/src/main/res/anim/exit_to_right.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<set xmlns:android="http://schemas.android.com/apk/res/android"
+    android:shareInterpolator="false">
+    <translate
+        android:duration="400"
+        android:fromXDelta="0%"
+        android:toXDelta="100%" />
+</set>