Update

app/src/main/java/com/hippo/scene/SceneManager.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2015 Hippo Seven
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.hippo.scene;
+
+import android.os.Bundle;
+
+import com.hippo.util.Log;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.Stack;
+
+class SceneManager {
+
+    private static final String TAG = SceneManager.class.getSimpleName();
+
+    private Stack<Scene> mSceneStack = new Stack<>();
+    private StageActivity mStageActivity;
+
+    // Should only be called by SceneApplication
+    SceneManager() {
+    }
+
+    void setStageActivity(StageActivity stageActivity) {
+        mStageActivity = stageActivity;
+    }
+
+    StageActivity getStageActivity() {
+        return mStageActivity;
+    }
+
+    void startScene(@NotNull Class sceneClass, @Nullable Announcer announcer) {
+        Scene scene;
+        try {
+            scene = (Scene) sceneClass.newInstance();
+        } catch (InstantiationException e) {
+            throw new IllegalStateException("Can't instance " + sceneClass.getName());
+        } catch (IllegalAccessException e) {
+            throw new IllegalStateException("The constructor of " +
+                    sceneClass.getName() + " is not visible");
+        } catch (ClassCastException e) {
+            throw new IllegalStateException(sceneClass.getName() + " can not cast to scene");
+        }
+
+        Scene topScene = getTopState();
+        if (topScene != null) {
+            topScene.pause();
+        }
+
+        mSceneStack.push(scene);
+
+        scene.create(null);
+        scene.resume();
+    }
+
+    void finishScene(@NotNull Scene scene) {
+        if (mSceneStack.remove(scene)) {
+            scene.destroy();
+        } else {
+            Log.e(TAG, "The scene is not in stage");
+        }
+    }
+
+    boolean onBackPressed() {
+        Scene scene = getTopState();
+        if (scene != null) {
+            scene.onBackPressed();
+            return true;
+        } else {
+            Log.w(TAG, "There is no scene in the stage");
+            return false;
+        }
+    }
+
+    private Scene getTopState() {
+        if (!mSceneStack.isEmpty()) {
+            return mSceneStack.peek();
+        } else {
+            return null;
+        }
+    }
+
+    private Scene getSecondTopState() {
+        int secondTopIndex = mSceneStack.size() - 2;
+        if (secondTopIndex >= 0) {
+            return mSceneStack.get(secondTopIndex);
+        } else {
+            return null;
+        }
+    }
+
+    protected void onSaveInstanceState(Bundle outState) {
+        for (Scene scene : mSceneStack) {
+            scene.onSaveInstanceState(outState);
+        }
+    }
+
+    protected void onRestoreInstanceState(@NotNull Bundle savedInstanceState) {
+        for (Scene scene : mSceneStack) {
+            // Recreate
+            scene.create(savedInstanceState);
+            scene.resume();
+            scene.onRestoreInstanceState(savedInstanceState);
+        }
+    }
+}