Update

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

@@ -21,9 +21,13 @@ import android.os.Parcelable;
 import android.support.v4.app.FragmentManager;
 import android.util.SparseArray;
 import android.view.View;
-import android.widget.FrameLayout;
+import android.view.ViewParent;
 
 import com.hippo.util.AssertUtils;
+import com.hippo.util.Log;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 /**
  * {@link com.hippo.scene.Scene} is a {@code Activity} of {@link android.app.Activity}.
@@ -33,60 +37,43 @@ import com.hippo.util.AssertUtils;
  */
 public abstract class Scene {
 
-    private StageActivity mStageActivity;
-    private FrameLayout mStageView;
-    private View mRootView;
+    private @Nullable View mSceneView;
 
-    void setStageActivity(StageActivity stageActivity) {
-        mStageActivity = stageActivity;
-        mStageView = stageActivity.getStageView();
-    }
+    private static SceneManager sSceneManager;
 
-    public void setContentView(int layoutResID) {
-        mRootView = mStageActivity.getLayoutInflater()
-                .inflate(layoutResID, mStageView, false);
-    }
-
-    public void setContentView(View view) {
-        mRootView = view;
-    }
-
-    public View findViewById(int id) {
-        AssertUtils.assertNotNull("Call setContentView before findViewById",
-                mRootView);
-
-        return mRootView.findViewById(id);
-    }
-
-    View getRootView() {
-        return mRootView;
+    static void setSceneManager(SceneManager sceneManager) {
+        sSceneManager = sceneManager;
     }
 
+    // If there is no StageActivity for SceneManager, yout will get AssertError
     public StageActivity getStageActivity() {
-        return mStageActivity;
+        StageActivity stageActivity = sSceneManager.getStageActivity();
+        AssertUtils.assertNotNull("StageActivity is null", stageActivity);
+        return stageActivity;
     }
 
-    public void startScene(Class sceneClass) {
-        mStageActivity.startScene(this, sceneClass);
+    View getSceneView() {
+        return mSceneView;
+    }
+
+    public void startScene(@NotNull Class sceneClass, @Nullable Announcer announcer) {
+        sSceneManager.startScene(sceneClass, announcer);
     }
 
     public final void finish() {
-        mStageActivity.finishScene(this);
+        sSceneManager.finishScene(this);
     }
 
-    void create() {
-        onCreate();
+    void create(Bundle savedInstanceState) {
+        onCreate(savedInstanceState);
+        mSceneView = onCreateSceneView(savedInstanceState);
 
-        AssertUtils.assertNotNull("You have to call setContentView in onCreate",
-                mRootView);
-
-        mStageActivity.addSceneView(this);
+        // Make sure scene view is attach from stage
+        attachToStage();
     }
 
     void resume() {
         onResume();
-
-        mStageActivity.addSceneView(this);
     }
 
     void pause() {
@@ -95,46 +82,118 @@ public abstract class Scene {
 
     void destroy() {
         onDestroy();
+
+        // Make sure scene view is detached from stage
+        detachFromeStage();
     }
 
     /**
-     * You have to call setContentView in it.
+     * It is called when scene is created
+     *
+     * @param savedInstanceState null for first time, non null for recrearte
      */
-    public abstract void onCreate();
-
-    public abstract void onResume();
-
-    public abstract void onPause();
-
-    public abstract void onDestroy();
+    protected void onCreate(Bundle savedInstanceState) {
+    }
 
     /**
-     * This method should be called to remove when it need to remove
+     * It is called after {@link #onCreate(android.os.Bundle)}.
+     * Create view of the scene.
+     *
+     * @param savedInstanceState null for first time, non null for recrearte
+     * @return the view of the scene
      */
-    public final void dispatchRemove() {
-        mStageActivity.stopSceneRetain(this);
+    protected @Nullable View onCreateSceneView(Bundle savedInstanceState) {
+        return null;
+    }
+
+    protected void onResume() {
+    }
+
+    protected void onPause() {
+    }
+
+    protected void onDestroy() {
+    }
+
+
+    /**
+     * Is scene view attached to stage
+     *
+     * @return if scene view is null, always return false;
+     */
+    public boolean isInStage() {
+        if (mSceneView == null) {
+            return false;
+        } else {
+            ViewParent parent = mSceneView.getParent();
+
+            if (parent == null) {
+                return false;
+            } else if (parent == getStageActivity().getStageLayout()) {
+                return true;
+            } else {
+                throw new IllegalStateException("Scene view should only be the child of stage layout");
+            }
+        }
+    }
+
+    // Add scene view to stage layout
+    void attachToStage() {
+        if (mSceneView != null && !isInStage()) {
+
+            Log.d("doAttachToStage();");
+            doAttachToStage();
+        }
+    }
+
+    void attachToStageAsPreScene() {
+        // TODO
+    }
+
+    // Remove scene view from stage layout
+    void detachFromeStage() {
+        if (mSceneView != null && isInStage()) {
+            doDetachFromeStage();
+        }
+    }
+
+    void doAttachToStage() {
+        getStageActivity().attachSceneToStage(this);
+    }
+
+    void doAttachToStageAsPreScene() {
+        getStageActivity().attachSceneToStageAsPreScene(this);
+    }
+
+    void doDetachFromeStage() {
+        getStageActivity().detachSceneFromStage(this);
     }
 
     public void onBackPressed() {
         finish();
     }
 
-    protected void onSaveInstanceState(Bundle outState) {
-        SparseArray<Parcelable> states = new SparseArray<>();
-        mRootView.saveHierarchyState(states);
-        outState.putSparseParcelableArray(Integer.toHexString(hashCode()), states);
+    // It is constant
+    private String getStateKey() {
+        return "scene:" + Integer.toHexString(hashCode());
     }
 
-    protected void onRestoreInstanceState(Bundle savedInstanceState) {
+    protected void onSaveInstanceState(Bundle outState) {
+        SparseArray<Parcelable> states = new SparseArray<>();
+        mSceneView.saveHierarchyState(states);
+        outState.putSparseParcelableArray(getStateKey(), states);
+    }
+
+    protected void onRestoreInstanceState(@NotNull Bundle savedInstanceState) {
         SparseArray<Parcelable> savedStates
-                = savedInstanceState.getSparseParcelableArray(Integer.toHexString(hashCode()));
+                = savedInstanceState.getSparseParcelableArray(getStateKey());
         if (savedStates != null) {
-            mRootView.restoreHierarchyState(savedStates);
+            mSceneView.restoreHierarchyState(savedStates);
         }
     }
 
     public void startActivityForResult(Intent intent, ActivityResultListener listener) {
-        mStageActivity.startActivityForResult(intent, listener);
+        getStageActivity().startActivityForResult(intent, listener);
     }
 
     /**
@@ -142,7 +201,7 @@ public abstract class Scene {
      * with StageActivity.
      */
     public FragmentManager getSupportFragmentManager() {
-        return mStageActivity.getSupportFragmentManager();
+        return getStageActivity().getSupportFragmentManager();
     }
 
     public interface ActivityResultListener {