Do trick to draw disappearing children first

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

@@ -19,8 +19,12 @@ package com.hippo.scene;
 import android.os.Bundle;
 import android.support.annotation.IntDef;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentActivity;
+import android.view.View;
+
+import com.hippo.ehviewer.R;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
@@ -97,4 +101,12 @@ public class SceneFragment extends Fragment {
     public boolean onBackPressed() {
         return false;
     }
+
+    @Override
+    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
+        super.onViewCreated(view, savedInstanceState);
+
+        view.setTag(R.id.fragment_tag, getTag());
+        view.setBackgroundColor(getContext().getResources().getColor(R.color.background_light));
+    }
 }

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

@@ -28,7 +28,6 @@ import com.hippo.ehviewer.R;
 import com.hippo.yorozuya.IntIdGenerator;
 
 import java.util.ArrayList;
-import java.util.Collections;
 
 public abstract class StageActivity extends AppCompatActivity {
 
@@ -148,7 +147,14 @@ public abstract class StageActivity extends AppCompatActivity {
     }
 
     int getStackIndex(String tag) {
-        return Collections.binarySearch(mSceneTagList, tag);
+        return mSceneTagList.indexOf(tag); // Collections.binarySearch(mSceneTagList, tag);
+    }
+
+    // TODO What about id is negative
+    int compareScene(String tag1, String tag2) throws NumberFormatException {
+        int int1 = Integer.parseInt(tag1);
+        int int2 = Integer.parseInt(tag2);
+        return int1 - int2;
     }
 
     public void finishScene(SceneFragment scene) {

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

@@ -0,0 +1,143 @@
+/*
+ * Copyright 2016 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
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * 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.content.Context;
+import android.graphics.Canvas;
+import android.util.AttributeSet;
+import android.view.View;
+import android.view.ViewGroup;
+import android.widget.FrameLayout;
+
+import com.hippo.ehviewer.R;
+
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+
+public class StageLayout extends FrameLayout {
+
+    private Field mDisappearingChildrenField;
+    private ArrayList<View> mSuperDisappearingChildren;
+    private View mDumpView;
+    private boolean mDoTrick;
+
+    public StageLayout(Context context) {
+        super(context);
+        init(context);
+    }
+
+    public StageLayout(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        init(context);
+    }
+
+    public StageLayout(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+        init(context);
+    }
+
+    private void init(Context context) {
+        try {
+            mDisappearingChildrenField = ViewGroup.class.getDeclaredField("mDisappearingChildren");
+            mDisappearingChildrenField.setAccessible(true);
+        } catch (NoSuchFieldException e) {
+            e.printStackTrace();
+        }
+
+        if (mDisappearingChildrenField != null) {
+            mDumpView = new View(context);
+            addView(mDumpView, LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
+        }
+    }
+
+    @SuppressWarnings("unchecked")
+    private void getSuperDisappearingChildren() {
+        if (mDisappearingChildrenField == null || mSuperDisappearingChildren != null) {
+            return;
+        }
+
+        try {
+            mSuperDisappearingChildren = (ArrayList<View>) mDisappearingChildrenField.get(this);
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+
+    private String getViewTag(View view) {
+        Object tag = view.getTag(R.id.fragment_tag);
+        if (tag instanceof String) {
+            return (String) tag;
+        } else {
+            return null;
+        }
+    }
+
+    private boolean beforeDispatchDraw() {
+        getSuperDisappearingChildren();
+
+        if (mSuperDisappearingChildren == null ||
+                mSuperDisappearingChildren.size() <= 0 || getChildCount() <= 1) { // dump view
+            return false;
+        }
+
+        StageActivity stage = null;
+        Context context = getContext();
+        if (context instanceof StageActivity) {
+            stage = (StageActivity) context;
+        }
+        if (stage == null) {
+            return false;
+        }
+
+        View view1 = mSuperDisappearingChildren.get(0);
+        View view2 = getChildAt(1); // dump view
+        String tag1 = getViewTag(view1);
+        String tag2 = getViewTag(view2);
+        try {
+            return stage.compareScene(tag1, tag2) < 0;
+        } catch (NumberFormatException e) {
+            return false;
+        }
+    }
+
+    @Override
+    protected void dispatchDraw(Canvas canvas) {
+        mDoTrick = beforeDispatchDraw();
+        super.dispatchDraw(canvas);
+        mDoTrick = false;
+    }
+
+    @Override
+    protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
+        ArrayList<View> disappearingChildren = mSuperDisappearingChildren;
+
+        if (mDoTrick && disappearingChildren != null && disappearingChildren.size() > 0) {
+            if (child == mDumpView) {
+                boolean more = false;
+                for (int i = disappearingChildren.size() - 1; i >= 0; i--) {
+                    more |= super.drawChild(canvas, disappearingChildren.get(i), drawingTime);
+                }
+                return more;
+            } else if (disappearingChildren.contains(child)) {
+                // Skip
+                return false;
+            }
+        }
+
+        return super.drawChild(canvas, child, drawingTime);
+    }
+}