Refactor FlatViewGroup to use DrawCommandManagers.

Summary: Rework FlatViewGroup to more easily transition into more complex draw command managers.

Reviewed By: ahmedre

Differential Revision: D3536262

ReactAndroid/src/main/java/com/facebook/react/flat/DrawCommandManager.java

@@ -0,0 +1,93 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.flat;
+
+import java.util.Collection;
+
+import android.graphics.Canvas;
+import android.graphics.Rect;
+import android.view.View;
+import android.view.ViewParent;
+
+/**
+ * Underlying logic behind handling draw commands from {@link FlatViewGroup}.
+ */
+/* package */ abstract class DrawCommandManager {
+
+  /**
+   * Mount a set of draw commands to this manager.  The order the commands are given is the order in
+   * which they should be drawn.  If any of the commands are new DrawViews, then mountViews will be
+   * called after by the UIManager.
+   *
+   * @param drawCommands The draw commands to mount.
+   */
+  abstract void mountDrawCommands(DrawCommand[] drawCommands);
+
+  /**
+   * Add and detach a set of views.  The views added here will already have a DrawView passed in
+   * mountDrawCommands.
+   *
+   * @param viewResolver
+   * @param viewsToAdd The views to add, by tag.  If this is a new view, this will be reactTag,
+   *     otherwise it will be -reactTag.  This allows to optimize when we have already attached
+   *     views.
+   * @param viewsToDetach The views to detach, by tag.  These will all be positive.
+   */
+  abstract void mountViews(ViewResolver viewResolver, int[] viewsToAdd, int[] viewsToDetach);
+
+  /**
+   * Get the current clipping rect and adjust clipping so that when draw is dispatched we do as
+   * little work as possible.
+   *
+   * @return true if the FlatViewGroup should invalidate.
+   */
+  abstract boolean updateClippingRect();
+
+  /**
+   * Sets an input rect to match the bounds of our current clipping rect.
+   *
+   * @param outClippingRect Set the out
+   */
+  abstract void getClippingRect(Rect outClippingRect);
+
+  /**
+   * Return the views that are currently detached, so they can be cleaned up when we are.
+   *
+   * @return A collection of the currently detached views.
+   */
+  abstract Collection<View> getDetachedViews();
+
+  /**
+   * Draw the relevant items.  This should do as little work as possible.
+   *
+   * @param canvas The canvas to draw on.
+   */
+  abstract void draw(Canvas canvas);
+
+  /**
+   * Draws layout bounds for debug.
+   *
+   * @param canvas The canvas to draw on.
+   */
+  abstract void debugDraw(Canvas canvas);
+
+  /**
+   * Throw a runtime exception if a view we are trying to attach is already parented.
+   *
+   * @param view The view to check.
+   */
+  protected static void ensureViewHasNoParent(View view) {
+    ViewParent oldParent = view.getParent();
+    if (oldParent != null) {
+      throw new RuntimeException(
+          "Cannot add view " + view + " to DrawCommandManager while it has a parent " + oldParent);
+    }
+  }
+}