From 03d7c7a6a1257d15c26e61cd660fb57222b5b969 Mon Sep 17 00:00:00 2001
From: Krzysztof Magiera <krzysztof@fb.com>
Date: Wed, 28 Oct 2015 14:24:18 -0700
Subject: [PATCH] Recycle scroll events.

Reviewed By: mkonicek

Differential Revision: D2591945

fb-gh-sync-id: 1c9bfdc88ef5add38fcf0c9499bf52a8a940a22e
---
 .../RecyclerViewBackedScrollView.java         | 19 +++----
 .../views/scroll/ReactScrollViewHelper.java   |  2 +-
 .../react/views/scroll/ScrollEvent.java       | 56 ++++++++++++++++---
 3 files changed, 58 insertions(+), 19 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/recyclerview/RecyclerViewBackedScrollView.java b/ReactAndroid/src/main/java/com/facebook/react/views/recyclerview/RecyclerViewBackedScrollView.java
index 5b191eca2..118cb50d1 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/recyclerview/RecyclerViewBackedScrollView.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/recyclerview/RecyclerViewBackedScrollView.java
@@ -247,17 +247,16 @@ public class RecyclerViewBackedScrollView extends RecyclerView {
   protected void onScrollChanged(int l, int t, int oldl, int oldt) {
     super.onScrollChanged(l, t, oldl, oldt);
 
-    ScrollEvent event = new ScrollEvent(
-        getId(),
-        SystemClock.uptimeMillis(),
-        0, /* offsetX = 0, horizontal scrolling only */
-        calculateAbsoluteOffset(),
-        getWidth(),
-        ((ReactListAdapter) getAdapter()).getTotalChildrenHeight(),
-        getWidth(),
-        getHeight());
     ((ReactContext) getContext()).getNativeModule(UIManagerModule.class).getEventDispatcher()
-        .dispatchEvent(event);
+        .dispatchEvent(ScrollEvent.obtain(
+                getId(),
+                SystemClock.uptimeMillis(),
+                0, /* offsetX = 0, horizontal scrolling only */
+                calculateAbsoluteOffset(),
+                getWidth(),
+                ((ReactListAdapter) getAdapter()).getTotalChildrenHeight(),
+                getWidth(),
+                getHeight()));
   }
 
   public RecyclerViewBackedScrollView(Context context) {
diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
index c0b72def6..12f5606fc 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
@@ -28,7 +28,7 @@ public class ReactScrollViewHelper {
     View contentView = scrollView.getChildAt(0);
     ReactContext reactContext = (ReactContext) scrollView.getContext();
     reactContext.getNativeModule(UIManagerModule.class).getEventDispatcher().dispatchEvent(
-        new ScrollEvent(
+        ScrollEvent.obtain(
             scrollView.getId(),
             SystemClock.uptimeMillis(),
             scrollX,
diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.java
index 6d9220037..fdf8cd5a2 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ScrollEvent.java
@@ -9,6 +9,10 @@
 
 package com.facebook.react.views.scroll;
 
+import java.lang.Override;
+
+import android.support.v4.util.Pools;
+
 import com.facebook.react.bridge.Arguments;
 import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.uimanager.PixelUtil;
@@ -20,16 +24,19 @@ import com.facebook.react.uimanager.events.RCTEventEmitter;
  */
 public class ScrollEvent extends Event<ScrollEvent> {
 
+  private static final Pools.SynchronizedPool<ScrollEvent> EVENTS_POOL =
+      new Pools.SynchronizedPool<>(3);
+
   public static final String EVENT_NAME = "topScroll";
 
-  private final int mScrollX;
-  private final int mScrollY;
-  private final int mContentWidth;
-  private final int mContentHeight;
-  private final int mScrollViewWidth;
-  private final int mScrollViewHeight;
+  private int mScrollX;
+  private int mScrollY;
+  private int mContentWidth;
+  private int mContentHeight;
+  private int mScrollViewWidth;
+  private int mScrollViewHeight;
 
-  public ScrollEvent(
+  public static ScrollEvent obtain(
       int viewTag,
       long timestampMs,
       int scrollX,
@@ -38,7 +45,40 @@ public class ScrollEvent extends Event<ScrollEvent> {
       int contentHeight,
       int scrollViewWidth,
       int scrollViewHeight) {
-    super(viewTag, timestampMs);
+    ScrollEvent event = EVENTS_POOL.acquire();
+    if (event == null) {
+      event = new ScrollEvent();
+    }
+    event.init(
+        viewTag,
+        timestampMs,
+        scrollX,
+        scrollY,
+        contentWidth,
+        contentHeight,
+        scrollViewWidth,
+        scrollViewHeight);
+    return event;
+  }
+
+  @Override
+  public void onDispose() {
+    EVENTS_POOL.release(this);
+  }
+
+  private ScrollEvent() {
+  }
+
+  private void init(
+      int viewTag,
+      long timestampMs,
+      int scrollX,
+      int scrollY,
+      int contentWidth,
+      int contentHeight,
+      int scrollViewWidth,
+      int scrollViewHeight) {
+    super.init(viewTag, timestampMs);
     mScrollX = scrollX;
     mScrollY = scrollY;
     mContentWidth = contentWidth;