xplat/js/react-native-github/packages/react-native/ReactAndroid/src/m…

…ain/java/com/facebook/react/views/scroll/OnScrollDispatchHelper.java (#45676)

Summary:
Pull Request resolved: #45676

Changelog: [Internal]

Reviewed By: christophpurrer

Differential Revision: D60233460

fbshipit-source-id: 7524fe461846466118e7037f01ac828535533d17

packages/react-native/ReactAndroid/api/ReactAndroid.api

@@ -6646,11 +6646,11 @@ public abstract interface class com/facebook/react/views/scroll/FpsListener {
 	public abstract fun isEnabled ()Z
 }
 
-public class com/facebook/react/views/scroll/OnScrollDispatchHelper {
+public final class com/facebook/react/views/scroll/OnScrollDispatchHelper {
 	public fun <init> ()V
-	public fun getXFlingVelocity ()F
-	public fun getYFlingVelocity ()F
-	public fun onScrollChanged (II)Z
+	public final fun getXFlingVelocity ()F
+	public final fun getYFlingVelocity ()F
+	public final fun onScrollChanged (II)Z
 }
 
 public class com/facebook/react/views/scroll/ReactHorizontalScrollContainerView : com/facebook/react/views/view/ReactViewGroup {

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/OnScrollDispatchHelper.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.scroll
+
+import android.os.SystemClock
+
+/**
+ * Android has a bug where onScrollChanged is called twice per frame with the same params during
+ * flings. We hack around that here by trying to detect that duplicate call and not dispatch it. See
+ * https://code.google.com/p/android/issues/detail?id=39473
+ */
+public class OnScrollDispatchHelper {
+
+  private var prevX = Int.MIN_VALUE
+  private var prevY = Int.MIN_VALUE
+  public var xFlingVelocity: Float = 0f
+    private set
+
+  public var yFlingVelocity: Float = 0f
+    private set
+
+  private var lastScrollEventTimeMs = -(MIN_EVENT_SEPARATION_MS + 1).toLong()
+
+  /**
+   * Call from a ScrollView in onScrollChanged, returns true if this onScrollChanged is legit (not a
+   * duplicate) and should be dispatched.
+   */
+  public fun onScrollChanged(x: Int, y: Int): Boolean {
+    val eventTime = SystemClock.uptimeMillis()
+    val shouldDispatch =
+        eventTime - lastScrollEventTimeMs > MIN_EVENT_SEPARATION_MS || prevX != x || prevY != y
+    if (eventTime - lastScrollEventTimeMs != 0L) {
+      xFlingVelocity = (x - prevX).toFloat() / (eventTime - lastScrollEventTimeMs)
+      yFlingVelocity = (y - prevY).toFloat() / (eventTime - lastScrollEventTimeMs)
+    }
+    lastScrollEventTimeMs = eventTime
+    prevX = x
+    prevY = y
+    return shouldDispatch
+  }
+
+  private companion object {
+    private const val MIN_EVENT_SEPARATION_MS = 10
+  }
+}