From d568294c1a587fd712b41f072d6e1a521fe09a72 Mon Sep 17 00:00:00 2001
From: Matt Pietal <mpietal@google.com>
Date: Mon, 8 Apr 2019 09:57:07 -0400
Subject: [PATCH] Sharesheet - Fix scroll behavior moving past bounds

ResolverDrawerLayout is tracking fractions of pixels, but just drops
these fractions when offsetting the child views. When scrolling up and
down continuously, this can lead to the view scrolling past the window
bounds. Do not discard these fractions. Track the remainders and add
them in when the sum to >= 1px.

Bug: 129979914
Test: Manual scrolling test
Change-Id: I0e8ea04baca341c6b6e0573e086f3f2f8c2b39b5
---
 .../internal/widget/ResolverDrawerLayout.java     | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/core/java/com/android/internal/widget/ResolverDrawerLayout.java b/core/java/com/android/internal/widget/ResolverDrawerLayout.java
index 329c6b395bba..66bbe22c9969 100644
--- a/core/java/com/android/internal/widget/ResolverDrawerLayout.java
+++ b/core/java/com/android/internal/widget/ResolverDrawerLayout.java
@@ -73,6 +73,11 @@ public class ResolverDrawerLayout extends ViewGroup {
      */
     private float mCollapseOffset;
 
+    /**
+      * Track fractions of pixels from drag calculations. Without this, the view offsets get
+      * out of sync due to frequently dropping fractions of a pixel from '(int) dy' casts.
+      */
+    private float mDragRemainder = 0.0f;
     private int mCollapsibleHeight;
     private int mUncollapsibleHeight;
     private int mAlwaysShowHeight;
@@ -485,6 +490,16 @@ public class ResolverDrawerLayout extends ViewGroup {
                 mCollapsibleHeight + mUncollapsibleHeight));
         if (newPos != mCollapseOffset) {
             dy = newPos - mCollapseOffset;
+
+            mDragRemainder += dy - (int) dy;
+            if (mDragRemainder >= 1.0f) {
+                mDragRemainder -= 1.0f;
+                dy += 1.0f;
+            } else if (mDragRemainder <= -1.0f) {
+                mDragRemainder += 1.0f;
+                dy -= 1.0f;
+            }
+
             final int childCount = getChildCount();
             for (int i = 0; i < childCount; i++) {
                 final View child = getChildAt(i);