From 0593aaa0c1ceb06c9139b4861b5b9aa6d4a5ad47 Mon Sep 17 00:00:00 2001
From: yausername <13ritvik@gmail.com>
Date: Wed, 2 Oct 2019 06:29:20 +0530
Subject: [PATCH] fix scroll jittering

---
 .../support/design/widget/FlingBehavior.java  | 158 +++++++-----------
 1 file changed, 61 insertions(+), 97 deletions(-)

diff --git a/app/src/main/java/android/support/design/widget/FlingBehavior.java b/app/src/main/java/android/support/design/widget/FlingBehavior.java
index 59eb08294..6e4754e11 100644
--- a/app/src/main/java/android/support/design/widget/FlingBehavior.java
+++ b/app/src/main/java/android/support/design/widget/FlingBehavior.java
@@ -1,116 +1,80 @@
 package android.support.design.widget;
 
-import android.animation.ValueAnimator;
 import android.content.Context;
-import android.support.annotation.NonNull;
-import android.support.design.animation.AnimationUtils;
+import android.support.annotation.Nullable;
 import android.util.AttributeSet;
-import android.view.View;
+import android.view.MotionEvent;
+import android.widget.OverScroller;
 
-// check this https://github.com/ToDou/appbarlayout-spring-behavior/blob/master/appbarspring/src/main/java/android/support/design/widget/AppBarFlingFixBehavior.java
+import java.lang.reflect.Field;
+
+// check this https://stackoverflow.com/questions/56849221/recyclerview-fling-causes-laggy-while-appbarlayout-is-scrolling/57997489#57997489
 public final class FlingBehavior extends AppBarLayout.Behavior {
 
-    private ValueAnimator mOffsetAnimator;
-    private static final int MAX_OFFSET_ANIMATION_DURATION = 600; // ms
-
-    public FlingBehavior() {
-    }
-
     public FlingBehavior(Context context, AttributeSet attrs) {
         super(context, attrs);
     }
 
     @Override
-    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy, int[] consumed, int type) {
-        if (dy != 0) {
-            int val = child.getBottom();
-            if (val != 0) {
-                int min, max;
-                if (dy < 0) {
-                    // We're scrolling down
-                } else {
-                    // We're scrolling up
-                    if (mOffsetAnimator != null && mOffsetAnimator.isRunning()) {
-                        mOffsetAnimator.cancel();
-                    }
-                    min = -child.getUpNestedPreScrollRange();
-                    max = 0;
-                    consumed[1] = scroll(coordinatorLayout, child, dy, min, max);
-                }
+    public boolean onInterceptTouchEvent(CoordinatorLayout parent, AppBarLayout child, MotionEvent ev) {
+        switch (ev.getActionMasked()) {
+            case MotionEvent.ACTION_DOWN:
+                // remove reference to old nested scrolling child
+                resetNestedScrollingChild();
+                // Stop fling when your finger touches the screen
+                stopAppBarLayoutFling();
+                break;
+            default:
+                break;
+        }
+        return super.onInterceptTouchEvent(parent, child, ev);
+    }
+
+    @Nullable
+    private OverScroller getScrollerField() {
+        try {
+            Class<?> headerBehaviorType = this.getClass().getSuperclass().getSuperclass().getSuperclass();
+            if (headerBehaviorType != null) {
+                Field field = headerBehaviorType.getDeclaredField("scroller");
+                field.setAccessible(true);
+                return ((OverScroller) field.get(this));
+            }
+        } catch (NoSuchFieldException | IllegalAccessException e) {
+            // ?
+        }
+        return null;
+    }
+
+    @Nullable
+    private Field getLastNestedScrollingChildRefField() {
+        try {
+            Class<?> headerBehaviorType = this.getClass().getSuperclass().getSuperclass();
+            if (headerBehaviorType != null) {
+                Field field = headerBehaviorType.getDeclaredField("lastNestedScrollingChildRef");
+                field.setAccessible(true);
+                return field;
+            }
+        } catch (NoSuchFieldException e) {
+            // ?
+        }
+        return null;
+    }
+
+    private void resetNestedScrollingChild(){
+        Field field = getLastNestedScrollingChildRefField();
+        if(field != null){
+            try {
+                Object value = field.get(this);
+                if(value != null) field.set(this, null);
+            } catch (IllegalAccessException e) {
+                // ?
             }
         }
     }
 
-    @Override
-    public boolean onNestedPreFling(@NonNull CoordinatorLayout coordinatorLayout, @NonNull AppBarLayout child, @NonNull View target, float velocityX, float velocityY) {
-
-        if (velocityY != 0) {
-            if (velocityY < 0) {
-                // We're flinging down
-                int val = child.getBottom();
-                if (val != 0) {
-                    final int targetScroll =
-                            +child.getDownNestedPreScrollRange();
-                    animateOffsetTo(coordinatorLayout, child, targetScroll, velocityY);
-                }
-
-            } else {
-                // We're flinging up
-                int val = child.getBottom();
-                if (val != 0) {
-                    final int targetScroll = -child.getUpNestedPreScrollRange();
-                    if (getTopBottomOffsetForScrollingSibling() > targetScroll) {
-                        animateOffsetTo(coordinatorLayout, child, targetScroll, velocityY);
-                    }
-                }
-            }
-        }
-
-        return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
+    private void stopAppBarLayoutFling() {
+        OverScroller scroller = getScrollerField();
+        if (scroller != null) scroller.forceFinished(true);
     }
 
-    private void animateOffsetTo(final CoordinatorLayout coordinatorLayout,
-                                 final AppBarLayout child, final int offset, float velocity) {
-        final int distance = Math.abs(getTopBottomOffsetForScrollingSibling() - offset);
-
-        final int duration;
-        velocity = Math.abs(velocity);
-        if (velocity > 0) {
-            duration = 3 * Math.round(1000 * (distance / velocity));
-        } else {
-            final float distanceRatio = (float) distance / child.getHeight();
-            duration = (int) ((distanceRatio + 1) * 150);
-        }
-
-        animateOffsetWithDuration(coordinatorLayout, child, offset, duration);
-    }
-
-    private void animateOffsetWithDuration(final CoordinatorLayout coordinatorLayout,
-                                           final AppBarLayout child, final int offset, final int duration) {
-        final int currentOffset = getTopBottomOffsetForScrollingSibling();
-        if (currentOffset == offset) {
-            if (mOffsetAnimator != null && mOffsetAnimator.isRunning()) {
-                mOffsetAnimator.cancel();
-            }
-            return;
-        }
-
-        if (mOffsetAnimator == null) {
-            mOffsetAnimator = new ValueAnimator();
-            mOffsetAnimator.setInterpolator(AnimationUtils.DECELERATE_INTERPOLATOR);
-            mOffsetAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
-                @Override
-                public void onAnimationUpdate(ValueAnimator animator) {
-                    setHeaderTopBottomOffset(coordinatorLayout, child,
-                            (Integer) animator.getAnimatedValue());
-                }
-            });
-        } else {
-            mOffsetAnimator.cancel();
-        }
-
-        mOffsetAnimator.setDuration(Math.min(duration, MAX_OFFSET_ANIMATION_DURATION));
-        mOffsetAnimator.setIntValues(currentOffset, offset);
-        mOffsetAnimator.start();
-    }
 }
\ No newline at end of file