From 928cc599c2ab9cd94bb90de91f082277307528af Mon Sep 17 00:00:00 2001
From: Chris Banes <chrisbanes@google.com>
Date: Wed, 30 Nov 2016 01:31:50 +0000
Subject: [PATCH] am b27dc24f: am ec2310cd: Merge "Add ability to snap
 AppBarLayout children to edges" into mnc-ub-dev

* commit 'b27dc24f1e66228c02e96ce9014f6b1ef7e024c8':
  Add ability to snap AppBarLayout children to edges

GitOrigin-RevId=ab7326eb4c724c7ab61cb71f890a5fe6a1d18fc6

PiperOrigin-RevId: 140550061
---
 api/current.txt                               |  1 +
 res/values/attrs.xml                          |  4 +
 .../support/design/widget/AppBarLayout.java   | 92 +++++++++++++------
 3 files changed, 71 insertions(+), 26 deletions(-)

diff --git a/api/current.txt b/api/current.txt
index 30da82ab5..2506089c1 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -49,6 +49,7 @@ package android.support.design.widget {
     field public static final int SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED = 8; // 0x8
     field public static final int SCROLL_FLAG_EXIT_UNTIL_COLLAPSED = 2; // 0x2
     field public static final int SCROLL_FLAG_SCROLL = 1; // 0x1
+    field public static final int SCROLL_FLAG_SNAP = 16; // 0x10
   }
 
   public static abstract interface AppBarLayout.OnOffsetChangedListener {
diff --git a/res/values/attrs.xml b/res/values/attrs.xml
index 478c07b09..a89d9a23b 100644
--- a/res/values/attrs.xml
+++ b/res/values/attrs.xml
@@ -207,6 +207,10 @@
                  reached the end of it's scroll range, the remainder of this view will be scrolled
                  into view. -->
             <flag name="enterAlwaysCollapsed" value="0x8"/>
+
+            <!-- Upon a scroll ending, if the view is only partially visible then it will be
+                 snapped and scrolled to it's closest edge. -->
+            <flag name="snap" value="0x10"/>
         </attr>
 
         <!-- An interpolator to use when scrolling this View. Only takes effect when View
diff --git a/src/android/support/design/widget/AppBarLayout.java b/src/android/support/design/widget/AppBarLayout.java
index 262caa014..327a3cc67 100644
--- a/src/android/support/design/widget/AppBarLayout.java
+++ b/src/android/support/design/widget/AppBarLayout.java
@@ -492,7 +492,8 @@ public class AppBarLayout extends LinearLayout {
                 SCROLL_FLAG_SCROLL,
                 SCROLL_FLAG_EXIT_UNTIL_COLLAPSED,
                 SCROLL_FLAG_ENTER_ALWAYS,
-                SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED
+                SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED,
+                SCROLL_FLAG_SNAP
         })
         @Retention(RetentionPolicy.SOURCE)
         public @interface ScrollFlags {}
@@ -532,9 +533,18 @@ public class AppBarLayout extends LinearLayout {
         public static final int SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED = 0x8;
 
         /**
-         * Internal flag which allows quick checking of 'quick return'
+         * Upon a scroll ending, if the view is only partially visible then it will be snapped
+         * and scrolled to it's closest edge. For example, if the view only has it's bottom 25%
+         * displayed, it will be scrolled off screen completely. Conversely, if it's bottom 75%
+         * is visible then it will be scrolled fully into view.
+         */
+        public static final int SCROLL_FLAG_SNAP = 0x10;
+
+        /**
+         * Internal flags which allows quick checking features
          */
         static final int FLAG_QUICK_RETURN = SCROLL_FLAG_SCROLL | SCROLL_FLAG_ENTER_ALWAYS;
+        static final int FLAG_SNAP = SCROLL_FLAG_SCROLL | SCROLL_FLAG_SNAP;
 
         int mScrollFlags = SCROLL_FLAG_SCROLL;
         Interpolator mScrollInterpolator;
@@ -582,8 +592,8 @@ public class AppBarLayout extends LinearLayout {
          * Set the scrolling flags.
          *
          * @param flags bitwise int of {@link #SCROLL_FLAG_SCROLL},
-         *             {@link #SCROLL_FLAG_EXIT_UNTIL_COLLAPSED}, {@link #SCROLL_FLAG_ENTER_ALWAYS}
-         *             and {@link #SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED}.
+         *             {@link #SCROLL_FLAG_EXIT_UNTIL_COLLAPSED}, {@link #SCROLL_FLAG_ENTER_ALWAYS},
+         *             {@link #SCROLL_FLAG_ENTER_ALWAYS_COLLAPSED} and {@link #SCROLL_FLAG_SNAP }.
          *
          * @see #getScrollFlags()
          *
@@ -641,6 +651,7 @@ public class AppBarLayout extends LinearLayout {
         private int mOffsetDelta;
 
         private boolean mSkipNestedPreScroll;
+        private boolean mWasFlung;
         private Runnable mFlingRunnable;
         private ScrollerCompat mScroller;
 
@@ -719,10 +730,16 @@ public class AppBarLayout extends LinearLayout {
         }
 
         @Override
-        public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child,
+        public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl,
                 View target) {
-            // Reset the skip flag
+            if (!mWasFlung) {
+                // If we haven't been flung then let's see if the current view has been set to snap
+                snapToChildIfNeeded(coordinatorLayout, abl);
+            }
+
+            // Reset the flags
             mSkipNestedPreScroll = false;
+            mWasFlung = false;
             // Keep a reference to the previous nested scrolling child
             mLastNestedScrollingChildRef = new WeakReference<>(target);
         }
@@ -840,41 +857,39 @@ public class AppBarLayout extends LinearLayout {
         public boolean onNestedFling(final CoordinatorLayout coordinatorLayout,
                 final AppBarLayout child, View target, float velocityX, float velocityY,
                 boolean consumed) {
+            boolean flung = false;
+
             if (!consumed) {
                 // It has been consumed so let's fling ourselves
-                return fling(coordinatorLayout, child, -child.getTotalScrollRange(), 0, -velocityY);
+                flung = fling(coordinatorLayout, child, -child.getTotalScrollRange(),
+                        0, -velocityY);
             } else {
                 // If we're scrolling up and the child also consumed the fling. We'll fake scroll
                 // upto our 'collapsed' offset
-                int targetScroll;
                 if (velocityY < 0) {
                     // We're scrolling down
-                    targetScroll = -child.getTotalScrollRange()
+                    final int targetScroll = -child.getTotalScrollRange()
                             + child.getDownNestedPreScrollRange();
-
-                    if (getTopBottomOffsetForScrollingSibling() > targetScroll) {
-                        // If we're currently expanded more than the target scroll, we'll return false
-                        // now. This is so that we don't 'scroll' the wrong way.
-                        return false;
+                    if (getTopBottomOffsetForScrollingSibling() < targetScroll) {
+                        // If we're currently not expanded more than the target scroll, we'll
+                        // animate a fling
+                        animateOffsetTo(coordinatorLayout, child, targetScroll);
+                        flung = true;
                     }
                 } else {
                     // We're scrolling up
-                    targetScroll = -child.getUpNestedPreScrollRange();
-
-                    if (getTopBottomOffsetForScrollingSibling() < targetScroll) {
-                        // If we're currently expanded less than the target scroll, we'll return
-                        // false now. This is so that we don't 'scroll' the wrong way.
-                        return false;
+                    final int targetScroll = -child.getUpNestedPreScrollRange();
+                    if (getTopBottomOffsetForScrollingSibling() > targetScroll) {
+                        // If we're currently not expanded less than the target scroll, we'll
+                        // animate a fling
+                        animateOffsetTo(coordinatorLayout, child, targetScroll);
+                        flung = true;
                     }
                 }
-
-                if (getTopBottomOffsetForScrollingSibling() != targetScroll) {
-                    animateOffsetTo(coordinatorLayout, child, targetScroll);
-                    return true;
-                }
             }
 
-            return false;
+            mWasFlung = flung;
+            return flung;
         }
 
         private void animateOffsetTo(final CoordinatorLayout coordinatorLayout,
@@ -923,6 +938,31 @@ public class AppBarLayout extends LinearLayout {
             }
         }
 
+        private View getChildOnOffset(AppBarLayout abl, final int offset) {
+            for (int i = 0, count = abl.getChildCount(); i < count; i++) {
+                View child = abl.getChildAt(i);
+                if (child.getTop() <= -offset && child.getBottom() >= -offset) {
+                    return child;
+                }
+            }
+            return null;
+        }
+
+        private void snapToChildIfNeeded(CoordinatorLayout coordinatorLayout, AppBarLayout abl) {
+            final int offset = getTopBottomOffsetForScrollingSibling();
+            final View offsetChild = getChildOnOffset(abl, offset);
+            if (offsetChild != null) {
+                final LayoutParams lp = (LayoutParams) offsetChild.getLayoutParams();
+                if ((lp.getScrollFlags() & LayoutParams.FLAG_SNAP) == LayoutParams.FLAG_SNAP) {
+                    // We're set the snap, so animate the offset to the nearest edge
+                    final int childTop = -offsetChild.getTop();
+                    final int childBottom = -offsetChild.getBottom();
+                    animateOffsetTo(coordinatorLayout, abl,
+                            offset < (childBottom + childTop) / 2 ? childBottom : childTop);
+                }
+            }
+        }
+
         private class FlingRunnable implements Runnable {
             private final CoordinatorLayout mParent;
             private final AppBarLayout mLayout;