Overscrolling with Collapsing Toolbar

OverscrollingAppBarBehavior.java

import android.content.Context;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.util.AttributeSet;
import android.view.View;

@SuppressWarnings("unused")
public class OverscrollingAppBarBehavior extends AppBarLayout.Behavior {

    @SuppressWarnings("unused")
    public OverscrollingAppBarBehavior() {
    }

    @SuppressWarnings("unused")
    public OverscrollingAppBarBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy,
                                  int[] consumed) {
        if (OverscrollingScrollViewBehavior.isAssociatedWith(target)) {
            final OverscrollingScrollViewBehavior behavior = OverscrollingScrollViewBehavior.from(target);
            if (behavior.getState() != OverscrollingScrollViewBehavior.STATE_DISABLED) {
                return;
            }
        }
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
    }

    @Override
    public void onNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dxConsumed,
                               int dyConsumed, int dxUnconsumed, int dyUnconsumed) {
        if (OverscrollingScrollViewBehavior.isAssociatedWith(target)) {
            final OverscrollingScrollViewBehavior behavior = OverscrollingScrollViewBehavior.from(target);
            if (behavior.getState() != OverscrollingScrollViewBehavior.STATE_DISABLED) {
                return;
            }
        }
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
    }

    @Override
    public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl, View target) {
        if (OverscrollingScrollViewBehavior.isAssociatedWith(target)) {
            final OverscrollingScrollViewBehavior behavior = OverscrollingScrollViewBehavior.from(target);
            if (behavior.getState() != OverscrollingScrollViewBehavior.STATE_DISABLED) {
                return;
            }
        }
        super.onStopNestedScroll(coordinatorLayout, abl, target);
    }
}

OverscrollingScrollViewBehavior.java

import android.content.Context;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.annotation.IntDef;
import android.support.annotation.NonNull;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.os.ParcelableCompat;
import android.support.v4.os.ParcelableCompatCreatorCallbacks;
import android.support.v4.view.AbsSavedState;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.NestedScrollingChild;
import android.support.v4.view.VelocityTrackerCompat;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;

import com.hoteltonight.android.prod.util.Utilities;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.ref.WeakReference;

@SuppressWarnings("unused")
public class OverscrollingScrollViewBehavior extends AppBarLayout.ScrollingViewBehavior {
    /**
     * Callback for monitoring events about bottom sheets.
     */
    public abstract static class OverscrollingCallback {

        /**
         * Called when the bottom sheet changes its state.
         *
         * @param bottomSheet The bottom sheet view.
         * @param newState    The new state. This will be one of {@link #STATE_DRAGGING},
         *                    {@link #STATE_SETTLING}, {@link #STATE_EXPANDED},
         *                    {@link #STATE_DISABLED}, or {@link #STATE_HIDDEN}.
         */
        public abstract void onStateChanged(@NonNull View bottomSheet, @State int newState);

        /**
         * Called when the bottom sheet is being dragged.
         *
         * @param bottomSheet The bottom sheet view.
         * @param slideOffset The new offset of this bottom sheet within [-1,1] range. Offset
         *                    increases as this bottom sheet is moving upward. From 0 to 1 the sheet
         *                    is between collapsed and expanded states and from -1 to 0 it is
         *                    between hidden and collapsed states.
         */
        public abstract void onSlide(@NonNull View bottomSheet, float slideOffset);
    }

    /**
     * The bottom sheet is dragging.
     */
    public static final int STATE_DRAGGING = 1;

    /**
     * The bottom sheet is settling.
     */
    public static final int STATE_SETTLING = 2;

    /**
     * The bottom sheet is expanded.
     */
    public static final int STATE_EXPANDED = 3;

    /**
     * The bottom sheet is collapsed.
     */
    public static final int STATE_DISABLED = 4;

    /**
     * The bottom sheet is hidden.
     */
    public static final int STATE_HIDDEN = 5;

    @IntDef({STATE_EXPANDED, STATE_DISABLED, STATE_DRAGGING, STATE_SETTLING, STATE_HIDDEN})
    @Retention(RetentionPolicy.SOURCE)
    public @interface State {
    }

    private static final float HIDE_THRESHOLD = 0.5f;

    private static final float HIDE_FRICTION = 0.1f;

    private float mMaximumVelocity;

    private int mPeekHeight;

    private boolean mPeekHeightAuto;

    private int mPeekHeightMin;

    int mMinOffset;

    int mMaxOffset;

    boolean mHideable = true;

    @State
    int mState = STATE_DISABLED;

    ViewDragHelper mViewDragHelper;

    private boolean mIgnoreEvents;

    private int mLastNestedScrollDy;

    private boolean mNestedScrolled;

    int mParentHeight;

    WeakReference<View> mViewRef;

    WeakReference<View> mNestedScrollingChildRef;

    private OverscrollingCallback mCallback;

    private VelocityTracker mVelocityTracker;

    int mActivePointerId;

    private int mInitialY;

    boolean mTouchingScrollingChild;

    /**
     * Default constructor for instantiating BottomSheetBehaviors.
     */
    public OverscrollingScrollViewBehavior() {
    }

    /**
     * Default constructor for inflating BottomSheetBehaviors from layout.
     *
     * @param context The {@link Context}.
     * @param attrs   The {@link AttributeSet}.
     */
    public OverscrollingScrollViewBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
        ViewConfiguration configuration = ViewConfiguration.get(context);
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
    }

    @Override
    public Parcelable onSaveInstanceState(CoordinatorLayout parent, View child) {
        return new SavedState(super.onSaveInstanceState(parent, child), mState);
    }

    @Override
    public void onRestoreInstanceState(CoordinatorLayout parent, View child, Parcelable state) {
        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(parent, child, ss.getSuperState());
        // Intermediate states are restored as collapsed state
        if (ss.state == STATE_DRAGGING || ss.state == STATE_SETTLING) {
            mState = STATE_DISABLED;
        } else {
            mState = ss.state;
        }
    }


    @Override
    public boolean onLayoutChild(CoordinatorLayout parent, View child, int layoutDirection) {
        super.onLayoutChild(parent, child, layoutDirection);
        if (ViewCompat.getFitsSystemWindows(parent) && !ViewCompat.getFitsSystemWindows(child)) {
            ViewCompat.setFitsSystemWindows(child, true);
        }
        int savedTop = child.getTop();
        // First let the parent lay it out
        parent.onLayoutChild(child, layoutDirection);
        // Offset the bottom sheet
        mParentHeight = parent.getHeight();
        int peekHeight = mPeekHeight;
        mMinOffset = Math.max(savedTop, mParentHeight - child.getHeight());
        mMaxOffset = Math.max(mParentHeight - peekHeight, mMinOffset);
        if (mState == STATE_EXPANDED) {
            ViewCompat.offsetTopAndBottom(child, mMinOffset);
        } else if (mHideable && mState == STATE_HIDDEN) {
            ViewCompat.offsetTopAndBottom(child, mParentHeight);
        } else if (mState == STATE_DRAGGING || mState == STATE_SETTLING) {
            ViewCompat.offsetTopAndBottom(child, savedTop - child.getTop());
        }
        if (mViewDragHelper == null) {
            mViewDragHelper = ViewDragHelper.create(parent, mDragCallback);
        }
        mViewRef = new WeakReference<>(child);
        mNestedScrollingChildRef = new WeakReference<>(findScrollingChild(child));
        return true;
    }

    @Override
    public boolean onInterceptTouchEvent(CoordinatorLayout parent, View child, MotionEvent event) {
        if (!child.isShown()) {
            mIgnoreEvents = true;
            return false;
        }
        int action = MotionEventCompat.getActionMasked(event);
        // Record the velocity
        if (action == MotionEvent.ACTION_DOWN) {
            reset();
        }
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
        switch (action) {
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mTouchingScrollingChild = false;
                mActivePointerId = MotionEvent.INVALID_POINTER_ID;
                // Reset the ignore flag
                if (mIgnoreEvents) {
                    mIgnoreEvents = false;
                    return false;
                }
                break;
            case MotionEvent.ACTION_DOWN:
                int initialX = (int) event.getX();
                mInitialY = (int) event.getY();
                View scroll = mNestedScrollingChildRef.get();
                if (scroll != null && parent.isPointInChildBounds(scroll, initialX, mInitialY)) {
                    mActivePointerId = event.getPointerId(event.getActionIndex());
                    mTouchingScrollingChild = true;
                }
                mIgnoreEvents = mActivePointerId == MotionEvent.INVALID_POINTER_ID &&
                        !parent.isPointInChildBounds(child, initialX, mInitialY);
                break;
        }
        if (!mIgnoreEvents && mViewDragHelper.shouldInterceptTouchEvent(event)) {
            return true;
        }
        // We have to handle cases that the ViewDragHelper does not capture the bottom sheet because
        // it is not the top most view of its parent. This is not necessary when the touch event is
        // happening over the scrolling content as nested scrolling logic handles that case.
        View scroll = mNestedScrollingChildRef.get();
        return action == MotionEvent.ACTION_MOVE && scroll != null &&
                !mIgnoreEvents && mState != STATE_DRAGGING &&
                !parent.isPointInChildBounds(scroll, (int) event.getX(), (int) event.getY()) &&
                Math.abs(mInitialY - event.getY()) > mViewDragHelper.getTouchSlop();
    }

    @Override
    public boolean onTouchEvent(CoordinatorLayout parent, View child, MotionEvent event) {
        if (!child.isShown()) {
            return false;
        }
        int action = MotionEventCompat.getActionMasked(event);
        if (mState == STATE_DRAGGING && action == MotionEvent.ACTION_DOWN) {
            return true;
        }
        mViewDragHelper.processTouchEvent(event);
        // Record the velocity
        if (action == MotionEvent.ACTION_DOWN) {
            reset();
        }
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(event);
        // The ViewDragHelper tries to capture only the top-most View. We have to explicitly tell it
        // to capture the bottom sheet in case it is not captured and the touch slop is passed.
        if (action == MotionEvent.ACTION_MOVE && !mIgnoreEvents) {
            if (Math.abs(mInitialY - event.getY()) > mViewDragHelper.getTouchSlop()) {
                mViewDragHelper.captureChildView(child, event.getPointerId(event.getActionIndex()));
            }
        }
        return !mIgnoreEvents;
    }

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child,
                                       View directTargetChild, View target, int nestedScrollAxes) {
        mLastNestedScrollDy = 0;
        mNestedScrolled = false;
        return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx,
                                  int dy, int[] consumed) {
        View scrollingChild = mNestedScrollingChildRef.get();
        if (target != scrollingChild || mState == STATE_DISABLED) {
            return;
        }
        int currentTop = child.getTop();
        int newTop = currentTop - dy;
        if (dy > 0) { // Upward
            if (newTop == mMinOffset) {
                consumed[1] = dy;
                ViewCompat.offsetTopAndBottom(child, -dy);
                setStateInternal(STATE_EXPANDED);
            } else if (newTop < mMinOffset) {
                consumed[1] = currentTop - mMinOffset;
                ViewCompat.offsetTopAndBottom(child, -consumed[1]);
                setStateInternal(STATE_DISABLED);
            } else {
                consumed[1] = dy;
                ViewCompat.offsetTopAndBottom(child, -dy);
                setStateInternal(STATE_DRAGGING);
            }
        } else if (dy < 0) { // Downward
            if (!ViewCompat.canScrollVertically(target, -1)) {
                if (newTop <= mMaxOffset || mHideable) {
                    consumed[1] = dy;
                    ViewCompat.offsetTopAndBottom(child, -dy);
                    setStateInternal(STATE_DRAGGING);
                }
            }
        }
        dispatchOnSlide(child.getTop());
        mLastNestedScrollDy = dy;
        mNestedScrolled = mState != STATE_DISABLED;
    }

    @Override
    public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, View child, View target) {
        if (mState != STATE_DISABLED && child.getTop() == mMinOffset) {
            setStateInternal(STATE_EXPANDED);
            return;
        }
        if (target != mNestedScrollingChildRef.get() || !mNestedScrolled) {
            return;
        }
        int top;
        int targetState;
        if (mLastNestedScrollDy > 0) {
            top = mMinOffset;
            targetState = STATE_EXPANDED;
        } else if (mHideable && shouldHide(child, getYVelocity())) {
            top = mParentHeight;
            targetState = STATE_HIDDEN;
        } else {
            top = mMinOffset;
            targetState = STATE_EXPANDED;
        }
        if (mViewDragHelper.smoothSlideViewTo(child, child.getLeft(), top)) {
            setStateInternal(STATE_SETTLING);
            ViewCompat.postOnAnimation(child, new SettleRunnable(child, targetState));
        } else {
            setStateInternal(targetState);
        }
        mNestedScrolled = false;
    }

    @Override
    public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, View child, View target,
                                    float velocityX, float velocityY) {
        return target == mNestedScrollingChildRef.get() &&
                ((mState != STATE_EXPANDED && mState != STATE_DISABLED) ||
                        super.onNestedPreFling(coordinatorLayout, child, target,
                                velocityX, velocityY));
    }

    /**
     * Sets a callback to be notified of bottom sheet events.
     *
     * @param callback The callback to notify when bottom sheet events occur.
     */
    public void setOverscrollingCallback(OverscrollingCallback callback) {
        mCallback = callback;
    }

    /**
     * Sets the state of the overscrolling. Will transition to that state with
     * animation.
     *
     * @param state One of {@link #STATE_DISABLED}, {@link #STATE_EXPANDED}, or
     *              {@link #STATE_HIDDEN}.
     */
    public final void setState(final @State int state) {
        if (state == mState) {
            return;
        }
        if (state == STATE_DISABLED) {
            mState = STATE_DISABLED;
            return;
        }
        if (mViewRef == null) {
            // The view is not laid out yet; modify mState and let onLayoutChild handle it later
            if (state == STATE_EXPANDED || mHideable && state == STATE_HIDDEN) {
                mState = state;
            }
            return;
        }
        final View child = mViewRef.get();
        if (child == null) {
            return;
        }
        // Start the animation; wait until a pending layout if there is one.
        ViewParent parent = child.getParent();
        if (parent != null && parent.isLayoutRequested() && ViewCompat.isAttachedToWindow(child)) {
            child.post(new Runnable() {
                @Override
                public void run() {
                    startSettlingAnimation(child, state);
                }
            });
        } else {
            startSettlingAnimation(child, state);
        }
    }

    /**
     * Gets the current state of the overscrolling.
     *
     * @return One of {@link #STATE_EXPANDED}, {@link #STATE_DISABLED}, {@link #STATE_DRAGGING},
     * and {@link #STATE_SETTLING}.
     */
    @State
    public final int getState() {
        return mState;
    }

    void setStateInternal(@State int state) {
        if (mState == state) {
            return;
        }
        mState = state;
        View view = mViewRef.get();
        if (view != null && mCallback != null) {
            mCallback.onStateChanged(view, state);
        }
    }

    private void reset() {
        mActivePointerId = ViewDragHelper.INVALID_POINTER;
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    boolean shouldHide(View child, float yvel) {
        final float newTop = child.getTop() + yvel * HIDE_FRICTION;
        return Math.abs(newTop) / (float) mParentHeight > HIDE_THRESHOLD;
    }

    private static View findScrollingChild(View view) {
        if (view instanceof NestedScrollingChild) {
            return view;
        }
        if (view instanceof ViewGroup) {
            ViewGroup group = (ViewGroup) view;
            for (int i = 0, count = group.getChildCount(); i < count; i++) {
                View scrollingChild = findScrollingChild(group.getChildAt(i));
                if (scrollingChild != null) {
                    return scrollingChild;
                }
            }
        }
        return null;
    }

    private float getYVelocity() {
        mVelocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
        return VelocityTrackerCompat.getYVelocity(mVelocityTracker, mActivePointerId);
    }

    void startSettlingAnimation(View child, int state) {
        int top;
        if (state == STATE_EXPANDED) {
            top = mMinOffset;
        } else if (mHideable && state == STATE_HIDDEN) {
            top = mParentHeight;
        } else {
            throw new IllegalArgumentException("Illegal state argument: " + state);
        }
        setStateInternal(STATE_SETTLING);
        if (mViewDragHelper.smoothSlideViewTo(child, child.getLeft(), top)) {
            ViewCompat.postOnAnimation(child, new SettleRunnable(child, state));
        }
    }

    private final ViewDragHelper.Callback mDragCallback = new ViewDragHelper.Callback() {

        @Override
        public boolean tryCaptureView(View child, int pointerId) {
            if (mState == STATE_DRAGGING) {
                return false;
            }
            if (mTouchingScrollingChild) {
                return false;
            }
            if (mState == STATE_EXPANDED && mActivePointerId == pointerId) {
                View scroll = mNestedScrollingChildRef.get();
                if (scroll != null && ViewCompat.canScrollVertically(scroll, -1)) {
                    // Let the content scroll up
                    return false;
                }
            }
            return mViewRef != null && mViewRef.get() == child;
        }

        @Override
        public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
            dispatchOnSlide(top);
        }

        @Override
        public void onViewDragStateChanged(int state) {
            if (state == ViewDragHelper.STATE_DRAGGING) {
                setStateInternal(STATE_DRAGGING);
            }
        }

        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel) {
            int top;
            @State int targetState;
            if (yvel < 0) { // Moving up
                top = mMinOffset;
                targetState = STATE_EXPANDED;
            } else if (shouldHide(releasedChild, yvel)) {
                top = mParentHeight;
                targetState = STATE_HIDDEN;
            } else if (yvel == 0.f) {
                int currentTop = releasedChild.getTop();
                top = mMinOffset;
                targetState = STATE_EXPANDED;
            } else {
                top = mMinOffset;
                targetState = STATE_EXPANDED;
            }
            if (mViewDragHelper.settleCapturedViewAt(releasedChild.getLeft(), top)) {
                setStateInternal(STATE_SETTLING);
                ViewCompat.postOnAnimation(releasedChild,
                        new SettleRunnable(releasedChild, targetState));
            } else {
                setStateInternal(targetState);
            }
        }

        @Override
        public int clampViewPositionVertical(View child, int top, int dy) {
            return Utilities.constrain(top, mMinOffset, mParentHeight);
        }

        @Override
        public int clampViewPositionHorizontal(View child, int left, int dx) {
            return child.getLeft();
        }

        @Override
        public int getViewVerticalDragRange(View child) {
            if (mHideable) {
                return mParentHeight - mMinOffset;
            } else {
                return mMaxOffset - mMinOffset;
            }
        }
    };

    void dispatchOnSlide(int top) {
        View view = mViewRef.get();
        if (view != null && mCallback != null) {
            if (top > mMaxOffset) {
                mCallback.onSlide(view, (float) (mMaxOffset - top) /
                        (mParentHeight - mMaxOffset));
            } else {
                mCallback.onSlide(view,
                        (float) (mMaxOffset - top) / ((mMaxOffset - mMinOffset)));
            }
        }
    }

    private class SettleRunnable implements Runnable {

        private final View mView;

        @State
        private final int mTargetState;

        SettleRunnable(View view, @State int targetState) {
            mView = view;
            mTargetState = targetState;
        }

        @Override
        public void run() {
            if (mViewDragHelper != null && mViewDragHelper.continueSettling(true)) {
                ViewCompat.postOnAnimation(mView, this);
            } else {
                setStateInternal(mTargetState);
            }
        }
    }

    protected static class SavedState extends AbsSavedState {
        @State
        final int state;

        public SavedState(Parcel source) {
            this(source, null);
        }

        public SavedState(Parcel source, ClassLoader loader) {
            super(source, loader);
            //noinspection ResourceType
            state = source.readInt();
        }

        public SavedState(Parcelable superState, @State int state) {
            super(superState);
            this.state = state;
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(state);
        }

        public static final Creator<SavedState> CREATOR = ParcelableCompat.newCreator(
                new ParcelableCompatCreatorCallbacks<SavedState>() {
                    @Override
                    public SavedState createFromParcel(Parcel in, ClassLoader loader) {
                        return new SavedState(in, loader);
                    }

                    @Override
                    public SavedState[] newArray(int size) {
                        return new SavedState[size];
                    }
                });
    }

    /**
     * A utility function to get the {@link OverscrollingScrollViewBehavior} associated with the {@code view}.
     *
     * @param view The {@link View} with {@link OverscrollingScrollViewBehavior}.
     * @return The {@link OverscrollingScrollViewBehavior} associated with the {@code view}.
     */
    @SuppressWarnings("unchecked")
    public static OverscrollingScrollViewBehavior from(View view) {
        ViewGroup.LayoutParams params = view.getLayoutParams();
        if (!(params instanceof CoordinatorLayout.LayoutParams)) {
            throw new IllegalArgumentException("The view is not a child of CoordinatorLayout");
        }
        CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params).getBehavior();
        if (!(behavior instanceof OverscrollingScrollViewBehavior)) {
            throw new IllegalArgumentException(
                    "The view is not associated with BottomSheetBehavior");
        }
        return (OverscrollingScrollViewBehavior) behavior;
    }

    /**
     * A utility function to check for {@link OverscrollingScrollViewBehavior} associated with the {@code view}.
     *
     * @param view The {@link View} with {@link OverscrollingScrollViewBehavior}.
     * @return {@code true} if there's an {@link OverscrollingScrollViewBehavior} associated with the {@code view}.
     */
    @SuppressWarnings("unchecked")
    public static boolean isAssociatedWith(View view) {
        ViewGroup.LayoutParams params = view.getLayoutParams();
        if (!(params instanceof CoordinatorLayout.LayoutParams)) {
            return false;
        }
        CoordinatorLayout.Behavior behavior = ((CoordinatorLayout.LayoutParams) params).getBehavior();
        return behavior instanceof OverscrollingScrollViewBehavior;
    }
}

SomeActivity.java

public void onCreate(Bundle icicle) {
        super.onCreate(icicle);
        /**
         * ...
         */
        appBar = (AppBarLayout) view.findViewById(R.id.appBar);
        final ViewGroup.MarginLayoutParams searchControlMargins =
                (ViewGroup.MarginLayoutParams) searchControlsView.getLayoutParams();
        expandedAppBarMargin = searchControlMargins.leftMargin;

        // Setup the overscrolls
        final View appBarChild = appBar.getChildAt(0);
        final int minHeight = ViewCompat.getMinimumHeight(appBarChild);
        final OverscrollingScrollViewBehavior behavior = OverscrollingScrollViewBehavior.from(hotelList);
        appBar.addOnOffsetChangedListener((appBarLayout, verticalOffset) -> {
            final int scrollRange = appBar.getTotalScrollRange() - minHeight;
            if (mCurrentState != STATE_EXPANDED && verticalOffset == 0) {
                // Re-enable Overscrolling when settled back into default state
                behavior.setState(OverscrollingScrollViewBehavior.STATE_EXPANDED);
                mCurrentState = STATE_EXPANDED;
            } else if (mCurrentState != STATE_COLLAPSED && Math.abs(verticalOffset) >= scrollRange) {
                mCurrentState = STATE_COLLAPSED;
            } else {
                mCurrentState = STATE_TRANSITIONING;
            }
        });
        behavior.setState(OverscrollingScrollViewBehavior.STATE_EXPANDED); 
}

what about Utilities.constrain method?

Yes, the Utilities.constrain method is missing.