activity_slidingupscrollview.xml

<!--
  Copyright 2014 Soichiro Kashima

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:clipChildren="false"
    android:orientation="vertical">

    <!--
    Dummy background contents.
    You can replace this to map or something.
    -->
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#E91E63" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#3F51B5" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#2196F3" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#03A9F4" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#8BC34A" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#FFEB3B" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#FFC107" />

        <View
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="#FF9800" />
    </LinearLayout>

    <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="@dimen/flexible_space_image_height"
        android:scaleType="centerCrop"
        android:src="@drawable/example" />

    <com.github.ksoichiro.android.observablescrollview.TouchInterceptionFrameLayout
        android:id="@+id/scroll_wrapper"
        android:clipChildren="false"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <com.github.ksoichiro.android.observablescrollview.ObservableScrollView
            android:id="@+id/scroll"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_marginTop="@dimen/header_bar_height"
            android:background="@android:color/white"
            android:fillViewport="true">

            <TextView
                android:id="@+id/container"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:paddingBottom="@dimen/activity_vertical_margin"
                android:paddingLeft="@dimen/activity_horizontal_margin"
                android:paddingRight="@dimen/activity_horizontal_margin"
                android:paddingTop="@dimen/activity_vertical_margin"
                android:text="@string/lipsum" />
        </com.github.ksoichiro.android.observablescrollview.ObservableScrollView>

        <FrameLayout
            android:id="@+id/header"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:clipChildren="false">

            <View
                android:id="@+id/header_background"
                android:layout_width="match_parent"
                android:layout_height="@dimen/header_bar_height"
                android:background="?attr/colorPrimary"
                android:minHeight="@dimen/header_bar_height" />

            <LinearLayout
                android:id="@+id/header_bar"
                android:layout_width="match_parent"
                android:layout_height="@dimen/header_bar_height"
                android:background="@android:color/white"
                android:minHeight="@dimen/header_bar_height"
                android:orientation="vertical">

                <TextView
                    android:id="@+id/title"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    android:ellipsize="end"
                    android:gravity="center_vertical"
                    android:maxLines="1"
                    android:paddingLeft="@dimen/margin_standard"
                    android:textColor="@android:color/black"
                    android:textSize="20sp" />
            </LinearLayout>

            <LinearLayout
                android:id="@+id/header_overlay"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="vertical">

                <View
                    android:id="@+id/header_flexible_space"
                    android:layout_width="match_parent"
                    android:layout_height="0dp"
                    android:background="?attr/colorPrimary" />

                <View
                    android:layout_width="match_parent"
                    android:layout_height="@dimen/sliding_overlay_blur_size"
                    android:background="@drawable/sliding_header_overlay"
                    android:minHeight="@dimen/sliding_overlay_blur_size" />
            </LinearLayout>

            <com.melnykov.fab.FloatingActionButton
                android:id="@+id/fab"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:scaleType="center"
                app:fab_colorNormal="@color/accentLight"
                app:fab_colorPressed="@color/accent" />
        </FrameLayout>
    </com.github.ksoichiro.android.observablescrollview.TouchInterceptionFrameLayout>

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_gravity="top"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="?attr/colorPrimary"
        android:minHeight="?attr/actionBarSize"
        app:popupTheme="@style/Theme.AppCompat.Light.DarkActionBar"
        app:theme="@style/Toolbar" />

    <TextView
        android:id="@+id/toolbar_title"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:ellipsize="end"
        android:gravity="center_vertical"
        android:maxLines="1"
        android:paddingLeft="@dimen/toolbar_margin_start"
        android:paddingRight="@dimen/margin_extra_short"
        android:textColor="@android:color/white"
        android:textSize="20sp" />
</FrameLayout>

dimens.xml

<!--
  Copyright 2014 Soichiro Kashima

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->
<resources>
    <!-- Default screen margins, per the Android Design guidelines. -->
    <dimen name="activity_horizontal_margin">16dp</dimen>
    <dimen name="activity_vertical_margin">16dp</dimen>

    <dimen name="margin_standard">16dp</dimen>
    <dimen name="margin_short">8dp</dimen>
    <dimen name="margin_extra_short">4dp</dimen>

    <dimen name="toolbar_elevation">4dp</dimen>

    <dimen name="toolbar_margin_start">72dp</dimen>
    <dimen name="flexible_space_height">72dp</dimen>
    <dimen name="flexible_space_image_height">240dp</dimen>
    <dimen name="flexible_space_show_fab_offset">120dp</dimen>

    <dimen name="parallax_image_height">180dp</dimen>
    <dimen name="tab_height">48dp</dimen>

    <dimen name="header_bar_height">72dp</dimen>
    <dimen name="intersection_height">16dp</dimen>

    <dimen name="sliding_slop">32dp</dimen>
    <dimen name="sliding_overlay_blur_size">4dp</dimen>
</resources>

sliding_header_overlay.xml

<!--
  Copyright 2014 Soichiro Kashima

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
-->
<shape xmlns:android="http://schemas.android.com/apk/res/android">

    <gradient
        android:angle="270"
        android:endColor="#00009688"
        android:startColor="#FF009688" />

</shape>

SlidingUpBaseActivity.java

/*
 * Copyright 2014 Soichiro Kashima
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.github.ksoichiro.android.observablescrollview.samples;

import android.annotation.TargetApi;
import android.content.res.TypedArray;
import android.graphics.Color;
import android.graphics.Rect;
import android.graphics.drawable.ColorDrawable;
import android.os.Build;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewTreeObserver;
import android.widget.FrameLayout;
import android.widget.TextView;

import com.github.ksoichiro.android.observablescrollview.ObservableScrollViewCallbacks;
import com.github.ksoichiro.android.observablescrollview.ScrollState;
import com.github.ksoichiro.android.observablescrollview.Scrollable;
import com.github.ksoichiro.android.observablescrollview.TouchInterceptionFrameLayout;
import com.nineoldandroids.animation.ValueAnimator;
import com.nineoldandroids.view.ViewHelper;
import com.nineoldandroids.view.ViewPropertyAnimator;

public abstract class SlidingUpBaseActivity<S extends Scrollable> extends ActionBarActivity implements ObservableScrollViewCallbacks {

    private View mHeader;
    private View mHeaderBar;
    private View mHeaderOverlay;
    private View mHeaderFlexibleSpace;
    private TextView mTitle;
    private TextView mToolbarTitle;
    private View mImageView;
    private View mFab;
    private Toolbar mToolbar;
    private S mScrollable;
    private TouchInterceptionFrameLayout mInterceptionLayout;
    private int mActionBarSize;
    private int mIntersectionHeight;
    private int mHeaderBarHeight;
    private int mSlidingSlop;
    private int mSlidingHeaderBlueSize;
    private float mScrollYOnDownMotion;
    private boolean mMoved;
    private float mInitialY;
    private float mMovedDistanceY;
    private int mFabMargin;
    private boolean mFabIsShown;
    private int mFlexibleSpaceImageHeight;
    private int mToolbarColor;
    private boolean mHeaderColorChanging;
    private boolean mHeaderIsAtBottom;
    private boolean mHeaderIsNotAtBottom;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(getLayoutResId());

        mToolbar = (Toolbar) findViewById(R.id.toolbar);

        setSupportActionBar(mToolbar);
        ViewHelper.setScaleY(mToolbar, 0);
        getSupportActionBar().setHomeButtonEnabled(true);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        getSupportActionBar().setTitle("");

        mToolbarColor = getResources().getColor(R.color.primary);
        mToolbar.setBackgroundColor(Color.TRANSPARENT);
        mToolbar.setTitle("");

        mFlexibleSpaceImageHeight = getResources().getDimensionPixelSize(R.dimen.flexible_space_image_height);
        mIntersectionHeight = getResources().getDimensionPixelSize(R.dimen.intersection_height);
        mHeaderBarHeight = getResources().getDimensionPixelSize(R.dimen.header_bar_height);
        mSlidingSlop = getResources().getDimensionPixelSize(R.dimen.sliding_slop);
        mActionBarSize = getActionBarSize();
        mSlidingHeaderBlueSize = getResources().getDimensionPixelSize(R.dimen.sliding_overlay_blur_size);

        mHeader = findViewById(R.id.header);
        mHeaderBar = findViewById(R.id.header_bar);
        mHeaderOverlay = findViewById(R.id.header_overlay);
        mHeaderFlexibleSpace = findViewById(R.id.header_flexible_space);
        mImageView = findViewById(R.id.image);
        mImageView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                slideOnClick();
            }
        });
        mScrollable = createScrollable();

        mFab = findViewById(R.id.fab);
        mFabMargin = getResources().getDimensionPixelSize(R.dimen.margin_standard);
        mFabIsShown = true;

        mInterceptionLayout = (TouchInterceptionFrameLayout) findViewById(R.id.scroll_wrapper);
        mInterceptionLayout.setScrollInterceptionListener(mInterceptionListener);
        mTitle = (TextView) findViewById(R.id.title);
        mTitle.setText(getTitle());
        mToolbarTitle = (TextView) findViewById(R.id.toolbar_title);
        mToolbarTitle.setText(mTitle.getText());
        ViewHelper.setAlpha(mToolbarTitle, 0);
        ViewHelper.setTranslationY(mTitle, (mHeaderBarHeight - mActionBarSize) / 2);

        ViewTreeObserver vto = mInterceptionLayout.getViewTreeObserver();
        vto.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN) {
                    mInterceptionLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
                } else {
                    mInterceptionLayout.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                }
                ViewHelper.setTranslationY(mInterceptionLayout, getScreenHeight() - mHeaderBarHeight);
                ViewHelper.setTranslationY(mImageView, getScreenHeight() - mHeaderBarHeight);
                if (mFab != null) {
                    ViewHelper.setTranslationX(mFab, mTitle.getWidth() - mFabMargin - mFab.getWidth());
                    ViewHelper.setTranslationY(mFab, ViewHelper.getX(mTitle) - (mFab.getHeight() / 2));
                }
                changeHeaderBarColor();
                changeHeaderOverlay();
            }
        });
    }

    protected abstract int getLayoutResId();
    protected abstract S createScrollable();

    @Override
    public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) {
    }

    @Override
    public void onDownMotionEvent() {
    }

    @Override
    public void onUpOrCancelMotionEvent(ScrollState scrollState) {
    }

    private TouchInterceptionFrameLayout.TouchInterceptionListener mInterceptionListener = new TouchInterceptionFrameLayout.TouchInterceptionListener() {
        @Override
        public boolean shouldInterceptTouchEvent(MotionEvent ev, boolean moving, float diffX, float diffY) {
            final int minInterceptionLayoutY = -mIntersectionHeight;
            return minInterceptionLayoutY < (int) ViewHelper.getY(mInterceptionLayout)
                    || (moving && mScrollable.getCurrentScrollY() - diffY < 0);
        }

        @Override
        public void onDownMotionEvent(MotionEvent ev) {
            mScrollYOnDownMotion = mScrollable.getCurrentScrollY();
            mInitialY = ViewHelper.getTranslationY(mInterceptionLayout);
        }

        @Override
        public void onMoveMotionEvent(MotionEvent ev, float diffX, float diffY) {
            mMoved = true;
            float translationY = ViewHelper.getTranslationY(mInterceptionLayout) - mScrollYOnDownMotion + diffY;
            if (translationY < -mIntersectionHeight) {
                translationY = -mIntersectionHeight;
            } else if (getScreenHeight() - mHeaderBarHeight < translationY) {
                translationY = getScreenHeight() - mHeaderBarHeight;
            }

            slideTo(translationY);

            mMovedDistanceY = ViewHelper.getTranslationY(mInterceptionLayout) - mInitialY;
        }

        @Override
        public void onUpOrCancelMotionEvent(MotionEvent ev) {
            if (!mMoved) {
                // Invoke slide animation only on header view
                Rect outRect = new Rect();
                mHeader.getHitRect(outRect);
                if (outRect.contains((int) ev.getX(), (int) ev.getY())) {
                    slideOnClick();
                }
            } else {
                stickToAnchors();
            }
            mMoved = false;
        }
    };

    @TargetApi(Build.VERSION_CODES.HONEYCOMB)
    private void changeHeaderBarColor() {
        if (mHeaderColorChanging) {
            return;
        }
        boolean shouldBeWhite = getAnchorYBottom() == ViewHelper.getTranslationY(mInterceptionLayout);
        final int headerColorAtBottom = Color.WHITE;
        int color = ((ColorDrawable) mHeaderBar.getBackground()).getColor();
        if (!mHeaderIsAtBottom && color != headerColorAtBottom && shouldBeWhite) {
            mHeaderIsAtBottom = true;
            mHeaderIsNotAtBottom = false;
            ValueAnimator animator = ValueAnimator.ofFloat(0, 1).setDuration(100);
            animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    float alpha = (float) animation.getAnimatedValue();
                    mHeaderColorChanging = (alpha != 1);
                    setBackgroundAlpha(mHeaderBar, alpha, headerColorAtBottom);

                    int level = Math.min(255, Math.max(0, (int) ((1 - alpha) * 255)));
                    mTitle.setTextColor(0xff000000 + (0x010101 * level));
                }
            });
            animator.start();
        } else if (!mHeaderIsNotAtBottom && !shouldBeWhite) {
            mHeaderIsAtBottom = false;
            mHeaderIsNotAtBottom = true;
            ValueAnimator animator = ValueAnimator.ofFloat(1, 0).setDuration(100);
            animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    float alpha = (float) animation.getAnimatedValue();
                    mHeaderColorChanging = (alpha != 0);
                    setBackgroundAlpha(mHeaderBar, alpha, headerColorAtBottom);

                    int level = Math.min(255, Math.max(0, (int) ((1 - alpha) * 255)));
                    mTitle.setTextColor(0xff000000 + (0x010101 * level));
                }
            });
            animator.start();
        }
    }

    private void changeHeaderOverlay() {
        final float translationY = ViewHelper.getTranslationY(mInterceptionLayout);
        if (translationY <= mToolbar.getHeight() - mSlidingHeaderBlueSize) {
            mHeaderOverlay.setVisibility(View.VISIBLE);
            mHeaderFlexibleSpace.getLayoutParams().height = (int) (mToolbar.getHeight() - mSlidingHeaderBlueSize - translationY);
            mHeaderFlexibleSpace.requestLayout();
            mHeaderOverlay.requestLayout();
        } else {
            mHeaderOverlay.setVisibility(View.INVISIBLE);
        }
    }

    private void slideOnClick() {
        float translationY = ViewHelper.getTranslationY(mInterceptionLayout);
        if (translationY == getAnchorYBottom()) {
            slideWithAnimation(getAnchorYImage());
        } else if (translationY == getAnchorYImage()) {
            slideWithAnimation(getAnchorYBottom());
        }
    }

    private void stickToAnchors() {
        // Slide to some points automatically
        if (0 < mMovedDistanceY) {
            // Sliding down
            if (mSlidingSlop < mMovedDistanceY) {
                // Sliding down to an anchor
                if (getAnchorYImage() < ViewHelper.getTranslationY(mInterceptionLayout)) {
                    slideWithAnimation(getAnchorYBottom());
                } else {
                    slideWithAnimation(getAnchorYImage());
                }
            } else {
                // Sliding up(back) to an anchor
                if (getAnchorYImage() < ViewHelper.getTranslationY(mInterceptionLayout)) {
                    slideWithAnimation(getAnchorYImage());
                } else {
                    slideWithAnimation(0);
                }
            }
        } else if (mMovedDistanceY < 0) {
            // Sliding up
            if (mMovedDistanceY < -mSlidingSlop) {
                // Sliding up to an anchor
                if (getAnchorYImage() < ViewHelper.getTranslationY(mInterceptionLayout)) {
                    slideWithAnimation(getAnchorYImage());
                } else {
                    slideWithAnimation(0);
                }
            } else {
                // Sliding down(back) to an anchor
                if (getAnchorYImage() < ViewHelper.getTranslationY(mInterceptionLayout)) {
                    slideWithAnimation(getAnchorYBottom());
                } else {
                    slideWithAnimation(getAnchorYImage());
                }
            }
        }
    }

    private void slideTo(float translationY) {
        ViewHelper.setTranslationY(mInterceptionLayout, translationY);

        if (translationY < 0) {
            FrameLayout.LayoutParams lp = (FrameLayout.LayoutParams) mInterceptionLayout.getLayoutParams();
            lp.height = (int) -translationY + getScreenHeight();
            mInterceptionLayout.requestLayout();
        }

        // Translate title
        float hiddenHeight = translationY < 0 ? -translationY : 0;
        ViewHelper.setTranslationY(mTitle, Math.min(mIntersectionHeight, (mHeaderBarHeight + hiddenHeight - mActionBarSize) / 2));

        // Translate image
        float imageAnimatableHeight = getScreenHeight() - mHeaderBarHeight;
        float imageTranslationScale = imageAnimatableHeight / (imageAnimatableHeight - mImageView.getHeight());
        float imageTranslationY = Math.max(0, imageAnimatableHeight - (imageAnimatableHeight - translationY) * imageTranslationScale);
        ViewHelper.setTranslationY(mImageView, imageTranslationY);

        // Show/hide FAB
        if (ViewHelper.getTranslationY(mInterceptionLayout) < mFlexibleSpaceImageHeight) {
            hideFab();
        } else {
            ViewPropertyAnimator.animate(mToolbar).scaleY(0).setDuration(200).start();
            showFab();
        }
        if (ViewHelper.getTranslationY(mInterceptionLayout) <= mFlexibleSpaceImageHeight) {
            ViewPropertyAnimator.animate(mToolbar).scaleY(1).setDuration(200).start();
            setBackgroundAlpha(mToolbar, 0, mToolbarColor);
        }

        if (ViewHelper.getTranslationY(mInterceptionLayout) <= mIntersectionHeight) {
            if (ViewHelper.getAlpha(mToolbarTitle) == 0) {
                ViewPropertyAnimator.animate(mToolbarTitle).cancel();
                ViewPropertyAnimator.animate(mToolbarTitle).alpha(1).setDuration(200).start();
            }
        } else if (ViewHelper.getAlpha(mToolbarTitle) == 1) {
            ViewPropertyAnimator.animate(mToolbarTitle).cancel();
            ViewPropertyAnimator.animate(mToolbarTitle).alpha(0).setDuration(200).start();
        } else {
            ViewHelper.setAlpha(mToolbarTitle, 0);
        }
        changeHeaderBarColor();
        changeHeaderOverlay();
    }

    private void slideWithAnimation(float toY) {
        float layoutTranslationY = ViewHelper.getTranslationY(mInterceptionLayout);
        if (layoutTranslationY != toY) {
            ValueAnimator animator = ValueAnimator.ofFloat(ViewHelper.getTranslationY(mInterceptionLayout), toY).setDuration(200);
            animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    slideTo((float) animation.getAnimatedValue());
                }
            });
            animator.start();
        }
    }

    private float getAnchorYBottom() {
        return getScreenHeight() - mHeaderBarHeight;
    }

    private float getAnchorYImage() {
        return mImageView.getHeight();
    }

    private int getActionBarSize() {
        TypedValue typedValue = new TypedValue();
        int[] textSizeAttr = new int[]{R.attr.actionBarSize};
        int indexOfAttrTextSize = 0;
        TypedArray a = obtainStyledAttributes(typedValue.data, textSizeAttr);
        int actionBarSize = a.getDimensionPixelSize(indexOfAttrTextSize, -1);
        a.recycle();
        return actionBarSize;
    }

    private int getScreenHeight() {
        return findViewById(android.R.id.content).getHeight();
    }

    private void showFab() {
        if (!mFabIsShown && mFab != null) {
            ViewPropertyAnimator.animate(mFab).cancel();
            ViewPropertyAnimator.animate(mFab).scaleX(1).scaleY(1).setDuration(200).start();
            mFabIsShown = true;
        }
    }

    private void hideFab() {
        if (mFabIsShown && mFab != null) {
            ViewPropertyAnimator.animate(mFab).cancel();
            ViewPropertyAnimator.animate(mFab).scaleX(0).scaleY(0).setDuration(200).start();
            mFabIsShown = false;
        }
    }

    private void setBackgroundAlpha(View view, float alpha, int baseColor) {
        int a = Math.min(255, Math.max(0, (int) (alpha * 255))) << 24;
        int rgb = 0x00ffffff & baseColor;
        view.setBackgroundColor(a + rgb);
    }

}

On line 151 the visibility is set to gone.. Remove the line or set to visible.

Thanks!