Custom Android AppBarLayout$ScrollingViewBehavior: Prevent Toolbar from scrolling when RecyclerView doesn't have enough items to scroll.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright 2016 Alireza Eskandarpour Shoferi
  ~
  ~ 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.
  -->

<io.github.meness.testapplication.NotTouchableCoordinatorLayout
    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:fitsSystemWindows="false">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBarLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:fitsSystemWindows="true"
            app:layout_scrollFlags="scroll|enterAlways"
            app:title="@string/app_name"
            app:titleTextColor="@android:color/white">
        </android.support.v7.widget.Toolbar>

    </android.support.design.widget.AppBarLayout>

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:overScrollMode="never">

    </android.support.v7.widget.RecyclerView>
</io.github.meness.testapplication.NotTouchableCoordinatorLayout>

layout_sample_item.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright 2016 Alireza Eskandarpour Shoferi
  ~
  ~ 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.
  -->

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:orientation="vertical">

    <TextView
        android:id="@+id/name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="@android:style/TextAppearance.DeviceDefault.Large"/>
</LinearLayout>

MainActivity.java

/*
 * Copyright 2016 Alireza Eskandarpour Shoferi
 *
 * 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.
 */

import android.os.Bundle;
import android.support.design.widget.CoordinatorLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

import com.mikepenz.fastadapter.adapters.FastItemAdapter;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // init
        LinearLayoutManager layoutManager = new LinearLayoutManager(getApplicationContext());
        FastItemAdapter<SampleItem> adapter = new FastItemAdapter<>();
        RecyclerView rv = (RecyclerView) findViewById(R.id.rv);

        // set behavior to RecyclerView
        CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) rv.getLayoutParams();
        params.setBehavior(new ShouldScrolledBehavior(layoutManager, adapter));
        rv.setLayoutParams(params);

        rv.setLayoutManager(layoutManager);
        rv.setHasFixedSize(true);
        rv.setAdapter(adapter);

        for (int i = 1; i < 100; i++) {
            adapter.add(new SampleItem().setNumber(i));
        }
    }
}

NotTouchableCoordinatorLayout.java

/*
 * Copyright 2016 Alireza Eskandarpour Shoferi
 *
 * 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.
 */

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

/**
 * touching on CoordinatorLayout has disabled to only be scrolled while RecyclerView is scrolling
 */
public class NotTouchableCoordinatorLayout extends CoordinatorLayout {
    public NotTouchableCoordinatorLayout(Context context) {
        super(context);
    }

    public NotTouchableCoordinatorLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public NotTouchableCoordinatorLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return false;
    }
}

SampleItem.java

/*
 * Copyright 2016 Alireza Eskandarpour Shoferi
 *
 * 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.
 */

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;

import com.mikepenz.fastadapter.items.AbstractItem;

import java.util.List;

public class SampleItem extends AbstractItem<SampleItem, SampleItem.ViewHolder> {
    public int number;

    public SampleItem setNumber(int number) {
        this.number = number;
        return this;
    }

    @Override
    public int getType() {
        return 0;
    }

    @Override
    public int getLayoutRes() {
        return R.layout.layout_sample_item;
    }

    @Override
    public void bindView(ViewHolder holder, List payloads) {
        super.bindView(holder, payloads);

        holder.name.setText("Hello World " + number);
    }

    protected static class ViewHolder extends RecyclerView.ViewHolder {
        protected TextView name;

        public ViewHolder(View view) {
            super(view);
            this.name = (TextView) view.findViewById(R.id.name);
        }
    }
}

ShouldScrolledBehavior.java

/*
 * Copyright 2016 Alireza Eskandarpour Shoferi
 *
 * 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.
 */

import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.support.v7.widget.LinearLayoutManager;
import android.view.MotionEvent;
import android.view.View;

import com.mikepenz.fastadapter.adapters.FastItemAdapter;

/**
 * scroll when adapter's items are not completely visible. in other words,
 * toolbar is always visible till adapter's items are enough to be scrolled.
 */
public class ShouldScrolledBehavior extends AppBarLayout.ScrollingViewBehavior {
    private LinearLayoutManager mLayoutManager;
    private FastItemAdapter<SampleItem> mAdapter;

    public ShouldScrolledBehavior(LinearLayoutManager layoutManager, FastItemAdapter<SampleItem> adapter) {
        super();
        this.mLayoutManager = layoutManager;
        this.mAdapter = adapter;
    }

    @Override
    public boolean onInterceptTouchEvent(CoordinatorLayout parent, View child, MotionEvent ev) {
        return !shouldScrolled();
    }

    public boolean shouldScrolled() {
        // adapter has more items that not shown yet
        if (mLayoutManager.findLastCompletelyVisibleItemPosition() != mAdapter.getAdapterItemCount() - 1) {
            return true;
        }
        // last completely visible item is the last item in adapter but it may be occurred in 2 ways:
        // 1) all items are shown
        // 2) scrolled to the last item (implemented following)
        else if (mLayoutManager.findLastCompletelyVisibleItemPosition() == mAdapter.getAdapterItemCount() - 1 && mLayoutManager.findFirstCompletelyVisibleItemPosition() != 0) {
            return true;
        }
        return false;
    }
}