get notified when Appbarlayout is expand and hide with scrolling offset and states.

ControllableAppBarLayout.java

package com.ajinkyabadve.mywatchlist.util.listeners;

/**
 * Copyright 2016 Ajinkya Badve
 * <p>
 * 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
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.graphics.Canvas;
import android.support.annotation.IntDef;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.util.AttributeSet;

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

import static com.ajinkyabadve.mywatchlist.util.listeners.ControllableAppBarLayout.ToolbarChange.COLLAPSE;
import static com.ajinkyabadve.mywatchlist.util.listeners.ControllableAppBarLayout.ToolbarChange.COLLAPSE_WITH_ANIMATION;
import static com.ajinkyabadve.mywatchlist.util.listeners.ControllableAppBarLayout.ToolbarChange.EXPAND;
import static com.ajinkyabadve.mywatchlist.util.listeners.ControllableAppBarLayout.ToolbarChange.EXPAND_WITH_ANIMATION;


public class ControllableAppBarLayout extends AppBarLayout
        implements AppBarLayout.OnOffsetChangedListener {
    private static final String TAG = ControllableAppBarLayout.class.getSimpleName();
    private AppBarLayout.Behavior mBehavior;
    private WeakReference<CoordinatorLayout> mParent;
    private int mQueuedChange = ToolbarChange.NONE;
    private boolean mAfterFirstDraw = false;
    private int state;
    private OnStateChangeListener onStateChangeListener;

    public ControllableAppBarLayout(Context context) {
        super(context);
    }

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

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        if (!(getLayoutParams() instanceof CoordinatorLayout.LayoutParams)
                || !(getParent() instanceof CoordinatorLayout)) {
            throw new IllegalStateException(
                    "ControllableAppBarLayout must be a direct child of CoordinatorLayout.");
        }
        mParent = new WeakReference<CoordinatorLayout>((CoordinatorLayout) getParent());
        addOnOffsetChangedListener(this);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mBehavior == null) {
            mBehavior = (Behavior) ((CoordinatorLayout.LayoutParams) getLayoutParams()).getBehavior();
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        if (r - l > 0 && b - t > 0 && mAfterFirstDraw && mQueuedChange != ToolbarChange.NONE) {
            analyzeQueuedChange();
        }
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        if (!mAfterFirstDraw) {
            mAfterFirstDraw = true;
            if (mQueuedChange != ToolbarChange.NONE) {
                analyzeQueuedChange();
            }
        }
    }

    private synchronized void analyzeQueuedChange() {
        switch (mQueuedChange) {
            case COLLAPSE:
                performCollapsingWithoutAnimation();
                break;
            case COLLAPSE_WITH_ANIMATION:
                performCollapsingWithAnimation();
                break;
            case EXPAND:
                performExpandingWithoutAnimation();
                break;
            case EXPAND_WITH_ANIMATION:
                performExpandingWithAnimation();
                break;
        }

        mQueuedChange = ToolbarChange.NONE;
    }

    public void collapseToolbar() {
        collapseToolbar(false);
    }

    public void collapseToolbar(boolean withAnimation) {
        mQueuedChange = withAnimation ? COLLAPSE_WITH_ANIMATION : COLLAPSE;
        requestLayout();
    }

    public void expandToolbar() {
        expandToolbar(false);
    }

    public void expandToolbar(boolean withAnimation) {
        mQueuedChange = withAnimation ? EXPAND_WITH_ANIMATION : EXPAND;
        requestLayout();
    }

    private void performCollapsingWithoutAnimation() {
        if (mParent.get() != null) {
            mBehavior.onNestedPreScroll(mParent.get(), this, null, 0, getHeight(), new int[]{0, 0});
        }
    }

    private void performCollapsingWithAnimation() {
        if (mParent.get() != null) {
            mBehavior.onNestedFling(mParent.get(), this, null, 0, getHeight(), true);
        }
    }

    private void performExpandingWithoutAnimation() {
        if (mParent.get() != null) {
            mBehavior.setTopAndBottomOffset(0);
        }
    }

    private void performExpandingWithAnimation() {
        if (mParent.get() != null) {
            mBehavior.onNestedFling(mParent.get(), this, null, 0, -getHeight() * 5, false);
        }
    }

    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int i) {
        if (i == 0) {
            if (onStateChangeListener != null && state != State.EXPANDED) {
                onStateChangeListener.onStateChange(State.EXPANDED, i);
            }
            state = State.EXPANDED;
        } else if (Math.abs(i) >= appBarLayout.getTotalScrollRange()) {
            if (onStateChangeListener != null && state != State.COLLAPSED) {
                onStateChangeListener.onStateChange(State.COLLAPSED, i);
            }
            state = State.COLLAPSED;
        } else {
            if (onStateChangeListener != null && state != State.IDLE) {
                onStateChangeListener.onStateChange(State.IDLE, i);
            }
            state = State.IDLE;
        }
    }

    public void setOnStateChangeListener(OnStateChangeListener listener) {
        this.onStateChangeListener = listener;
    }

    @State
    public int getState() {
        return state;
    }

    public interface OnStateChangeListener {
        void onStateChange(@State int toolbarChange, int offset);
    }

    @IntDef({State.COLLAPSED, State.EXPANDED, State.IDLE})
    @Retention(RetentionPolicy.SOURCE)
    public @interface State {
        int COLLAPSED = 0;
        int EXPANDED = 1;
        int IDLE = 2;
    }

    @IntDef({ToolbarChange.COLLAPSE, ToolbarChange.COLLAPSE_WITH_ANIMATION, ToolbarChange.EXPAND, ToolbarChange.EXPAND_WITH_ANIMATION, ToolbarChange.NONE})
    @Retention(RetentionPolicy.SOURCE)
    @interface ToolbarChange {
        int COLLAPSE = 3;
        int COLLAPSE_WITH_ANIMATION = 4;
        int EXPAND = 5;
        int EXPAND_WITH_ANIMATION = 6;
        int NONE = 7;
    }
}