An extension of Android AppBarLayout, that allows to programatically change the CollapsibleToolbarLayout state and receive state changes (collapsed, expanded and idle)

ControllableAppBarLayout.java

package com.eatfirst.android.ui.custom;

/**
 * Copyright 2015 Bartosz Lipinski
 *
 * 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.graphics.Canvas;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.util.AttributeSet;
import java.lang.ref.WeakReference;

public class ControllableAppBarLayout extends AppBarLayout
    implements AppBarLayout.OnOffsetChangedListener {
  private AppBarLayout.Behavior mBehavior;
  private WeakReference<CoordinatorLayout> mParent;
  private ToolbarChange mQueuedChange = ToolbarChange.NONE;
  private boolean mAfterFirstDraw = false;
  private State 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 ? ToolbarChange.COLLAPSE_WITH_ANIMATION : ToolbarChange.COLLAPSE;
    requestLayout();
  }

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

  public void expandToolbar(boolean withAnimation) {
    mQueuedChange = withAnimation ? ToolbarChange.EXPAND_WITH_ANIMATION : ToolbarChange.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);
      }
      state = State.EXPANDED;
    } else if (Math.abs(i) >= appBarLayout.getTotalScrollRange()) {
      if (onStateChangeListener != null && state != State.COLLAPSED) {
        onStateChangeListener.onStateChange(State.COLLAPSED);
      }
      state = State.COLLAPSED;
    } else {
      if (onStateChangeListener != null && state != State.IDLE) {
        onStateChangeListener.onStateChange(State.IDLE);
      }
      state = State.IDLE;
    }
  }

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

  public State getState() {
    return state;
  }

  public interface OnStateChangeListener {
    void onStateChange(State toolbarChange);
  }

  public enum State {
    COLLAPSED,
    EXPANDED,
    IDLE
  }

  private enum ToolbarChange {
    COLLAPSE,
    COLLAPSE_WITH_ANIMATION,
    EXPAND,
    EXPAND_WITH_ANIMATION,
    NONE
  }
}

@maheshwarLigade maybe you can follow this example https://github.com/saulmm/CoordinatorBehaviorExample

Hi I really

Don't understand how to use this class, I receive an parse error, I don't know what I have to write in this line

ControllableAppBarLayout appBarLayout = // get the instance from your view

Maybe if you can do a little example with a simple Log.d using this class, I really appreciate

thank you very much.

How to know when it begins to expand?

Please use intDef instead of enums.
here is updated post

how to collapse to position,who can help