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
  }
}