FastScrollExpandableListView.java

/*
 * @copyright 2012 Philip Warner
 * @license GNU General Public License
 * 
 * This file is part of Book Catalogue.
 *
 * Book Catalogue is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Book Catalogue is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Book Catalogue.  If not, see <http://www.gnu.org/licenses/>.
 */

package com.eleybourn.bookcatalogue.widgets;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.AbsListView;
import android.widget.ExpandableListView;

/**
 * Subclass of ExpandableListView that uses a local implementation of FastScroller to bypass
 * the deficiencies in the original Android version. See fastScroller.java for a discussion.
 * 
 * We need to subclass ExpandableListView because we need access to events that are only provided
 * by the subclass.
 * 
 * @author Philip Warner
 */
public class FastScrollExpandableListView extends ExpandableListView {

	/** Active scroller, if any */
	FastScroller mScroller = null;
	
	public FastScrollExpandableListView(Context context ) {
		super(context);
	}
	public FastScrollExpandableListView(Context context, AttributeSet attrs ) {
		super(context, attrs);
	}
	public FastScrollExpandableListView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
	}

	private OnScrollListener mOnScrollListener = null;
	@Override
	public void setOnScrollListener(OnScrollListener listener) {
		mOnScrollListener = listener;
	}

	private OnScrollListener mOnScrollDispatcher = new OnScrollListener(){
		@Override
		public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
			if (mScroller != null)
				mScroller.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
			if (mOnScrollListener != null)
				mOnScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount);
		}

		@Override
		public void onScrollStateChanged(AbsListView view, int scrollState) {
			if (mOnScrollListener != null)
				mOnScrollListener.onScrollStateChanged(view, scrollState);
		};
	};

	{
		super.setOnScrollListener(mOnScrollDispatcher);
	}

	
	/**
	 * Called to create and start a new FastScroller if none already exists.
	 * 
	 * @param scroller
	 */
	private void initScroller() {
		if (mScroller != null)
			return;
		mScroller = new FastScroller(this.getContext(), this);
	}

	/**
	 * Pass to scroller if defined, otherwise perform default actions.
	 */
	@Override
	public boolean onInterceptTouchEvent(MotionEvent ev) {
		if (mScroller != null && mScroller.onInterceptTouchEvent(ev))
			return true;

		return super.onInterceptTouchEvent(ev);
	}
	/**
	 * Pass to scroller if defined, otherwise perform default actions.
	 */
	@Override
	protected void  onSizeChanged(int w, int h, int oldw, int oldh) {
		super.onSizeChanged(w, h, oldw, oldh);
		if (mScroller != null)
			mScroller.onSizeChanged(w, h, oldw, oldh);
	}
	/**
	 * Pass to scroller if defined, otherwise perform default actions.
	 */
	@Override
	public boolean onTouchEvent(MotionEvent ev) {
		if (mScroller != null && mScroller.onTouchEvent(ev))
			return true;

		return super.onTouchEvent(ev);
	}

	/**
	 * Send draw() to the scroller as well.
	 */
	@Override
	public void draw(Canvas canvas) {
		super.draw(canvas);
		if (mScroller != null)
			mScroller.draw(canvas);
	}

	/**
	 * Depending on 'enabled', either stop or start the scroller.
	 */
	@Override
	public void setFastScrollEnabled(boolean enabled) {
		if (!enabled) {
			if (mScroller != null) {
				mScroller.stop();
				mScroller = null;
			}
		} else {
			if (mScroller == null) {
				initScroller();
			}			
		}
	}
}