ParallaxScrollView.java

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2014 Nir Hartmann
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.fastbootmobile.encore.app.ui;

import java.util.ArrayList;

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

import com.fastbootmobile.encore.app.R;

public class ParallaxScrollView extends ObservableScrollView {

    private static final int DEFAULT_PARALLAX_VIEWS = 1;
    private static final float DEFAULT_INNER_PARALLAX_FACTOR = 1.9F;
    private static final float DEFAULT_PARALLAX_FACTOR = 1.9F;
    private int numOfParallaxViews = DEFAULT_PARALLAX_VIEWS;
    private float innerParallaxFactor = DEFAULT_PARALLAX_FACTOR;
    private float parallaxFactor = DEFAULT_PARALLAX_FACTOR;
    private ArrayList<ParallaxedView> parallaxedViews = new ArrayList<>();

    public ParallaxScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context, attrs);
    }

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

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

    protected void init(Context context, AttributeSet attrs) {
        TypedArray typeArray = context.obtainStyledAttributes(attrs, R.styleable.ParallaxScroll);
        this.parallaxFactor = typeArray.getFloat(R.styleable.ParallaxScroll_parallax_factor, DEFAULT_PARALLAX_FACTOR);
        this.innerParallaxFactor = typeArray.getFloat(R.styleable.ParallaxScroll_inner_parallax_factor, DEFAULT_INNER_PARALLAX_FACTOR);
        this.numOfParallaxViews = typeArray.getInt(R.styleable.ParallaxScroll_parallax_views_num, DEFAULT_PARALLAX_VIEWS);
        typeArray.recycle();
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        makeViewsParallax();
    }

    private void makeViewsParallax() {
        if (getChildCount() > 0 && getChildAt(0) instanceof ViewGroup) {
            ViewGroup viewsHolder = (ViewGroup) getChildAt(0);
            int numOfParallaxViews = Math.min(this.numOfParallaxViews, viewsHolder.getChildCount());
            for (int i = 0; i < numOfParallaxViews; i++) {
                ParallaxedView parallaxedView = new ScrollViewParallaxedItem(viewsHolder.getChildAt(i));
                parallaxedViews.add(parallaxedView);
            }
        }
    }

    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        float factor = parallaxFactor;
        for (ParallaxedView parallaxedView : parallaxedViews) {
            parallaxedView.setOffset((float) t / factor);
            factor *= innerParallaxFactor;
        }
    }

    protected class ScrollViewParallaxedItem extends ParallaxedView {

        public ScrollViewParallaxedItem(View view) {
            super(view);
        }

        @Override
        protected void translatePreICS(View view, float offset) {
            view.offsetTopAndBottom((int) offset - lastOffset);
            lastOffset = (int) offset;
        }
    }
}