ParallaxToolbarScrollViewActivity.java

/*
 * Copyright 2014 Soichiro Kashima
 *
 * 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.
 */

package com.marshalchen.common.demoofui.observablescrollview;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;

import com.github.ksoichiro.android.observablescrollview.ObservableScrollView;
import com.github.ksoichiro.android.observablescrollview.ObservableScrollViewCallbacks;
import com.github.ksoichiro.android.observablescrollview.ScrollState;
import com.marshalchen.common.demoofui.R;
import com.nineoldandroids.view.ViewHelper;

public class ParallaxToolbarScrollViewActivity extends ActionBarActivity implements ObservableScrollViewCallbacks {

    private View mImageView;
    private View mToolbarView;
    private int mParallaxImageHeight;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.observable_scroll_view_activity_parallaxtoolbarscrollview);

        setSupportActionBar((Toolbar) findViewById(R.id.toolbar));

        mImageView = findViewById(R.id.image);
        mToolbarView = findViewById(R.id.toolbar);
        setBackgroundAlpha(mToolbarView, 0, getResources().getColor(R.color.primary));

        ObservableScrollView scrollView = (ObservableScrollView) findViewById(R.id.scroll);
        scrollView.setScrollViewCallbacks(this);

        mParallaxImageHeight = getResources().getDimensionPixelSize(R.dimen.parallax_image_height);
    }

    @Override
    public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) {
        int baseColor = getResources().getColor(R.color.primary);
        float alpha = 1 - (float) Math.max(0, mParallaxImageHeight - scrollY) / mParallaxImageHeight;
        setBackgroundAlpha(mToolbarView, alpha, baseColor);
        ViewHelper.setTranslationY(mImageView, scrollY / 2);
    }

    @Override
    public void onDownMotionEvent() {
    }

    @Override
    public void onUpOrCancelMotionEvent(ScrollState scrollState) {
    }

    private void setBackgroundAlpha(View view, float alpha, int baseColor) {
        int a = Math.min(255, Math.max(0, (int) (alpha * 255))) << 24;
        int rgb = 0x00ffffff & baseColor;
        view.setBackgroundColor(a + rgb);
    }
}