ParallaxViewPager:ViewPager的视差背景效果

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源码:
import android.annotation.SuppressLint;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Rect;import android.graphics.drawable.BitmapDrawable;import android.graphics.drawable.Drawable;import android.support.v4.view.ViewPager;import android.util.AttributeSet;import android.util.Log;@SuppressLint("NewApi")public class ParallaxViewPager extends ViewPager {    public static final int FIT_WIDTH = 0;    public static final int FIT_HEIGHT = 1;    public static final float OVERLAP_FULL = 1f;    public static final float OVERLAP_HALF = 0.5f;    public static final float OVERLAP_QUARTER = 0.25f;    private static final float CORRECTION_PERCENTAGE = 0.01f;    public Bitmap bitmap;    private Rect source, destination;    private int scaleType;    private int chunkWidth;    private int projectedWidth;    private float overlap;    private OnPageChangeListener secondOnPageChangeListener;    public ParallaxViewPager(Context context) {        super(context);        init();    }    public ParallaxViewPager(Context context, AttributeSet attrs) {        super(context, attrs);        init();    }    private void init() {        source = new Rect();        destination = new Rect();        scaleType = FIT_HEIGHT;        overlap = OVERLAP_HALF;        setOnPageChangeListener(new OnPageChangeListener() {            @Override public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {                if (bitmap != null) {                    source.left = (int) Math.floor((position + positionOffset - CORRECTION_PERCENTAGE) * chunkWidth);                    source.right = (int) Math.ceil((position + positionOffset + CORRECTION_PERCENTAGE) * chunkWidth + projectedWidth);                    destination.left = (int) Math.floor((position + positionOffset - CORRECTION_PERCENTAGE) * getWidth());                    destination.right = (int) Math.ceil((position + positionOffset + 1 + CORRECTION_PERCENTAGE) * getWidth());                    invalidate();                }                if (secondOnPageChangeListener != null) {                    secondOnPageChangeListener.onPageScrolled(position, positionOffset, positionOffsetPixels);                }            }            @Override public void onPageSelected(int position) {                if (secondOnPageChangeListener != null) {                    secondOnPageChangeListener.onPageSelected(position);                }            }            @Override public void onPageScrollStateChanged(int state) {                if (secondOnPageChangeListener != null) {                    secondOnPageChangeListener.onPageScrollStateChanged(state);                }            }        });    }    @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) {        super.onSizeChanged(w, h, oldw, oldh);        destination.top = 0;        destination.bottom = h;        if (getAdapter() != null && bitmap != null)            calculateParallaxParameters();    }    private void calculateParallaxParameters() {        if (bitmap.getWidth() < getWidth() && bitmap.getWidth() < bitmap.getHeight() && scaleType == FIT_HEIGHT) {            Log.w(ParallaxViewPager.class.getName(), "Invalid bitmap bounds for the current device, parallax effect will not work.");        }        final float ratio = (float) getHeight() / bitmap.getHeight();        if (ratio != 1) {            switch (scaleType) {                case FIT_WIDTH:                    source.top = (int) ((bitmap.getHeight() - bitmap.getHeight() / ratio) / 2);                    source.bottom = bitmap.getHeight() - source.top;                    chunkWidth = (int) Math.ceil((float) bitmap.getWidth() / (float) getAdapter().getCount());                    projectedWidth = chunkWidth;                    break;                case FIT_HEIGHT:                default:                    source.top = 0;                    source.bottom = bitmap.getHeight();                    projectedWidth = (int) Math.ceil(getWidth() / ratio);                    chunkWidth = (int) Math.ceil((bitmap.getWidth() - projectedWidth) / (float) getAdapter().getCount() * overlap);                    break;            }        }    }    /**     * Sets the background from a resource file.     *     * @param resid     */    @Override public void setBackgroundResource(int resid) {        bitmap = BitmapFactory.decodeResource(getResources(), resid);    }    /**     * Sets the background from a Drawable.     *     * @param background     */    @Override public void setBackground(Drawable background) {        bitmap = ((BitmapDrawable) background).getBitmap();    }    /**     * Deprecated.     * Sets the background from a Drawable.     *     * @param background     */    @Override public void setBackgroundDrawable(Drawable background) {        bitmap = ((BitmapDrawable) background).getBitmap();    }    /**     * Sets the background from a bitmap.     *     * @param bitmap     * @return The ParallaxViewPager object itself.     */    public ParallaxViewPager setBackground(Bitmap bitmap) {        this.bitmap = bitmap;        return this;    }    /**     * Sets how the view should scale the background. The available choices are:     * <ul>     * <li>FIT_HEIGHT - the height of the image is resized to matched the height of the View, also stretching the width to keep the aspect ratio. The non-visible part of the bitmap is divided into equal parts, each of them sliding in at the proper position.</li>     * <li>FIT_WIDTH - the width of the background image is divided into equal chunks, each taking up the whole width of the screen.</li>     * </ul>     *     * @param scaleType     * @return     */    public ParallaxViewPager setScaleType(final int scaleType) {        if (scaleType != FIT_WIDTH && scaleType != FIT_HEIGHT)            throw new IllegalArgumentException("Illegal argument: scaleType must be FIT_WIDTH or FIT_HEIGHT");        this.scaleType = scaleType;        return this;    }    /**     * Sets the amount of overlapping with the setOverlapPercentage(final float percentage) method. This is a number between 0 and 1, the smaller it is, the slower is the background scrolling.     *     * @param percentage     * @return The ParallaxViewPager object itself.     */    public ParallaxViewPager setOverlapPercentage(final float percentage) {        if (percentage <= 0 || percentage >= 1)            throw new IllegalArgumentException("Illegal argument: percentage must be between 0 and 1");        overlap = percentage;        return this;    }    /**     * Recalculates the parameters of the parallax effect, useful after changes in runtime.     *     * @return The ParallaxViewPager object itself.     */    public ParallaxViewPager invalidateParallaxParameters() {        calculateParallaxParameters();        return this;    }    @Override protected void onDraw(Canvas canvas) {        if (bitmap != null)            canvas.drawBitmap(bitmap, source, destination, null);    }    public void addOnPageChangeListener(OnPageChangeListener listener) {        secondOnPageChangeListener = listener;    }}


使用:
在layout xml或者程序中创建了ParallaxViewPager之后,可以使用下面的方法来设置背景,或者也可以xml设置:
setBackgroundResource(int resid)setBackground(Drawable background) or setBackgroundDrawable(Drawable background)setBackground(Bitmap bitmap)

这就好了,你现在可以使用ParallaxViewPager的全部功能了。你可以修改背景的滚动效果来优化用户体验。你也可以使用setScaleType(final int scaleType)方法来配置视图的图像缩放方式。这个方法只能和FIT_HEIGHT搭配使用,从下面的参数中进行选择:

FIT_HEIGHT

表示缩放图像的高度以便适配视图的高度,同时缩放图像的宽度以便保持宽高比。bitmap的不可见部分被划分成相同的区域,每个区域插入到合适的位置。FIT_HEIGHT是默认值。

FIT_WIDTH

表示背景图像的宽度被划分成相同的块,每一块占满整个屏幕的宽度。这个模式不适用于视差效果,因为背景和视图的滚动速度一样。

你也可以使用setOverlapPercentage(final float percentage) 方法来设置重叠的程度。重叠程度值介于0到1之间,这个值越小背景就滚动地越慢,默认值是50%。
setContentView(R.layout.activity_main);final ParallaxViewPager parallaxViewPager = ((ParallaxViewPager) findViewById(R.id.parallaxviewpager));parallaxViewPager        .setOverlapPercentage(0.25f)        .setAdapter(new PagerAdapter()//...


<com.andraskindler.parallaxviewpager.ParallaxViewPager        xmlns:android="http://schemas.android.com/apk/res/android"        android:id="@+id/parallaxviewpager"        android:layout_width="match_parent"        android:background="@drawable/background"        android:layout_height="match_parent" />



https://github.com/andraskindler/parallaxviewpager

滑动Viewpager时背景颜色动态过渡变化效果
http://www.itlanbao.com/code/20150816/10000/100462.html
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