Android -- ViewPager切换动画，PageTransformer

transformPage(View view, float position)                                         

view就是滑动中的那个view，position这里是float类型，是当前滑动状态的一个表示，比如当滑动到正全屏时，position是0，如果前一页和下一页基本各在屏幕占一半时，前一页的position是-0.5，后一页的posiotn是0.5（是-0.5还是0.5要看当前的view是前面那一页的view还是后面那一页的），所以根据position的值我们就可以自行设置需要的alpha，x/y信息，就是可以用setAlpha()、setTranslationX()或setSaleY()来自定义切换动画。

Google官方提供动画效果                                                            

public class DepthPageTransformer implements PageTransformer {
    private static float MIN_SCALE = 0.75f;
 
    @SuppressLint("NewApi")
    @Override
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        if (position < -1) { // [-Infinity,-1)
                                // This page is way off-screen to the left.
            view.setAlpha(0);
        } else if (position <= 0) { // [-1,0]
                                    // Use the default slide transition when
                                    // moving to the left page
            view.setAlpha(1);
            view.setTranslationX(0);
            view.setScaleX(1);
            view.setScaleY(1);
        } else if (position <= 1) { // (0,1]
                                    // Fade the page out.
            view.setAlpha(1 - position);
            // Counteract the default slide transition
            view.setTranslationX(pageWidth * -position);
            // Scale the page down (between MIN_SCALE and 1)
            float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)
                    * (1 - Math.abs(position));
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
        } else { // (1,+Infinity]
                    // This page is way off-screen to the right.
            view.setAlpha(0);
         }
    }
}

public class ZoomOutPageTransformer implements PageTransformer {
    private static float MIN_SCALE = 0.85f;
 
    private static float MIN_ALPHA = 0.5f;
 
    @Override
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        int pageHeight = view.getHeight();
 
        if (position < -1) { // [-Infinity,-1)
                                // This page is way off-screen to the left.
            view.setAlpha(0);
        } else if (position <= 1) { // [-1,1]
                                    // Modify the default slide transition to
                                    // shrink the page as well
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0) {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }
            // Scale the page down (between MIN_SCALE and 1)
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
            // Fade the page relative to its size.
            view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
                    / (1 - MIN_SCALE) * (1 - MIN_ALPHA));
        } else { // (1,+Infinity]
                    // This page is way off-screen to the right.
            view.setAlpha(0);
        }
    }

使用                                                                                   

ViewPager mPager = (ViewPager) findViewById(R.id.pager);  
mPager.setPageTransformer(true, new DepthPageTransformer());

我是天王盖地虎的分割线                                                             

viewpager系列：

viewpager背景图渐变效果：Android -- ViewPager滑动背景渐变

viewpager+fragment：Android -- ViewPager、Fragment、状态保存、通信