ViewPager切换动画PageTransformer使用

Android从3.0开始，就添加了很多动画，ViewPager当然也不例外，相对于非常平庸的默认切换动画，Google给我们展示了两个动画例子：DepthPageTransformer和ZoomOutPageTransformer，实际上我们也可以通过实现ViewPager.PageTransformer来做出完全不同的切换动画效果。关键是要理解transformPage(View view, float position)的参数。view理所当然就是滑动中的那个view，position这里是float类型，不是平时理解的int位置，而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，而向左滑动，使得右边刚好有一部被进入屏幕时，position是1，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，所以根据position的值我们就可以自行设置需要的alpha，x/y信息。

下面，我们来看看Google官方提供的两种动画效果的代码，很简单，相信每个人看过之后，都能自己实现一种动画效果，

DepthPageTransformer：

 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);

         }
     }

 }

ZoomOutPageTransformer：

 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);
         }
     }
 }

有了这两种效果，我们在代码中设置一下就生效了：mPager.setPageTransformer(true, new DepthPageTransformer());

下面是效果图：第一张是 DepthPageTransformer效果，第二张是ZoomOutPageTransformer效果。

 

OK，最后奉上源代码：http://download.csdn.net/detail/weidi1989/6443601