Android：ViewPager高级使用

这里说的是ViewPager在页面切换的时候更改Item的样式：缩放、位置变化等等；本文罗列三种情况，具体如下：
1. 所有Item重叠，滑动时透明度变化，X、Y拉伸
代码如下：

public class PageTransformerOne implements ViewPager.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) {
            view.setAlpha(0);
        } else if (position <= 0) {
            view.setAlpha(1);
            view.setTranslationX(0);
            view.setScaleX(1);
            view.setScaleY(1);
        } else if (position <= 1) {
            view.setAlpha(1 - position);
            view.setTranslationX(pageWidth * -position);
            float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)
                    * (1 - Math.abs(position));
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
        } else {
            view.setAlpha(0);
        }
    }
}

运行效果：

第一种情况.png

2. 所有Item横向排列，滑动时透明度变化，X、Y拉伸
代码如下：

public class PageTransformerTwo implements ViewPager.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) {
            view.setAlpha(0);
        } else if (position <= 1) {
            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);
            }
            view.setScaleX(scaleFactor);
            view.setScaleY(scaleFactor);
            view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)
                    / (1 - MIN_SCALE) * (1 - MIN_ALPHA));
        } else {
            view.setAlpha(0);
        }
    }
}

滑动效果：

第二种情况.png

3. （类似于画廊的效果）所有Item横向排列，滑动时透明度变化，X、Y拉伸

public class PageTransformerThree implements ViewPager.PageTransformer {
    private float MIN_SCALE = 0.5f;
    @SuppressLint("NewApi")
    public void transformPage(View view, float position) {
        int pageWidth = view.getWidth();
        Log.d("123",position+"  viewpager");
        if (position < -1) {
            position = -1;
        } else if (position > 1) {
            position = 1;
        }
        view.setTranslationX(0);
        float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)
                * (1 - Math.abs(position));
        view.setScaleX(scaleFactor);
        view.setScaleY(scaleFactor);
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.KITKAT) {
            view.getParent().requestLayout();
        }
    }
}

滑动效果，也可以在屏幕上同时显示多个：

第三中情况.png