ViewPager切换动画——PageTransformer

官方示例地址：
http://developer.android.com/training/animation/screen-slide.html

ViewPager的方法：

setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer)// 用于设置ViewPager切换时的动画效果

官方给出了两种效果实例：

一、DepthPageTransformer

public class DepthPageTransformer implements ViewPager.PageTransformer {  
    private static final float MIN_SCALE = 0.75f;  

    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);  
        }  
    }  
}

viewpager使用

mViewPager.setPageTransformer(true, new DepthPageTransformer());

效果图

二、ZoomOutPageTransformer

public class ZoomOutPageTransformer implements ViewPager.PageTransformer {  
    private static final float MIN_SCALE = 0.85f;  
    private static final float MIN_ALPHA = 0.5f;  

    @SuppressLint("NewApi")  
    public void transformPage(View view, float position)  
    {  
        int pageWidth = view.getWidth();  
        int pageHeight = view.getHeight();  

        Log.e("TAG", view + " , " + position + "");  

        if (position < -1)  
        { // [-Infinity,-1) 
            // This page is way off-screen to the left. 
            view.setAlpha(0);  

        } else if (position <= 1) //a页滑动至b页 ； a页从 0.0 -1 ；b页从1 ~ 0.0 
        { // [-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);  
        }  
    }  
}

viewpager使用

mViewPager.setPageTransformer(true, new ZoomOutPageTransformer());

还记得我上一篇博客 一屏显示多个ViewPager子item不？
http://blog.csdn.net/codenoodles/article/details/50991793
下面来给它加上切换动画：
直接上代码：

package com.upc.viewpagerGallery.View;

import android.support.v4.view.ViewPager;
import android.view.View;

/** * Created by Explorer on 2016/3/26. */
public class ZoomOutPageTransformer implements ViewPager.PageTransformer {

    private static final float MIN_SCALE = 0.9f;
    private static final float MIN_ALPHA = 0.5f;

    private static float defaultScale = 0.9f;

    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);
            view.setScaleX(defaultScale);
            view.setScaleY(defaultScale);
        } 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);
            view.setScaleX(defaultScale);
            view.setScaleY(defaultScale);
        }
    }
}

这里就不贴效果图了，你们能够在下一篇博客里看到效果。

说一下原理：
position范围不一样执行不一样的逻辑
- （无穷，-1）：左边view不可见
- [-1，0]：左边view可见
- (0，1]： 右边view可见
- (1,无穷):右边view不可见

咱们能够根据这个原理本身定制想要的效果。