原文:
Android项目实战（四）：ViewPager切换动画（3.0版本以上有效果）
学习内容来自“慕课网”
一般APP进去之后都会有几张图片来导航，这里就学习怎么在这张图片切换的时候添加切换动画效果
先看布局文件
activity_main.layout
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/frameLayout1"
android:orientation="vertical">
</FrameLayout>
然后是java文件
mainactivity.java
1 package com.example.viewpage;
2
3 import java.util.ArrayList;
4 import java.util.List;
5
6 import android.os.Bundle;
7 import android.app.Activity;
8 import android.graphics.DashPathEffect;
9 import android.support.v4.view.PagerAdapter;
10 import android.support.v4.view.ViewPager;
11 import android.text.style.SuperscriptSpan;
12 import android.view.Menu;
13 import android.view.View;
14 import android.view.ViewGroup;
15 import android.view.Window;
16 import android.widget.ArrayAdapter;
17 import android.widget.ImageView;
18 import android.widget.ImageView.ScaleType;
19
20 public class MainActivity extends Activity {
21
22 private ViewPager mviewpager; //控件
23 private int[] mImgIds = new int[]{R.drawable.guide_image1,R.drawable.guide_image2,R.drawable.guide_image3};//初始化图片
24 private List<ImageView> mImages = new ArrayList<ImageView>();
25
26
27
28 @Override
29 protected void onCreate(Bundle savedInstanceState) {
30 super.onCreate(savedInstanceState);
31 requestWindowFeature(Window.FEATURE_NO_TITLE);
32 setContentView(R.layout.activity_main);
33
34 mviewpager = (ViewPager) findViewById(R.id.id_viewpager);
35 //为ViewPage切换添加动画效果(3.0以上版本才可以有效果)
36 mviewpager.setPageTransformer(true, new ZoomOutPageTransformer());
37
38 mviewpager.setAdapter(new PagerAdapter() {
39
40 @Override
41 public Object instantiateItem(View container, int position) {
42 ImageView imageview = new ImageView(MainActivity.this);
43 imageview.setImageResource(mImgIds[position]);
44 imageview.setScaleType(ScaleType.CENTER_CROP); //设置图片不变形
45 ((ViewGroup) container).addView(imageview);
46 mImages.add(imageview);
47 return imageview;
48 };
49 @Override
50 public void destroyItem(View container, int position, Object object) {
51 // TODO Auto-generated method stub
52
53 ((ViewPager) container).removeView(mImages.get(position));
54 }
55 public boolean isViewFromObject(View view, Object object) {
56 // TODO Auto-generated method stub
57 return view == object;
58 }
59
60 @Override
61 public int getCount() { //返回图片个数
62 // TODO Auto-generated method stub
63 return mImgIds.length;
64 }
65 });
66 }
67
68
69
70 }
这里代码很简单，主要就是一行代码控制切换效果 第36行mviewpager.setPageTransformer(true, new ZoomOutPageTransformer());
第二个参数就是切换效果，当然不是随便的参数
这些参数可以在http://wear.techbrood.com/training/animation/screen-slide.html网上查阅到
代码是给定的，只要复制代码，点击包粘贴就生成了相应的java文件
这里展示下几种效果：
1、ZoomOutPageTransformer（）
![]()
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1 public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
2 private static final float MIN_SCALE = 0.85f;
3 private static final float MIN_ALPHA = 0.5f;
4
5 public void transformPage(View view, float position) {
6 int pageWidth = view.getWidth();
7 int pageHeight = view.getHeight();
8
9 if (position < -1) { // [-Infinity,-1)
10 // This page is way off-screen to the left.
11 view.setAlpha(0);
12
13 } else if (position <= 1) { // [-1,1]
14 // Modify the default slide transition to shrink the page as well
15 float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
16 float vertMargin = pageHeight * (1 - scaleFactor) / 2;
17 float horzMargin = pageWidth * (1 - scaleFactor) / 2;
18 if (position < 0) {
19 view.setTranslationX(horzMargin - vertMargin / 2);
20 } else {
21 view.setTranslationX(-horzMargin + vertMargin / 2);
22 }
23
24 // Scale the page down (between MIN_SCALE and 1)
25 view.setScaleX(scaleFactor);
26 view.setScaleY(scaleFactor);
27
28 // Fade the page relative to its size.
29 view.setAlpha(MIN_ALPHA +
30 (scaleFactor - MIN_SCALE) /
31 (1 - MIN_SCALE) * (1 - MIN_ALPHA));
32
33 } else { // (1,+Infinity]
34 // This page is way off-screen to the right.
35 view.setAlpha(0);
36 }
37 }
38 }
View Code
效果图：
![]()
![]()
红色的为第一张，蓝色的为第二张，向左滑动显示蓝色。效果为两张图并行缩小滑动
2、DepthPageTransformer（）
![]()
![]()
1 public class DepthPageTransformer implements ViewPager.PageTransformer {
2 private static final float MIN_SCALE = 0.75f;
3
4 public void transformPage(View view, float position) {
5 int pageWidth = view.getWidth();
6
7 if (position < -1) { // [-Infinity,-1)
8 // This page is way off-screen to the left.
9 view.setAlpha(0);
10
11 } else if (position <= 0) { // [-1,0]
12 // Use the default slide transition when moving to the left page
13 view.setAlpha(1);
14 view.setTranslationX(0);
15 view.setScaleX(1);
16 view.setScaleY(1);
17
18 } else if (position <= 1) { // (0,1]
19 // Fade the page out.
20 view.setAlpha(1 - position);
21
22 // Counteract the default slide transition
23 view.setTranslationX(pageWidth * -position);
24
25 // Scale the page down (between MIN_SCALE and 1)
26 float scaleFactor = MIN_SCALE
27 + (1 - MIN_SCALE) * (1 - Math.abs(position));
28 view.setScaleX(scaleFactor);
29 view.setScaleY(scaleFactor);
30
31 } else { // (1,+Infinity]
32 // This page is way off-screen to the right.
33 view.setAlpha(0);
34 }
35 }
36 }
View Code
效果图：
![]()
![]()
![]()
红色的为第一张，蓝色的为第二张，向左滑动显示蓝色。效果为红色无变化向左滑动，蓝色由淡到深，由小到大占据屏幕
注意：添加DepthPageTransformer（）和ZoomOutPageTransformer（）java文件的时候 有两个错误 很容易 ctrl+1都能解决
更多动画类：
下载地址:
http://yunpan.cn/cFyjVgaeIFZ4e （提取码：ff5f）
