viewpager的简单使用，以及ValueAnimator的用法示例

之前在网上看到一篇viewpager简单使用的例子程序，主要采用了上部标签button+中间指示作用的imageview+下部viewpager的结构，点击上部标签，或者滑动viewpager，均可以使中间的imageview产生滑动效果，但是由于程序不够完善，当改变imageview背景等时，不能够正确的显示我们期望的UI效果，因此我对此进行了优化，同时去掉原示例中使用的animation，转而采用valueanimator+imageview的matrix方法进行编码，解决了之前UI中体现的BUG,当然远远不能说满意，权当是对viewpager、valueanimator理解的入门示例。

注：以下编码对网上的示例程序多有借鉴，但是出处找不到了

 package com.example.testandroidviewpager;

 import java.util.ArrayList;
 import java.util.List;

 import android.animation.ValueAnimator;
 import android.app.Activity;
 import android.graphics.BitmapFactory;
 import android.graphics.Matrix;
 import android.os.Bundle;
 import android.os.Parcelable;
 import android.support.v4.view.PagerAdapter;
 import android.support.v4.view.ViewPager;
 import android.support.v4.view.ViewPager.OnPageChangeListener;
 import android.util.DisplayMetrics;
 import android.util.Log;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.Animation;
 import android.view.animation.BounceInterpolator;
 import android.view.animation.TranslateAnimation;
 import android.widget.ImageView;
 import android.widget.TextView;

 public class MainActivity extends Activity {

     private ViewPager mPager;//页卡内容
     private List<View> listViews; // Tab页面列表
     private ImageView cursor;// 动画图片
     private TextView t1, t2, t3;// 页卡头标
     private int offset = 0;// 动画图片偏移量
     private int currIndex = 0;// 当前页卡编号
     private int prevIndex = 0;// 移动前页卡编号
     private int bmpW;// 动画图片宽度
     private int screenW;//屏幕宽度，由于只是示例因此简单起见，直接使用屏幕宽度
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         InitTextView();
         InitImageView();
         InitViewPager();
     }

     /**
      * 初始化头标
      */
     private void InitTextView() {
         t1 = (TextView) findViewById(R.id.text1);
         t2 = (TextView) findViewById(R.id.text2);
         t3 = (TextView) findViewById(R.id.text3);

         t1.setOnClickListener(new MyOnClickListener(0));
         t2.setOnClickListener(new MyOnClickListener(1));
         t3.setOnClickListener(new MyOnClickListener(2));
     }

     /**
      * 头标点击监听
      */
     public class MyOnClickListener implements View.OnClickListener {
         private int index = 0;

         public MyOnClickListener(int i) {
             index = i;
         }

         @Override
         public void onClick(View v) {
             mPager.setCurrentItem(index);
         }
     };

     /**
      * 初始化ViewPager
      */
     private void InitViewPager() {
         mPager = (ViewPager) findViewById(R.id.vPager);
         listViews = new ArrayList<View>();
         LayoutInflater mInflater = getLayoutInflater();
         listViews.add(mInflater.inflate(R.layout.page0, null));
         listViews.add(mInflater.inflate(R.layout.page1, null));
         listViews.add(mInflater.inflate(R.layout.page2, null));
         mPager.setAdapter(new MyPagerAdapter(listViews));
         mPager.setCurrentItem(0);
         mPager.setOnPageChangeListener(new MyOnPageChangeListener());
     }

     /**
      * ViewPager适配器
      */
     public class MyPagerAdapter extends PagerAdapter {
         public List<View> mListViews;

         public MyPagerAdapter(List<View> mListViews) {
             this.mListViews = mListViews;
         }

         @Override
         public void destroyItem(View arg0, int arg1, Object arg2) {
             ((ViewPager) arg0).removeView(mListViews.get(arg1));
         }

         @Override
         public void finishUpdate(View arg0) {
         }

         @Override
         public int getCount() {
             return mListViews.size();
         }

         @Override
         public Object instantiateItem(View arg0, int arg1) {
             ((ViewPager) arg0).addView(mListViews.get(arg1), 0);
             return mListViews.get(arg1);
         }

         @Override
         public boolean isViewFromObject(View arg0, Object arg1) {
             Log.d("1202","view pager isViewFromObject --> return " + (arg0 == arg1));
             return arg0 == arg1;
         }

         @Override
         public void restoreState(Parcelable arg0, ClassLoader arg1) {
         }

         @Override
         public Parcelable saveState() {
             return null;
         }

         @Override
         public void startUpdate(View arg0) {
         }
     }

     /**
      * 初始化动画
      */
     private void InitImageView() {
         cursor = (ImageView) findViewById(R.id.cursor);
         bmpW = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher)
                 .getWidth();// 获取图片宽度
         DisplayMetrics dm = new DisplayMetrics();
         getWindowManager().getDefaultDisplay().getMetrics(dm);
         screenW = dm.widthPixels;// 获取分辨率宽度
         offset = (screenW / 3 - bmpW) / 2;// 计算偏移量
         Matrix matrix = new Matrix();
         matrix.postTranslate(offset, 0);
         cursor.setImageMatrix(matrix);// 设置动画初始位置
     }

     /**
      * 页卡切换监听
      */
     public class MyOnPageChangeListener implements OnPageChangeListener {

         int one = screenW / 3;// 页卡1 -> 页卡2 偏移量//==screenw/3
         int two = one * 2;// 页卡1 -> 页卡3 偏移量

         @Override
         public void onPageSelected(int arg0) {

             Animation animation = null;
             switch (arg0) {
             case 0:
                 if (currIndex == 1) {
                     animation = new TranslateAnimation(one, 0, 0, 0);
                 } else if (currIndex == 2) {
                     animation = new TranslateAnimation(two, 0, 0, 0);
                 }
                 break;
             case 1:
                 if (currIndex == 0) {
                     animation = new TranslateAnimation(0, one, 0, 0);
                 } else if (currIndex == 2) {
                     animation = new TranslateAnimation(two, one, 0, 0);
                 }
                 break;
             case 2:
                 if (currIndex == 0) {
                     animation = new TranslateAnimation(0, two, 0, 0);
                 } else if (currIndex == 1) {
                     animation = new TranslateAnimation(one, two, 0, 0);
                 }
                 break;
             }
             final Matrix matrix = new Matrix();
             prevIndex = currIndex;
             currIndex = arg0;

             ValueAnimator animator0 = ValueAnimator.ofFloat(0f, 1f);
             animator0.setDuration(300);
 //            animator0.setInterpolator(new BounceInterpolator());
             animator0.setInterpolator(new AccelerateInterpolator(2));
             animator0.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

                 @Override
                 public void onAnimationUpdate(ValueAnimator animation) {
                     Object o = animation.getAnimatedValue();
                     if(o != null){
                         float f = (Float)o;
                         Log.d("1201", "onAnimationUpdate f is " + f);
                         //prevIndex --> currIndex
                         matrix.reset();
                         int prevX = offset + one * prevIndex;
                         int currX = offset + one * currIndex;
                         int nowValue = (int) (prevX + f * (currX - prevX));
                         matrix.postTranslate(nowValue, 0);
                         cursor.setImageMatrix(matrix);
                     }
                 }
             });
             animator0.start();

             cursor.setImageMatrix(matrix);// 设置动画初始位置

 //            animation.setFillAfter(true);// True:图片停在动画结束位置
 //            animation.setDuration(300);
 //            cursor.startAnimation(animation);
         }

         @Override
         public void onPageScrolled(int arg0, float arg1, int arg2) {
         }

         @Override
         public void onPageScrollStateChanged(int arg0) {
         }
     }

 }

layout：activity_main.xml

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:umadsdk="http://schemas.android.com/apk/res/com.LoveBus"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:orientation="vertical" >

     <LinearLayout
         android:id="@+id/linearLayout1"
         android:layout_width="fill_parent"
         android:layout_height="100.0dip"
         android:background="#FFFFFF" >

         <TextView
             android:id="@+id/text1"
             android:layout_width="fill_parent"
             android:layout_height="fill_parent"
             android:layout_weight="1.0"
             android:gravity="center"
             android:text="页卡1"
             android:textColor="#000000"
             android:textSize="22.0dip" />

         <TextView
             android:id="@+id/text2"
             android:layout_width="fill_parent"
             android:layout_height="fill_parent"
             android:layout_weight="1.0"
             android:gravity="center"
             android:text="页卡2"
             android:textColor="#000000"
             android:textSize="22.0dip" />

         <TextView
             android:id="@+id/text3"
             android:layout_width="fill_parent"
             android:layout_height="fill_parent"
             android:layout_weight="1.0"
             android:gravity="center"
             android:text="页卡3"
             android:textColor="#000000"
             android:textSize="22.0dip" />
     </LinearLayout>

     <ImageView
         android:id="@+id/cursor"
         android:background="#333333"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:scaleType="matrix"
         android:src="@drawable/ic_launcher" />

     <android.support.v4.view.ViewPager
         android:id="@+id/vPager"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="center"
         android:layout_weight="1.0"
         android:background="#000000"
         android:flipInterval="30"
         android:persistentDrawingCache="animation" />

 </LinearLayout>

page0.xml
1 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="#330000"
     android:orientation="vertical" >

 </LinearLayout>

page1.xml

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="#003300"
     android:orientation="vertical" >

 </LinearLayout>

page2.xml

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="#000033"
     android:orientation="vertical" >

 </LinearLayout>

注意：位于界面中间的imageview，其scaletype一定要设置成为matrix。

原理：主要是使用valueanimator对matrix的

postTranslate()函数的参数进行了设置，然后不断更新imageview，使其具有动画效果。