Android实现界面左右滑动切换功能

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package com.example.blacklotus.multimedia;
import android.app.Activity;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.VideoView;
import java.util.ArrayList;
public class MediaPlayerActivity extends Activity implements View.OnClickListener{
  private ViewPager viewPager;
  private ArrayList pageview;
  private TextView videoLayout;
  private TextView musicLayout;
  // 滚动条图片
  private ImageView scrollbar;
  // 滚动条初始偏移量
  private int offset = 0;
  // 当前页编号
  private int currIndex = 0;
  // 滚动条宽度
  private int bmpW;
  //一倍滚动量
  private int one;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_media_player);
    viewPager = (ViewPager) findViewById(R.id.viewPager);
    //查找布局文件用LayoutInflater.inflate
    LayoutInflater inflater =getLayoutInflater();
    View view1 = inflater.inflate(R.layout.video_player, null);
    View view2 = inflater.inflate(R.layout.media_player, null);
    videoLayout = (TextView)findViewById(R.id.videoLayout);
    musicLayout = (TextView)findViewById(R.id.musicLayout);
    scrollbar = (ImageView)findViewById(R.id.scrollbar);
    videoLayout.setOnClickListener(this);
    musicLayout.setOnClickListener(this);
    pageview =new ArrayList();
    //添加想要切换的界面
    pageview.add(view1);
    pageview.add(view2);
    //数据适配器
    PagerAdapter mPagerAdapter = new PagerAdapter(){
      @Override
      //获取当前窗体界面数
      public int getCount() {
        // TODO Auto-generated method stub
        return pageview.size();
      }
      @Override
      //判断是否由对象生成界面
      public boolean isViewFromObject(View arg0, Object arg1) {
        // TODO Auto-generated method stub
        return arg0==arg1;
      }
      //使从ViewGroup中移出当前View
      public void destroyItem(View arg0, int arg1, Object arg2) {
        ((ViewPager) arg0).removeView(pageview.get(arg1));
      }
      //返回一个对象，这个对象表明了PagerAdapter适配器选择哪个对象放在当前的ViewPager中
      public Object instantiateItem(View arg0, int arg1){
        ((ViewPager)arg0).addView(pageview.get(arg1));
        return pageview.get(arg1);
      }
    };
    //绑定适配器
    viewPager.setAdapter(mPagerAdapter);
    //设置viewPager的初始界面为第一个界面
    viewPager.setCurrentItem(0);
    //添加切换界面的监听器
    viewPager.addOnPageChangeListener(new MyOnPageChangeListener());
    // 获取滚动条的宽度
    bmpW = BitmapFactory.decodeResource(getResources(), R.drawable.scrollbar).getWidth();
    //为了获取屏幕宽度，新建一个DisplayMetrics对象
    DisplayMetrics displayMetrics = new DisplayMetrics();
    //将当前窗口的一些信息放在DisplayMetrics类中
    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    //得到屏幕的宽度
    int screenW = displayMetrics.widthPixels;
    //计算出滚动条初始的偏移量
    offset = (screenW / 2 - bmpW) / 2;
    //计算出切换一个界面时，滚动条的位移量
    One= offset * 2 + bmpW;
    Matrix matrix = new Matrix();
    matrix.postTranslate(offset, 0);
    //将滚动条的初始位置设置成与左边界间隔一个offset
    scrollbar.setImageMatrix(matrix);
  }
  public class MyOnPageChangeListener implements ViewPager.OnPageChangeListener {
    @Override
    public void onPageSelected(int arg0) {
      Animation animation = null;
      switch (arg0) {
        case 0:
            /**
             * TranslateAnimation的四个属性分别为
             * float fromXDelta 动画开始的点离当前View X坐标上的差值 
             * float toXDelta 动画结束的点离当前View X坐标上的差值 
             * float fromYDelta 动画开始的点离当前View Y坐标上的差值 
             * float toYDelta 动画开始的点离当前View Y坐标上的差值
            **/
            animation = new TranslateAnimation(one, 0, 0, 0);
          break;
        case 1:
            animation = new TranslateAnimation(offset, one, 0, 0);
          break;
      }
      //arg0为切换到的页的编码
      currIndex = arg0;
      // 将此属性设置为true可以使得图片停在动画结束时的位置
      animation.setFillAfter(true);
      //动画持续时间，单位为毫秒
      animation.setDuration(200);
      //滚动条开始动画
      scrollbar.startAnimation(animation);
    }
    @Override
    public void onPageScrolled(int arg0, float arg1, int arg2) {
    }
    @Override
    public void onPageScrollStateChanged(int arg0) {
    }
  }
  @Override
  public void onClick(View view){
     switch (view.getId()){
       case R.id.videoLayout:
         //点击"视频“时切换到第一页
         viewPager.setCurrentItem(0);
         break;
       case R.id.musicLayout:
         //点击“音乐”时切换的第二页
         viewPager.setCurrentItem(1);
         break;
     }
  }
}