JianShu/app/src/main/java/edu/whut/jianshu/Activity/MediaPlayerActivity.java

package edu.whut.jianshu.Activity;
import android.app.Activity;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.LayoutInflater;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.ImageView;
import android.widget.TextView;
import androidx.viewpager.widget.PagerAdapter;
import androidx.viewpager.widget.ViewPager;

import java.util.ArrayList;

import edu.whut.jianshu.R;

public class MediaPlayerActivity extends Activity implements View.OnClickListener{

    private ViewPager viewPager;
    private ArrayList<View> 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.pageview);
        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<View>();
        //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.weicheng).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;
        }
    }
}