<?xml version="1.0" encoding="utf-8"?>







  

  

  

package com.example.a2_;

import android.os.Handler;
import android.os.Message;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;

import java.util.ArrayList;

public class MainActivity extends AppCompatActivity {
private static final int UPDATE_ITEM = 1;
private ArrayList imageViews = new ArrayList<>();
private int[] imageResIds = {R.mipmap.icon_1, R.mipmap.icon_2, R.mipmap.icon_3,
    R.mipmap.icon_4, R.mipmap.icon_5};

private String[] descs = {"为梦想坚持", "我相信我是黑马", "黑马公开课", "Google/IO", "轻松1w+"};
private ViewPager viewPager;
private TextView tv_desc;
private LinearLayout layout_dot;
private int count = 10000000;
private Handler handler = new Handler() {
  @Override
  public void handleMessage(Message msg) {
    switch (msg.what) {
      case UPDATE_ITEM:
        upDataItem();
        break;
    }
    super.handleMessage(msg);
  }
};

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  //初始化控件
  viewPager = (ViewPager) findViewById(R.id.vp);
  tv_desc = (TextView) findViewById(R.id.desc);
  layout_dot = (LinearLayout) findViewById(R.id.layout_dot);
  //给viewPager设置适配器
  viewPager.setAdapter(new MyPagerAdapter());
  //对viewPager设置监听器
  viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    //当页面滚动时触发的时间
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    //当页面被选中时触发的方法
    @Override
    public void onPageSelected(int position) {
      //对position进行处理
      position = position % imageViews.size();
      //当页面被选中的时候,改变描述文本
      tv_desc.setText(descs[position]);
      changeDots(position);
    }

    //当页面状态滚动状态发生改变时触发的事件
    @Override
    public void onPageScrollStateChanged(int state) {
      //当页面空闲状态被改变的时候
      if (state == viewPager.SCROLL_STATE_IDLE) {
        handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
      } else {
        handler.removeMessages(UPDATE_ITEM);
      }
    }
  });


  //初始化图片
  initImage();
  //初始化文字下方的点
  initDot();
  //当加载页面的时候,默认让第一个文本加载出来
//    initDescFirst();

  //使两边都可以无限轮播
  viewPager.setCurrentItem(count / 2);
//页面加载时更新
  upDataItem();
}

private void upDataItem() {
  int index = viewPager.getCurrentItem();
  viewPager.setCurrentItem(++index);
  handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
}

//选中对应的原点
private void changeDots(int position) {
  //先把所有的点恢复为白色
  for (int i = 0; i < layout_dot.getChildCount(); i++) {
    View view = layout_dot.getChildAt(i);
    view.setSelected(false);
  }
  //获取当前被选中的条目 设置为选中状态
  layout_dot.getChildAt(position).setSelected(true);

}

//初始化文字下方的点
private void initDot() {
  LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(10, 10);
  layoutParams.setMargins(4, 4, 4, 4);
  for (int i = 0; i < imageViews.size(); i++) {
    View view = new View(this);
    view.setBackgroundResource(R.drawable.seletor_dot);
    view.setLayoutParams(layoutParams);
    layout_dot.addView(view);
  }
}

//当加载页面的时候,默认让第一个文本加载出来
private void initDescFirst() {
  tv_desc.setText(descs[0]);
  changeDots(0);
}

//添加图片,准备一个ImageView集合,用来交给instantiateItem添加到页面
private void initImage() {
  for (int i = 0; i < imageResIds.length; i++) {
    //创建出ImageView对象
    ImageView imageView = new ImageView(getApplicationContext());
    imageView.setImageResource(imageResIds[i]);
    imageViews.add(imageView);
  }
}

private class MyPagerAdapter extends PagerAdapter {

  @Override
  public int getCount() {
    return count;
  }

  @Override
  public boolean isViewFromObject(View view, Object object) {
    //判断这个view是不是通过instantiateItem创建出来的
    return view == object;
  }

  //用来创建条目
  @Override
  public Object instantiateItem(ViewGroup container, int position) {
    position = position % imageResIds.length;
    //获取条目
    ImageView imageView = imageViews.get(position);
    container.addView(imageView);
    return imageView;
  }

  //用来销毁条目,,且最多会创建出三个条目,多出来的条目将会被销毁
  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {

    //销毁创建的条目
    container.removeView((View) object);
  }
}

@Override
protected void onStart() {
  super.onStart();
  //当页面显示的时候,更新轮播图
  handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
}

@Override
protected void onStop() {
  super.onStop();
  //当页面不可见时,停止更新
  handler.removeCallbacksAndMessages(null);
}
}