<&#63;xml version="1.0" encoding="utf-8"&#63;>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.a2_.MainActivity">

<android.support.v4.view.ViewPager
  android:id="@+id/vp"
  android:layout_width="match_parent"
  android:layout_height="250dp">
</android.support.v4.view.ViewPager>

<LinearLayout
  android:orientation="vertical"
  android:gravity="center"
  android:background="#66000000"
  android:layout_alignBottom="@id/vp"
  android:layout_width="match_parent"
  android:layout_height="50dp">

  <TextView
    android:id="@+id/desc"
    android:text="描述文本"
    android:textColor="#ffffff"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

  <LinearLayout
    android:id="@+id/layout_dot"
    android:orientation="horizontal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

  </LinearLayout>
</LinearLayout>
</RelativeLayout>

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<ImageView> 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 = {"為夢想堅持", "我相信我是黑馬", "黑馬公開課", "Google/IO", "輕松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);
  //給viewPager設置適配器
  viewPager.setAdapter(new MyPagerAdapter());
  //對viewPager設置監聽器
  viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {

    //當頁面滾動時觸發的時間
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }

    //當頁面被選中時觸發的方法
    @Override
    public void onPageSelected(int position) {
      //對position進行處理
      position = position % imageViews.size();
      //當頁面被選中的時候,改變描述文本
      tv_desc.setText(descs[position]);
      changeDots(position);
    }

    //當頁面狀態滾動狀態發生改變時觸發的事件
    @Override
    public void onPageScrollStateChanged(int state) {
      //當頁面空閑狀態被改變的時候
      if (state == viewPager.SCROLL_STATE_IDLE) {
        handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
      } else {
        handler.removeMessages(UPDATE_ITEM);
      }
    }
  });


  //初始化圖片
  initImage();
  //初始化文字下方的點
  initDot();
  //當加載頁面的時候,默認讓第一個文本加載出來
//    initDescFirst();

  //使兩邊都可以無限輪播
  viewPager.setCurrentItem(count / 2);
//頁面加載時更新
  upDataItem();
}

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

//選中對應的原點
private void changeDots(int position) {
  //先把所有的點恢復為白色
  for (int i = 0; i < layout_dot.getChildCount(); i++) {
    View view = layout_dot.getChildAt(i);
    view.setSelected(false);
  }
  //獲取當前被選中的條目 設置為選中狀態
  layout_dot.getChildAt(position).setSelected(true);

}

//初始化文字下方的點
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);
  }
}

//當加載頁面的時候,默認讓第一個文本加載出來
private void initDescFirst() {
  tv_desc.setText(descs[0]);
  changeDots(0);
}

//添加圖片,準備一個ImageView集合,用來交給instantiateItem添加到頁面
private void initImage() {
  for (int i = 0; i < imageResIds.length; i++) {
    //創建出ImageView對象
    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) {
    //判斷這個view是不是通過instantiateItem創建出來的
    return view == object;
  }

  //用來創建條目
  @Override
  public Object instantiateItem(ViewGroup container, int position) {
    position = position % imageResIds.length;
    //獲取條目
    ImageView imageView = imageViews.get(position);
    container.addView(imageView);
    return imageView;
  }

  //用來銷毀條目,,且最多會創建出三個條目,多出來的條目將會被銷毀
  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {

    //銷毀創建的條目
    container.removeView((View) object);
  }
}

@Override
protected void onStart() {
  super.onStart();
  //當頁面顯示的時候,更新輪播圖
  handler.sendEmptyMessageDelayed(UPDATE_ITEM, 3000);
}

@Override
protected void onStop() {
  super.onStop();
  //當頁面不可見時,停止更新
  handler.removeCallbacksAndMessages(null);
}
}