Android实现轮播图片展示效果

<?xml version="1.0" encoding="utf-8"?>
<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 = {"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);
}
}