Android ViewPager加载图片效果

目前项目中需要用到ViewPager加载图片，现在在此记录一下。

首先先看布局文件：activity_main.xml

<?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.fly.viewpagerbanner.MainActivity">
 <android.support.v4.view.ViewPager
  android:id="@+id/viewpager"
  android:layout_above="@+id/ll"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent" />
 <LinearLayout
  android:id="@+id/ll"
  android:layout_marginTop="10.0dip"
  android:orientation="horizontal"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_marginBottom="24.0dip"
  android:layout_alignParentBottom="true"
  android:layout_centerHorizontal="true"/>
</RelativeLayout>

MainActivity

package com.example.fly.viewpagerbanner;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener,View.OnClickListener {
 private ViewPager vp;
 private ViewPagerAdapter vpAdapter;
 private List<Map<String, Object>> data;
 private int lastValue = -1; // 是不是最后一张图片
 private ImageView[] dots; //底部小点图片
 private int currentIndex; //记录当前选中位置
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  //  Intent intent = new Intent();
//  intent.putStringArrayListExtra("GalleryPlusActivity",ArrayList<String>); // 怎么传递集合
  ArrayList<String> imageLists = getIntent().getStringArrayListExtra("GalleryPlusActivity"); // 动态获取展示图片的集合
  data = getData(imageLists);
  vp = (ViewPager) findViewById(R.id.viewpager);
  vpAdapter = new ViewPagerAdapter(data,this);
  vp.setAdapter(vpAdapter);
  vp.addOnPageChangeListener(this);
  initDots();//初始化底部小点
 }
 //这个方法长度是动态的，可以改成你从服务器获取的图片，这样数量就不确定啦
 public List<Map<String, Object>> getData(ArrayList<String> imageLists) {
  List<Map<String, Object>> mData = new ArrayList<>();
//  if (imageLists != null && imageLists.size() > 0) {
//   for (int i = 0; i < imageLists.size(); i++) {
//    Map<String, Object> map = new HashMap<>();
//    map.put("url", imageLists.get(i));
//    map.put("view", new ImageView(this));
//    mData.add(map);
//   }
//  }
  Map<String, Object> map = new HashMap<>();
  map.put("url", "http://huoche.7234.cn/images/jb51/va2zpt3i3rq");
  map.put("view", new ImageView(this));
  mData.add(map);
  Map<String, Object> map1 = new HashMap<>();
  map1.put("url", "http://huoche.7234.cn/images/jb51/1ck35mgwned");
  map1.put("view", new ImageView(this));
  mData.add(map1);
  Map<String, Object> map2 = new HashMap<>();
  map2.put("url", "http://download.pchome.net/wallpaper/pic-5041-8-240x320.jpg");
  map2.put("view", new ImageView(this));
  mData.add(map2);
  Map<String, Object> map3 = new HashMap<>();
  map3.put("url", "/file/imgs/upload/202206/06/e5e334jtGCu.jpg");
  map3.put("view", new ImageView(this));
  mData.add(map3);
  return mData;
 }
 private void initDots() {
  LinearLayout.LayoutParams mLayoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.WRAP_CONTENT, LinearLayout.LayoutParams.WRAP_CONTENT);
  mLayoutParams.setMargins(3, 0, 3, 0);
  LinearLayout ll = (LinearLayout) findViewById(R.id.ll);
  dots = new ImageView[data.size()];
  //循环取得小点图片
  for (int i = 0; i < data.size(); i++) {
   dots[i] = new ImageView(this);
   dots[i].setLayoutParams(mLayoutParams);
   dots[i].setBackgroundResource(R.drawable.dot);
   dots[i].setEnabled(true);//都设为灰色
   dots[i].setOnClickListener(this);
   dots[i].setTag(i);//设置位置tag，方便取出与当前位置对应
   ll.addView(dots[i]);
  }
  currentIndex = 0;
  dots[currentIndex].setEnabled(false);//设置为白色，即选中状态
 }
 private void setCurView(int position) { 
  if (position < 0 || position >= data.size()) {return;}
  vp.setCurrentItem(position);
 }
 private void setCurDot(int position) { 
  if (position < 0 || position > data.size() - 1 || currentIndex == position) {return;}
  dots[position].setEnabled(false);
  dots[currentIndex].setEnabled(true);
  currentIndex = position;
 }
 @Override //当前页面被滑动时调用
 public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
  lastValue = position;
 }
 @Override
 public void onPageSelected(int position) {     //当新的页面被选中时调用
  setCurDot(position); //设置底部小点选中状态
 }
 @Override
 public void onPageScrollStateChanged(int state) {   //当滑动状态改变时调用
  if(state == 0){
   if(lastValue == data.size()-1){
    Toast.makeText(this, "已经是最后一张了", Toast.LENGTH_SHORT).show();
   }
  }
 }
 @Override
 public void onClick(View v) {
  int position = (Integer)v.getTag();
  setCurView(position);
  setCurDot(position);
 }
}

ViewPagerAdapter

package com.example.fly.viewpagerbanner;
import android.content.Context;
import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import com.bumptech.glide.Glide;
import com.bumptech.glide.load.engine.DiskCacheStrategy;
import java.util.List;
import java.util.Map;
public class ViewPagerAdapter extends PagerAdapter {
 Context context;
 List<Map<String, Object>> viewLists;
 public ViewPagerAdapter(List<Map<String, Object>> lists, Context context) {
  this.viewLists = lists;
  this.context = context;
 }
 @Override
 public int getCount() {  //获得size
  return viewLists.size();
 }
 @Override
 public boolean isViewFromObject(View view, Object object) {
  return view == object;
 }
 @Override
 public void destroyItem(ViewGroup view, int position, Object object) { //销毁Item
  ImageView x = (ImageView) viewLists.get(position).get("view");
  x.setScaleType(ImageView.ScaleType.FIT_CENTER);
  view.removeView(x);
 }
 @Override
 public Object instantiateItem(ViewGroup view, int position){ //实例化Item
  ImageView imageView = (ImageView) viewLists.get(position).get("view");
  imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
  Glide.with(context)
    .load(viewLists.get(position).get("url").toString())
//    .placeholder(R.mipmap.new_default)
    .error(R.mipmap.ic_launcher)
    .diskCacheStrategy(DiskCacheStrategy.RESULT)
    .into(imageView);
  view.addView(imageView, 0);
  return viewLists.get(position).get("view");
 }
}

是不是很简单。
最后附上demo：http://xiazai.jb51.net/201701/yuanma/ViewPager(jb51.net).rar

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