前言

项目中我们可能会加载列表数据，点击列表进入图片浏览，一般情况就是朋友圈动态，点击九宫格图片，进入大图预览页面，但是如果假设我们产品经理要求将列表图片进行ViewPager左右滑动的话，那么我们就得进行分页加载了，因为列表数据可能存在成千条。

正题

我们知道ViewPager可以通过addOnPageChangeListener()方法监听我们滑动哪一页，那么设想我们知道我们的数据totalCount=1000，每页加载10条，当我滑动到10条的时候我们就需要去请求下一页数据，依次类推，我们的数据如果小于totalCount，并且我们滑动的条目正好是当前页的最后一条，那么我们就需要去加载更多。

-代码如下

package com.wj.viewpagertransfroms;

import android.app.assist.AssistStructure;
import android.content.Context;
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.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class ViewPagerMoreActivity extends AppCompatActivity {

    private ViewPager vp;

    private List<String> list = new ArrayList<>();

    private int limit = 10;

    private int maxListCount = 30;
    private MyAdapter adapter;


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

        vp = (ViewPager) findViewById(R.id.viewpager);

        for (int i = 1; i <= 10; i++) {
            list.add("第" + i + "页");
        }

        adapter = new MyAdapter(this);
        vp.setAdapter(adapter);
        vp.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
           
            }

            @Override
            public void onPageSelected(int position) {
                int page = position + 1;
                int size = list.size();
                if (page < maxListCount && page == size) {
                    //在这儿加载更多模拟网络请求
                    for (int i = size + 1; i <= size + 10; i++) {
                        if (i > maxListCount){
                            return;
                        }
                        list.add("第" + i + "页");
                    }
                    adapter.notifyDataSetChanged();
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }


    class MyAdapter extends PagerAdapter {

        private Context context;
        private LayoutInflater layoutInflater;

        public MyAdapter(Context context) {
            this.context = context;
            layoutInflater = LayoutInflater.from(context);
        }

        @Override
        public int getCount() {
            return list.size();
        }

        @Override
        public boolean isViewFromObject(View view, Object object) {
            return view == object;
        }

        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            View view = layoutInflater.inflate(R.layout.item_viewpager, null);
            TextView tv_page = (TextView) view.findViewById(R.id.tv_page);
            tv_page.setText(list.get(position));
            container.addView(view);
            return view;
        }

        @Override
        public void destroyItem(ViewGroup container, int position, Object object) {
            container.removeView((View) object);
        }
    }
}