在Asp .net core 中不依赖插件实现分页

由于c#有强大的linq特性以及支持方法扩展，我们不需要什么第三方插件就能自己实现分页功能

1. 为了程序的可扩展性，分页参数可能会发生变化，不妨将分页参数如下封装起来

   public class PaginationResourceParameters
       {
           private const int MAXPAGESIZE = 50;
           private int _pageNumber = 1;
           public int PageNumber
           {
               get
               { return _pageNumber; }
               set
               {
                   if (value >= 1)
                   {
                       _pageNumber = value;
                   }
               }
           }
           private int _pageSize = 10;
           public int PageSize
           {
               get
               { return _pageSize; }
               set
               {
                   if (value >= 1)
                   {
                       _pageSize = (value > MAXPAGESIZE) ? MAXPAGESIZE : value;
                   }
               }
           }
       }
   

2. 在控制器的Action中传入分页参数

3. 调用repository时传入分页参数

4. 创建一个分页helper

   public class PaginationList<T> : List<T>
       {
           public int TotalPages { get; private set; }
           public int TotalCount { get; private set; }
           public int CurrentPage { get; set; }
           public bool HasPrevious => CurrentPage > 1;
           public bool HasNext => CurrentPage < TotalPages;
           public int PageSize { get; set; }
   
           public PaginationList(int totalcount, int currentPage, int pageSize, List<T> items)
           {
               CurrentPage = currentPage;
               PageSize = pageSize;
               TotalCount = totalcount;
               TotalPages = (int)Math.Ceiling(totalcount / (double)pageSize);
               AddRange(items);
           }
   
           public static async Task<PaginationList<T>> CreateAsync(
               int currentPage, int pageSize, IQueryable<T> result)
           {
               var totalCount = await result.CountAsync();
               var skip = (currentPage - 1) * pageSize;
               result = result.Skip(skip);
               result = result.Take(pageSize);
   
               var items = await result.ToListAsync();
   
               return new PaginationList<T>(totalCount, currentPage, pageSize, items);
           }
       }
   

5. 在repository中调用PaginationList实现分页

   return await PaginationList<TouristRoute>.CreateAsync(pageNumber, pageSize, res);