Linq Pager 페이징

 

출처 : http://channel9.msdn.com/forums/TechOff/253890-Cool-Linq-Sample-0-Linq-Pager/

Each week till Linq launches I am going to post a Linq sample that shows off some Linq features.
This week how you make a pager function using linq. 
Paging is used to work with abstract idea of collection of containers that can hold something of a given type to lead users through a long list of items. A pager is something that can return a given container given some page size and which page the developer wants to return.
Linq can model this idea of pager in 1 line of code. Two IEnumerable<T> extension methods from System.Query namespace are used Skip and Take.
Skip(int) is called first this tells Enumerator to ignore a certain number of items represented as an int. The function assume the first page has a page number of 1 though you could certainly not decrement if you like to remain zero based. 
Take(int) constrains the number of items returned which we represent with the pageSize. 
public static IEnumerable<T> GetPage<T>
(int pageNumber, int pageSize, IEnumerable<T> list)
        {
                var output = list
                      .Skip((pageNumber - 1) * pageSize)
                      .Take(pageSize);
                return output;
        }
Here is a Windows Form Sample that uses the pager to iterate through a listing of DLLs in "C:\WINDOWS\Microsoft.NET\". This can be changed to prompt user for a value or a directory more appropriate to your testing OS folder structure.
The Window Form used consists of 4 controls:
Button id = Back
Button id = Next
Textbox id = Page
ListView id = FileView (change View to 'List')
Here is the code behind for the form:
using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace _PagingThroughFiles
{
    public partial class Form1 : Form
    {
        private IEnumerable<FileInfo> m_Files;
        private IEnumerable<FileInfo> m_Results;
        private int m_PageSize = 25;
        public Form1()
        {
            InitializeComponent();
            DirectoryInfo DI = new DirectoryInfo(@"C:\WINDOWS\Microsoft.NET\");
            m_Files =
                from file in DI.GetFiles("*", SearchOption.AllDirectories)
                where file.Extension == ".dll"
                orderby file.FullName
                select file;
            BindUI(1, m_PageSize);

        }
        private void BindUI(int pageNumber, int pageSize)
        {
            FileView.Items.Clear();

            m_Results = GetPage<FileInfo>(pageNumber, pageSize, m_Files);
            foreach (var file in m_Results)
            {
                FileView.Items.Add(new ListViewItem(file.FullName));
            }
            Page.Text = pageNumber.ToString();
            Back.Enabled = pageNumber != 1;
            Next.Enabled = ((pageNumber * pageSize) + 1) <= m_Files.Count();

        }

        private void Back_Click(object sender, EventArgs e)
        {
            BindUI(int.Parse(Page.Text) - 1, m_PageSize);

        }

        private void Next_Click(object sender, EventArgs e)
        {
            BindUI(int.Parse(Page.Text) + 1, m_PageSize);

        }
        public static IEnumerable<T> GetPage<T>
(int pageNumber, int pageSize, IEnumerable<T> list)
        {

            var output = list
                  .Skip((pageNumber - 1) * pageSize)
                  .Take(pageSize);
            return output;
        }

    }
}