WebForm Application Viewstate 以及分页（功能性的知识点）

Application：

全局公共变量组

　　存放位置：服务器

　　特点：所有访问用户都是访问同一个变量，但只要服务器不停机，变量一直存在于服务器的内存中，不要使用循环大量的创建Application对象，可能会造

　　　　　成服务器崩溃。

　　生命周期：永久，只要服务器不停机

　　使用方法：与Session一样

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Viewstate:

用于记录页面的一些状态，就像人的病例，比如当执行提交后，网页可以保留一些已经输入的文本框而非清空

　　webform中微软已经给我们做好了这个对象，自带此功能。

webform中一共6个内置对象：Request  Response  Session  Cookie Application ViewState

___________________________________________________________________________________________________________________________常规表单提交：

普通HTML页面，在form表单中action属性可以设置提交到哪个服务端 method属性可以选择提交方式

<form action="Default4.aspx" method="get"></form>

　　可以通过此方法将纯HTML页面中的数据提交到某个服务端，再通过服务端对数据进行操作。

___________________________________________________________________________________________________________________________

分页功能：

　　为了用户查看以及页面加载速度，查看大量数据时需要进行分页操作，　

　　主要通过查询语句以及各种判断来实现

　　例：分页展示车辆信息管理

1.界面层

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <div>

            <asp:Repeater ID="Repeater1" runat="server">
                <HeaderTemplate>

                    <table style="width: 100%; text-align: center; ">
                        <thead>
                            <tr style="color: white;">
                                <%--<td>ids</td>--%>
                                <td>code</td>
                                <td>name</td>
                                <td>brand</td>
                                <td>time</td>
                                <td>oil</td>
                                <td>powers</td>
                                <td>exhaust</td>
                                <td>price</td>
                                <td>pic</td>
                            </tr>
                        </thead>
                        <tbody>
                </HeaderTemplate>

                <ItemTemplate>

                    <tr style="">
                        <%--<td><%#Eval("ids") %></td>--%>
                        <td><%#Eval("code") %></td>
                        <td><%#Eval("name") %></td>
                        <td><%#Eval("brand") %></td>
                        <td><%#Eval("time") %></td>
                        <td><%#Eval("oil") %></td>
                        <td><%#Eval("powers") %></td>
                        <td><%#Eval("exhaust") %></td>
                        <td><%#Eval("price") %></td>
                        <td><%#Eval("pic") %></td>
                    </tr>

                </ItemTemplate>
                <FooterTemplate>
                    </tbody>
            </table>
                </FooterTemplate>
            </asp:Repeater>

            当前第【<asp:Label ID="Label_NowPage" runat="server" Text="Label"></asp:Label>】页
            &nbsp;&nbsp;共【<asp:Label ID="Label_MaxPage" runat="server" Text="Label"></asp:Label>】页&nbsp;&nbsp;
            <asp:LinkButton ID="btn_first" runat="server">首页</asp:LinkButton>
            &nbsp;&nbsp;
            <asp:LinkButton ID="btn_prev" runat="server">上一页</asp:LinkButton>
            &nbsp;&nbsp;
            <asp:LinkButton ID="btn_next" runat="server">下一页</asp:LinkButton>
            &nbsp;&nbsp;
            <asp:LinkButton ID="btn_last" runat="server">末页</asp:LinkButton>
            &nbsp;&nbsp;
            <asp:DropDownList ID="DropDownList1" AutoPostBack="true" runat="server"></asp:DropDownList>
            <asp:Button ID="Button1" runat="server" Text="跳转" />

        </div>
    </form>
</body>
</html>

2.后台代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    int Count = 5; //每页显示条数

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Label_NowPage.Text = "1";
            Label_MaxPage.Text = MaxPageNumber().ToString();
            btn_prev.Enabled = false;
            btn_first.Enabled = false;

            Repeater1.DataSource = new CarData().Select(Count, 1);
            Repeater1.DataBind();

            int max = MaxPageNumber();
            DropDownList1.Items.Clear();
            for (int i = 1; i <= max; i++)
            {
                DropDownList1.Items.Add(new ListItem(i.ToString(), i.ToString()));
            }
        }

        DropDownList1.SelectedIndexChanged += Button1_Click;
        btn_first.Click += btn_first_Click;//首页按钮
        btn_prev.Click += btn_prev_Click;
        btn_next.Click += btn_next_Click;
        btn_last.Click += btn_last_Click;
        Button1.Click += Button1_Click;
    }

    void Button1_Click(object sender, EventArgs e)
    {
        //获取当前页，计算要看的下一页的页号
        int nextPage = Convert.ToInt32(DropDownList1.SelectedValue);

        //按照获取的页数绑定相应的数据
        Repeater1.DataSource = new CarData().Select(Count, nextPage);
        Repeater1.DataBind();

        //修改显示页数
        Label_NowPage.Text = nextPage.ToString();

        if (nextPage == 1)
        {
            btn_first.Enabled = false;
            btn_prev.Enabled = false;
            btn_next.Enabled = true;
            btn_last.Enabled = true;
        }
        else if (nextPage == MaxPageNumber())
        {
            btn_first.Enabled = true;
            btn_prev.Enabled = true;
            btn_next.Enabled = false;
            btn_last.Enabled = false;
        }
        else
        {
            btn_first.Enabled = true;
            btn_prev.Enabled = true;
            btn_next.Enabled = true;
            btn_last.Enabled = true;
        }
    }

    void btn_first_Click(object sender, EventArgs e)
    {
        //按照获取的页数绑定相应的数据
        Repeater1.DataSource = new CarData().Select(Count, 1);
        Repeater1.DataBind();

        //修改显示页数
        Label_NowPage.Text = "1";

        btn_first.Enabled = false;
        btn_prev.Enabled = false;
        btn_next.Enabled = true;
        btn_last.Enabled = true;
    }

    void btn_prev_Click(object sender, EventArgs e)
    {
        //获取当前页，计算要看的下一页的页号
        int nextPage = Convert.ToInt32(Label_NowPage.Text) - 1;

        //按照获取的页数绑定相应的数据
        Repeater1.DataSource = new CarData().Select(Count, nextPage);
        Repeater1.DataBind();

        //修改显示页数
        Label_NowPage.Text = nextPage.ToString();

        if (nextPage <= 1)
        {
            btn_first.Enabled = false;
            btn_prev.Enabled = false;
        }
        btn_next.Enabled = true;
        btn_last.Enabled = true;
    }

    void btn_next_Click(object sender, EventArgs e)
    {
        //获取当前页，计算要看的下一页的页号
        int nextPage = Convert.ToInt32(Label_NowPage.Text) + 1;

        ////判断是否有下一页
        //if (nextPage > MaxPageNumber())
        //{
        //    return;
        //}

        //按照获取的页数绑定相应的数据
        Repeater1.DataSource = new CarData().Select(Count, nextPage);
        Repeater1.DataBind();

        //修改显示页数
        Label_NowPage.Text = nextPage.ToString();

        if (nextPage >= MaxPageNumber())
        {
            btn_next.Enabled = false;
            btn_last.Enabled = false;
        }
        btn_prev.Enabled = true;
        btn_first.Enabled = true;
    }

    void btn_last_Click(object sender, EventArgs e)
    {
        int hehe = MaxPageNumber();

        //按照获取的页数绑定相应的数据
        Repeater1.DataSource = new CarData().Select(Count, hehe);
        Repeater1.DataBind();

        //修改显示页数
        Label_NowPage.Text = hehe.ToString();

        btn_prev.Enabled = true;
        btn_first.Enabled = true;
        btn_next.Enabled = false;
        btn_last.Enabled = false;
    }

    public int MaxPageNumber()
    {
        List<Car> clist = new CarData().Select();

        double end2 = Math.Ceiling(clist.Count / (Count * 1.0));

        int end = Convert.ToInt32(end2);

        return end;
    }

}
3，数据访问类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data.SqlClient;

/// <summary>
/// CarData 的摘要说明
/// </summary>
public class CarData
{
    SqlConnection conn = null;
    SqlCommand cmd = null;
    public CarData()
    {
        conn = new SqlConnection("server=.;database=mydb;user=sa;pwd=123");
        cmd = conn.CreateCommand();
    }

    public List<Car> Select()
    {
        List<Car> clist = new List<Car>();

        cmd.CommandText = "select *from car";
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader();

        if (dr.HasRows)
        {
            while (dr.Read())
            {
                Car c = new Car();
                //c.Ids = Convert.ToInt32(dr[0]);
                c.Code = dr[0].ToString();
                c.Name = dr[1].ToString();
                c.Brand = dr[2].ToString();
                c.Time = Convert.ToDateTime(dr[3]);
                c.Oil = Convert.ToDecimal(dr[4]);
                c.Powers = Convert.ToInt32(dr[5]);
                c.Exhaust = Convert.ToInt32(dr[6]);
                c.Price = Convert.ToDecimal(dr[7]);
                c.Pic = dr[8].ToString();

                clist.Add(c);
            }
        }

        conn.Close();
        return clist;
    }

    public List<Car> Select(int count, int NowPage)
    {
        List<Car> clist = new List<Car>();

        cmd.CommandText = "select top " + count + " *from car where Code not in(select top " + ((NowPage - 1) * count) + " Code from car)";
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader();

        if (dr.HasRows)
        {
            while (dr.Read())
            {
                Car c = new Car();
                //c.Ids = Convert.ToInt32(dr[0]);
                c.Code = dr[0].ToString();
                c.Name = dr[1].ToString();
                c.Brand = dr[2].ToString();
                c.Time = Convert.ToDateTime(dr[3]);
                c.Oil = Convert.ToDecimal(dr[4]);
                c.Powers = Convert.ToInt32(dr[5]);
                c.Exhaust = Convert.ToInt32(dr[6]);
                c.Price = Convert.ToDecimal(dr[7]);
                c.Pic = dr[8].ToString();

                clist.Add(c);
            }
        }

        conn.Close();
        return clist;
    }
}
4.最后呈现的效果如图所示：