C# datatable 插入行，之前插入的为何不能保存？

前台

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

<!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:Button ID="Button1" runat="server" Text="添加第一行" OnClick="Button1_Click" />
            <asp:Button ID="Button2" runat="server" Text="添加第二行" OnClick="Button2_Click" />
            <asp:GridView ID="GridView1" runat="server" EnableModelValidation="True">
            </asp:GridView>

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

后台

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

public partial class inproduct : System.Web.UI.Page
{

    public DataTable dt = new DataTable();
    protected void Page_Load(object sender, EventArgs e)
    {

        DataColumn dc1 = new DataColumn("prizename", Type.GetType("System.String"));
        DataColumn dc2 = new DataColumn("point", Type.GetType("System.Int16"));
        DataColumn dc3 = new DataColumn("number", Type.GetType("System.Int16"));
        DataColumn dc4 = new DataColumn("totalpoint", Type.GetType("System.Int64"));
        DataColumn dc5 = new DataColumn("prizeid", Type.GetType("System.String"));
        dt.Columns.Add(dc1);
        dt.Columns.Add(dc2);
        dt.Columns.Add(dc3);
        dt.Columns.Add(dc4);
        dt.Columns.Add(dc5);
        DataRow dr = dt.NewRow();
        dr["prizename"] = "娃娃1";
        dr["point"] = 10;
        dr["number"] = 1;
        dr["totalpoint"] = 10;
        dr["prizeid"] = "001";
        dt.Rows.Add(dr);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }


    protected void Button1_Click(object sender, EventArgs e)
    {
        DataRow dr = dt.NewRow();
        dr["prizename"] = "娃娃2";
        dr["point"] = 20;
        dr["number"] = 2;
        dr["totalpoint"] = 20;
        dr["prizeid"] = "002";
        dt.Rows.Add(dr);
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }

    protected void Button2_Click(object sender, EventArgs e)
    {
        DataRow dr2 = dt.NewRow();
        dr2["prizename"] = "娃娃3";
        dr2["point"] = 30;
        dr2["number"] = 3;
        dr2["totalpoint"] = 30;
        dr2["prizeid"] = "003";
        dt.Rows.Add(dr2);

        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

你的代码中存在一个问题，即在每次添加新的行数据之后，你没有将DataTable对象保存到ViewState或Session中，因此在页面回发之后，DataTable对象中之前添加的数据会被清空。因此，如果你想要保存之前添加的数据，你需要在每次添加新的数据之后，将DataTable对象保存到ViewState或Session中。


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

public partial class inproduct : System.Web.UI.Page
{
    public DataTable dt;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            dt = new DataTable();
            DataColumn dc1 = new DataColumn("prizename", Type.GetType("System.String"));
            DataColumn dc2 = new DataColumn("point", Type.GetType("System.Int16"));
            DataColumn dc3 = new DataColumn("number", Type.GetType("System.Int16"));
            DataColumn dc4 = new DataColumn("totalpoint", Type.GetType("System.Int64"));
            DataColumn dc5 = new DataColumn("prizeid", Type.GetType("System.String"));
            dt.Columns.Add(dc1);
            dt.Columns.Add(dc2);
            dt.Columns.Add(dc3);
            dt.Columns.Add(dc4);
            dt.Columns.Add(dc5);
            DataRow dr = dt.NewRow();
            dr["prizename"] = "娃娃1";
            dr["point"] = 10;
            dr["number"] = 1;
            dr["totalpoint"] = 10;
            dr["prizeid"] = "001";
            dt.Rows.Add(dr);
            ViewState["dt"] = dt;
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
        else
        {
            dt = (DataTable)ViewState["dt"];
            GridView1.DataSource = dt;
            GridView1.DataBind();
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        dt = (DataTable)ViewState["dt"];
        DataRow dr = dt.NewRow();
        dr["prizename"] = "娃娃2";
        dr["point"] = 20;
        dr["number"] = 2;
        dr["totalpoint"] = 20;
        dr["prizeid"] = "002";
        dt.Rows.Add(dr);
        ViewState["dt"] = dt;
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }

    protected void Button2_Click(object sender, EventArgs e)
    {
        dt = (DataTable)ViewState["dt"];
        DataRow dr2 = dt.NewRow();
        dr2["prizename"] = "娃娃3";
        dr2["point"] = 30;
        dr2["number"] = 3;
        dr2["totalpoint"] = 30;
        dr2["prizeid"] = "003";
        dt.Rows.Add(dr2);
        ViewState["dt"] = dt;
        GridView1.DataSource = dt;
        GridView1.DataBind();
    }
}

在修改后的代码中，我们首先在Page_Load事件中判断页面是否是回发（Postback），如果不是回发，则创建一个新的DataTable对象，并向其中添加一行数据。然后，我们将DataTable对象保存到ViewState中。如果页面是回发，则从ViewState中获取之前保存的DataTable对象，并重新绑定GridView控件。

在Button1_Click和Button2_Click事件中，我们首先从ViewState中获取保存的DataTable对象，然后向其中添加新的行数据，并将DataTable对象重新保存到ViewState中。最后，我们重新绑定GridView控件，以显示最新的数据。

这样，你就可以在每次添加新的行数据之后，保存DataTable对象到ViewState中，从而确保之前添加的数据不会被清空。