从数据表中删除的行也从创建数据表会话变量中删除 [英] Rows removed from a datatable are also removed from the session variable that created the datatable

问题描述

我与会话变量中存储的数据表时注意到一些奇怪的行为。从一个从会话变量创建一个DataTable中删除一行似乎也修改会话变量如下证明。

I am noticing some strange behavior when working with datatables stored in session variables. Removing a row from a datatable that is created from a session variable appears to also modify the session variable as demonstrated below.

<asp:GridView ID="gvResults" runat="server" DataKeyNames="id">
<Columns>
    <asp:TemplateField ShowHeader="False">
        <ItemTemplate>
            <asp:Button ID="btnSelectUserToRemove" runat="server" CausesValidation="false" CommandName="Remove" Text="Select" CommandArgument='<%# Eval("id") %>' OnCommand="Command" />
        </ItemTemplate>
    </asp:TemplateField>
</Columns>
</asp:GridView>


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

public partial class Test : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DataTable dtResults = new DataTable();
            dtResults.Columns.Add("id");

            dtResults.Rows.Add();
            dtResults.Rows[0]["id"] = "1";
            dtResults.Rows.Add();
            dtResults.Rows[1]["id"] = "2";

            Session["id"] = dtResults;
            gvResults.DataSource = dtResults;
            gvResults.DataBind();
        }
    }

    protected void Command(object sender, CommandEventArgs e)
    {
        if (e.CommandName == "Remove")
        {
            DataTable dtTemp = (DataTable)Session["id"];
            for (Int32 i = 0; i < dtTemp.Rows.Count; i++)
            {
                if (e.CommandArgument.ToString() == dtTemp.Rows[i]["id"].ToString())
                {
                    dtTemp.Rows[i].Delete(); //Should just remove the row from the datatable.
                }
            }
            dtTemp.AcceptChanges();
        }
        DisplayData();
    }

    protected void DisplayData()
    {
        gvResults.DataSource = (DataTable)Session["id"];
        gvResults.DataBind(); //Should display both rows because I did not save the modified datatable back to this session variable.
    }
}

我不保存修改 dtTemp 数据表回会话[身份证] 变量。这是我的理解是应该有 dtTemp 1的行，因为一个行已被删除，而在 2行会话[身份证] 打电话时 DisplayData 。但是，只有一个行后显示在GridView DisplayData 运行。

I am not saving the modified dtTemp datatable back to the Session["id"] variable. It is my understanding that there should be 1 row in dtTemp, because one row was deleted, and 2 rows in Session["id"] when calling DisplayData. However, only one row is displayed in the gridview after DisplayData runs.

我希望有一个人在那里，可以解释为什么这种情况正在发生的一些情况。

I am hoping there is someone out there that can shed some light on why this is happening.

推荐答案

这是因为 dtTemp 和会话变量是对象引​​用都指向同一个对象。

It's because dtTemp and the session variable are object references that both point to the same object.

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