Using A Session Variable In ASP.Net Gridview

You can supply the Session variable value just before the Query is executed by SqlDataSource using the Selecting event of the datasource. Set this event in Markup using OnSelecting property.

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
    ConnectionString="<%$ ConnectionStrings:..... %>" 
    OnSelecting="SqlDataSource1_Selecting"
    SelectCommand="SELECT [Username], [Password], [CustomerName], [CustomerAddress], [Contact] FROM [Customers] WHERE ([Username] = @Username)">
    <SelectParameters>
        <asp:Parameter Name="Username" Type="String" />
    </SelectParameters>
</asp:SqlDataSource>

In the Selecting Event Handler, you do as below:

protected void SqlDataSource1_Selecting(object sender, SqlDataSourceSelectingEventArgs e) 
    { 
          if(Session["UserName"]!=null)
           {
           // do this only when Session Variable stores as a string the Username
           e.Command.Parameters["@Username"].Value = Session["UserName"];
           }
         else
           {
              // assign the default value if session variable is Null
              e.Command.Parameters["@Username"].Value ="DefaultValue";
            }

    }

In this event handler, you can access the command that’s about to be executed through the SqlDataSourceSelectingEventArgs.Command property, and modify its parameter values programmatically.

What I ended up doing was kind of similar to FlopScientist's answer. I found that the DataSource actually has an option for selecting a session variable which I did in the design view and it has the code below:

<asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="<%$ ConnectionStrings:..... %>" 

SelectCommand="SELECT [Password], [CustomerName], [CustomerAddress], [Contact], [Username] FROM [Customers] WHERE ([Username] = @Username)">



<SelectParameters>
            <asp:SessionParameter Name="Username" SessionField="mySessionVariable" Type="String" />


</SelectParameters>
</asp:SqlDataSource>

Session object in ASP.NET is one of the server side state maintenance variable.

More you can find here.

Session variable simply stores any value that you assign it to. And in simple words, you can access this variable on any other page, even if you created it on some other page.

so suppose on page1.aspx you did:

  Session["uniqueName"] = GetGridViewData(); //you can store anything.

where signature of GetGridViewData() is suppose like:

public DataTable GetGridViewData();

then on page2.aspx (or any other page), you can do this:

protected void Page_Load(object sender, EventArgs e)
{
   if(Session["uniqueName"]!=null)
   {
      //typecast it to your datastructure or whatever you assigned into it
      DataTable gridDataSource = (DataTable)Session["uniqueName"];

      //any custom logic you want to perform on gridDataSource
      gridView1.DataSource = gridDataSource;
      gridView.DataBind();
   }
}

Just make sure, you access the variable only after you have assigned/created earlier in the flow.