In this article I will explain with an example, how to DataTable as a temporary storage table in ASP.Net for storing the records that we need for processing in ViewState or Session variables.
The concept is to create a dynamic DataTable, store some values in it and then keep the DataTable either in ViewState or Session depending on whether you want it only on the page or throughout the application respectively.
In order to illustrate this concept, I will make use an ASP.Net GridView control on which I’ll perform Edit and Update operations and the save the updated data with the temporary DataTable.
 
 

HTML Markup

The following HTML Markup consists of:
GridView – For displaying data.

Columns

The GridView consists of two BoundField column and TemplateField columns.
TemplateField – The TemplateField column consists of ItemTemplate and EditItemTemplate.
ItemTemplate – It consists of a LinkButton for edit column.
EditItemTemplate – It consists of two LinkButton for update and cancel column.
<asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false" OnRowEditing="OnRowEditing">
    <Columns>
        <asp:BoundField DataField="Name" HeaderText="Name" ItemStyle-Width="150" />
        <asp:BoundField DataField="Country" HeaderText="Country" ItemStyle-Width="150" />
        <asp:TemplateField>
            <ItemTemplate>
                <asp:LinkButton Text="Edit" runat="server" CommandName="Edit" />
            </ItemTemplate>
            <EditItemTemplate>
                <asp:LinkButton Text="Update" runat="server" OnClick="OnUpdate" />
                <asp:LinkButton Text="Cancel" runat="server" OnClick="OnCancel" />
            </EditItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
 
 

Namespaces

You will need to import the following namespace.
C#
using System.Data;
 
VB.Net
Imports System.Data
 
 

Populating the GridView with a dynamic temporary DataTable

Inside the Page_Load event handler, an object of DataTable is created.
Then, three columns are added to the DataTable Columns collection using the AddRange method.
An Array of objects of type DataColumn is specified which will hold the name and the optional parameter Data Type i.e. the Type of the column.
Once the schema is ready i.e. all the columns are defined, some rows have been added using the Rows.Add method.
Finally, the dynamic temporary DataTable is saved in a ViewState variable and finally it is used to populate the GridView control.
Note: You can also make use of Session variable if you need to use the temporary DataTable across the whole application.
 
C#
protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] {
            new DataColumn("Id"),
            new DataColumn("Name"),
            new DataColumn("Country") });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        ViewState["dt"] = dt;
        this.BindGrid();
    }
}
 
protected void BindGrid()
{
    gvCustomers.DataSource = ViewState["dt"]as DataTable;
    gvCustomers.DataBind();
}
 
VB.Net
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim dt As New DataTable()
        dt.Columns.AddRange(New DataColumn(2) {
                            New DataColumn("Id"),
                            New DataColumn("Name"),
                            New DataColumn("Country")})
        dt.Rows.Add(1, "John Hammond", "United States")
        dt.Rows.Add(2, "Mudassar Khan", "India")
        dt.Rows.Add(3, "Suzanne Mathews", "France")
        dt.Rows.Add(4, "Robert Schidner", "Russia")
        ViewState("dt") = dt
        Me.BindGrid()
    End If
End Sub
 
Protected Sub BindGrid()
     gvCustomers.DataSource = TryCast(ViewState("dt"), DataTable)
    gvCustomers.DataBind()
End Sub
 
Using DataTable as Temporary storage table in ASP.Net
 
 

Edit

When the Edit Button is clicked, the GridView’s OnRowEditing event handler is triggered, where the EditIndex of the GridView is updated with the Row Index of the GridView Row to be edited.
C#
protected void OnRowEditing(object sender, GridViewEditEventArgs e)
{
    gvCustomers.EditIndex = e.NewEditIndex;
    this.BindGrid();
}
 
VB.Net
Protected Sub OnRowEditing(sender As Object, e As GridViewEditEventArgs)
    gvCustomers.EditIndex = e.NewEditIndex
    Me.BindGrid()
End Sub
 
Using DataTable as Temporary storage table in ASP.Net
 
 

GridView Row Update and Cancel Edit Events

When the Update Button is clicked, the GridView’s OnUpdate event handler is triggered.
Inside the OnUpdate event handler, the temporary DataTable is fetched back from the ViewState variable and then the row to be updated is identified using the RowIndex of the GridView Row whose Update button was clicked.
Then the values to be updated are fetched from the TextBoxes and are assigned to the respective columns of the DataTable Row.
Finally, the temporary DataTable is saved back in ViewState and the GridView is again populated with the updated temporary DataTable.
Inside the Cancel event handler, the GridView EditIndex is set to -1 and the GridView is populated with data from the temporary DataTable saved in ViewState.
C#
protected void OnUpdate(object sender, EventArgs e)
{
    GridViewRow row = (sender as LinkButton).NamingContainer as GridViewRow;
    string name = (row.Cells[0].Controls[0]as TextBox).Text;
    string country = (row.Cells[1].Controls[0]as TextBox).Text;
    DataTable dt = ViewState["dt"]as DataTable;
    dt.Rows[row.RowIndex]["Name"] = name;
    dt.Rows[row.RowIndex]["Country"] = country;
    ViewState["dt"] = dt;
    gvCustomers.EditIndex = -1;
    this.BindGrid();
}
 
protected void OnCancel(object sender, EventArgs e)
{
    gvCustomers.EditIndex = -1;
    this.BindGrid();
}
 
VB.Net
Protected Sub OnUpdate(sender As Object, e As EventArgs)
    Dim row As GridViewRow = TryCast(TryCast(sender,LinkButton).NamingContainer, GridViewRow)
    Dim name As String = TryCast(row.Cells(0).Controls(0), TextBox).Text
    Dim country As String = TryCast(row.Cells(1).Controls(0), TextBox).Text
    Dim dt As DataTable = TryCast(ViewState("dt"), DataTable)
    dt.Rows(row.RowIndex)("Name") = name
    dt.Rows(row.RowIndex)("Country") = country
    ViewState("dt") = dt
    gvCustomers.EditIndex = -1
    Me.BindGrid()
End Sub
 
Protected Sub OnCancel(sender As Object, e As EventArgs)
    gvCustomers.EditIndex = -1
    Me.BindGrid()
End Sub
 
 

Demo

View Demo
 
 

Downloads

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