c# - How to get index of a column by name in a DataTable

Get column index by name from a DataTable
The DataTable class represents one table of in-memory data. The DataTable objects are conditionally case-sensitive. To create a DataTable programmatically the asp.net developers must first define its schema by adding DataColumn objects to the DataColumnCollection. To add rows to a DataTable, the developers must first use the NewRow() method to return a new DataRow object. The DataTable also contains a collection of Constraint objects that can be used to ensure the integrity of the data.

The following asp.net c# tutorial code demonstrates how we can get the index of a column by the column name from a DataTable. So we have to find the index of a specified DataColumn object by its name within a DataTable instance.

Here we used the DataTable class Columns property to get its columns collection as a DataColumnCollection object. Then we used DataColumnCollection’s IndexOf() method to get the specified column’s index using the column name within the columns collections.

The DataTable class Columns property gets the collection of columns that belong to this table. The Columns property value is a DataColumnCollection that contains the collection of DataColumn objects for the table. An empty collection is returned if no DataColumn objects exist.

The DataColumnCollection class represents a collection of DataColumn objects for a DataTable. The DataColumnCollection IndexOf() method searches for the specified DataColumn and returns the zero-based index of the first occurrence within the collection.

Here we used the IndexOf(String) method overload to get the specified column index by its name within a DataTable instance. The IndexOf(string? columnName) method overload has a parameter named columnName. This parameter is a String which is the name of the column to find.

The DataColumnCollection IndexOf(string? columnName) method returns an Int32 which is the zero-based index of the column with the specified name or -1 if the column does not exist in the collection.

So finally, using the DataTable Columns property the asp.net developers can get the DataColumnCollection object. And the DataColumnCollection class IndexOf() method allows the developers to get the index of a column’s object by its name within the specified DataTable.
IndexOfMethodDataTable.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data" %>

<!DOCTYPE html>
<script runat="server">
    void Button1_Click(object sender, System.EventArgs e)
    {
        DataTable dt = new DataTable();
        dt.TableName = "Books";

        DataColumn dc = new DataColumn();
        dc.ColumnName = "BookID";
        dc.DataType = typeof(int);

        DataColumn dc2 = new DataColumn();
        dc2.ColumnName = "BookName";
        dc2.DataType = typeof(string);

        DataColumn dc3 = new DataColumn();
        dc3.ColumnName = "Author";
        dc3.DataType = typeof(string);

        dt.Columns.AddRange(new DataColumn[] {dc,dc2,dc3});

        dt.Rows.Add(new object[] { "1", "Native Video in HTML5", "David Griffiths" });
        dt.Rows.Add(new object[] { "2", "Best iPhone Apps, Second Edition", "J.D. Biersdorfer" });
        dt.Rows.Add(new object[] { "3", "Microsoft® Silverlight® 4 Step by Step", "Laurence Moroney" });
        dt.Rows.Add(new object[] { "4", "Premiere Elements 8: The Missing Manual", "Chris Grover" });
        
        GridView1.DataSource = dt;
        GridView1.DataBind();

        //this line get the 'Author' DataColumn index in DataTable
        int columnIndex = dt.Columns.IndexOf("Author");
        Label1.Text = "'Author' DataColumn index in DataTable? = " + columnIndex;
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to get the index of the DataColumn with the specific name from DataTable in ado.net</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:DarkBlue; font-style:italic;">
            Using IndexOf() method - How to get the index of the
            <br /> DataColumn with the specific name from DataTable in ado.net
        </h2>
        <hr width="550" align="left" color="CornFlowerBlue" />
        <asp:GridView 
            ID="GridView1"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="525"
            HeaderStyle-BackColor="DarkOrchid"
            RowStyle-BackColor="SlateBlue"
            AlternatingRowStyle-BackColor="MediumSlateBlue"
            >
        </asp:GridView>
        <br /><br />
        <asp:Label
             ID="Label1"
             runat="server"
             Font-Size="Large"
             ForeColor="IndianRed"
             >
        </asp:Label>
        <br /><br />
        <asp:Button 
            ID="Button1"
            runat="server"
            OnClick="Button1_Click"
            Text="Populate GridView"
            Height="45"
            Font-Bold="true"
            ForeColor="DarkBlue"
            />
    </div>
    </form>
</body>
</html>
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