Highlighting Rows in an ASP.Net DataGrid...
By: John Kilgo Date: January 11, 2003 Download the code.

I like the idea of highlighting rows in a GridView as the user scrolls the mouse up and down. The effect can be achieved using the RowDataBound event handler to add OnMouseOver and OnMouseOut attributes to handle the color change.

The aspx page code below for the GridView and its attributes is shown below. Notice that the OnRowDataBound event is defined. RowDataBound is a GridView method that fires as each row of data is added to the GridView. It allows us make changes, additions, etc to the contents of each row of data as they are created. 

<asp:GridView
    ID="GridView1"
    runat="server"
    BackColor="White"
    BorderColor="#999999"
    BorderStyle="Solid"
    BorderWidth="1px"
    CellPadding="3"
    DataSourceID="SqlDataSource1"
    ForeColor="Black"
    GridLines="Vertical"
    AutoGenerateColumns="False" onrowdatabound="GridView1_RowDataBound">
    <Columns>
        <asp:BoundField DataField="CompanyName" HeaderText="CompanyName" SortExpression="CompanyName" />
        <asp:BoundField DataField="LastName" HeaderText="LastName" SortExpression="LastName" />
        <asp:BoundField DataField="FirstName" HeaderText="FirstName" SortExpression="FirstName" />
        <asp:BoundField DataField="Phone" HeaderText="Phone" SortExpression="Phone" />
    </Columns>
    <FooterStyle BackColor="#CCCCCC" />
    <PagerStyle BackColor="#999999" ForeColor="Black" HorizontalAlign="Center" />
    <SelectedRowStyle BackColor="#000099" Font-Bold="True" ForeColor="White" />
    <HeaderStyle BackColor="Black" Font-Bold="True" ForeColor="White" />
    <AlternatingRowStyle BackColor="#CCCCCC" />
</asp:GridView>

<asp:SqlDataSource
    ID="SqlDataSource1"
    runat="server"
    ConnectionString="<%$ ConnectionStrings:AdventureWorksLTConnectionString %>"
    SelectCommand="SELECT TOP 20 CompanyName, LastName, FirstName, Phone FROM AdventureWorksLT.SalesLT.Customer ORDER BY LastName, FirstName">
</asp:SqlDataSource>
In RowDataBound event in the codebehind we add javascript attributes to each row which control the background color of the row as the mouse passes over the row. Notice that we capture the existing color of each row before we change it for the mouseover and then restore that color upon mouseout. If we don't do this then all rows will be permanently set to the mouseover color. 
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load ( object sender, EventArgs e )
    {

    }

    protected void GridView1_RowDataBound ( object sender, GridViewRowEventArgs e )
    {
        if ( e.Row.RowType == DataControlRowType.DataRow )
        {
            if ( e.Row.RowType == DataControlRowType.DataRow )
            {
                e.Row.Attributes.Add ( "onmouseover", "this.savedColor=this.style.backgroundColor;this.style.backgroundColor='Yellow'" );
                e.Row.Attributes.Add ( "onmouseout",  "this.style.backgroundColor=this.savedColor;" );
            }
        }
    }
}