How Can I Merge Detail View With That Of Grid View On Selected Change

Please How can I show what is selected on the grid view to the details view
I have a drop down link for search
first on on btn_Search
it query the  the database and populate the information on the grid view
// gridview.datasource = null;
gridview.databind();
datatable dt  = me.query("select * from law where id = '" + drpL.selectedvalue +"'");
if (dt.rows.count > 0 )
{
gridview.datasource  =  dt
detailsview.datasource = dt
gridview.databind();
detailsview.databind();
}

// that is my select statement, I enabled selection...onselectedindexchanged="GridView_SelectedIndexChanged"
/*
My question is How do i on the code view write a simple code that will enable me to select a row and it will appear on the details view?

protected void GridView_SelectedIndexChanged(object sender, EventArgs e)
    {
        
    }

Can Some one help me out on this..
thanks
*/