how to select data from excel spreadsheet and bind to datagrid

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C#

.NET

SQL-Server

C#4.0

MS-Excel

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I am working on a tool that basically allow users select an excel file from their computer, preview it in a datagrid before submitting to the database. Currently this is what the code that opens the file looks like

private void btn_browse_file_Click(object sender, EventArgs e)
     {
         OpenFileDialog openFileDialog1 = new OpenFileDialog();
         openFileDialog1.CheckFileExists = true;
         openFileDialog1.AddExtension = true;
         openFileDialog1.Multiselect = false;
         openFileDialog1.Filter = "Excel files (*.xls) | *.xlsx";
         openFileDialog1.Title = "Select a spreadsheet file";


         if (openFileDialog1.ShowDialog() == DialogResult.OK)
         {
             openFileDialog1.OpenFile();

          //  MessageBox.Show(openFileDialog1.FileName.ToString());
             label_display_file_name.Text = openFileDialog1.FileName.ToString();
         }

     }

and this is the code that is meant to display the excel file in the datagridview

private void btn_preview_Click(object sender, EventArgs e)
{
    OleDbConnection ConnectToExcel = new OleDbConnection();
    DataSet excelds = new DataSet();
    OleDbDataAdapter excelda = new OleDbDataAdapter();
    OleDbCommand excelcmd = new OleDbCommand();
    ConnectToExcel = new OleDbConnection (String.Format(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=""Excel 12.0;HDR=YES;IMEX=1;""", openFileDialog1.FileName.ToString()));
    excelcmd = new OleDbCommand (String.Format("SELECT * FROM [{0}$]", ConnectToExcel, openFileDialog1.FileName));
    excelda = new OleDbDataAdapter(excelcmd);
    excelda.Fill(excelds);
    dataGridView1.DataSource = excelds.Tables[0];


}

For some reasons I don't yet know, the code to display the excel file on the datagrid gives me the following error "Fill:SelectCommand.Connection property has not been initialized".

Any help or ideas on how to get this work will be much appreciated.