publicvoidAutoResizeRow(int rowIndex)

c une fonction de ton datagrid ...

sinon, rowdividerdoubleclick

protected virtual void OnRowDividerDoubleClick(DataGridViewRowDividerDoubleClickEventArgs e)
{
    DataGridViewRowDividerDoubleClickEventHandler handler = base.Events[EVENT_DATAGRIDVIEWROWDIVIDERDOUBLECLICK] as DataGridViewRowDividerDoubleClickEventHandler;
    if (((handler != null) && !this.dataGridViewOper[0x100000]) && !base.IsDisposed)
    {
        handler(this, e);
    }
    if ((!e.Handled && (e.Button == MouseButtons.Left)) && (e.RowIndex < this.Rows.Count))
    {
        if (e.RowIndex == -1)
        {
            this.AutoResizeColumnHeadersHeight(true, true);
        }
        else if (this.autoSizeRowsMode == DataGridViewAutoSizeRowsMode.None)
        {
            this.AutoResizeRowInternal(e.RowIndex, DataGridViewAutoSizeRowMode.AllCells, true, true);
        }
        else
        {
            this.AutoResizeRowInternal(e.RowIndex, MapAutoSizeRowsModeToRowMode(this.autoSizeRowsMode), true, true);
        }
    }
}

Eric