问create TextBoxs表中出现类型为'System.NullReferenceException‘的异常

EN

private string[][] GenerateTable(int colsCount, int rowsCount)
{
    string[][] controls_Array = new string[7][];            
    //Create the Table and Add it to the Page
    Table table = new Table();
    table.ID = "Table1";
    table.CellSpacing =5;
    table.BorderWidth = 0;

    Page.Form.Controls.Add(table);
    TableColoumnHeader(table,table.Rows);
    // Now iterate through the table and add your controls 
    for (int i = 0; i < rowsCount; i++)
    {
        TableRow row = new TableRow();
        Label lbl = new Label();
        lbl.Text = "row"+i.ToString();
        ///
        TableCell TC = new TableCell();
        TC.Controls.Add(lbl);
        row.Cells.Add(TC);
        for (int j = 0; j < colsCount; j++)
        {
            TableCell cell = new TableCell();

            // Add the control to the TableCell
            if(j==colsCount-1)
            {
                CheckBox chkb = new CheckBox();
                chkb.ID = "CheckBoxRow_" + i + "Cols_" + j;
                cell.Controls.Add(chkb);
                controls_Array[j][i] = chkb.ID;
            }
            else
            {    
                TextBox tb = new TextBox();
                // Set a unique ID for each TextBox added
                tb.ID = "TextBoxRow_" + i + "Col_" + j;
                cell.Controls.Add(tb);
                controls_Array[j][i] = tb.ID;// this line where is the mentioned error occurred.
            }

            // Add the TableCell to the TableRow
            row.Cells.Add(cell);
        }
        // Add the TableRow to the Table
        table.Rows.Add(row);

    }/**/
    return controls_Array;

}