生成TextBoxes矩阵

Question

我试图在Form中动态生成TextBoxes矩阵。在行中     textbox [i] [j] .Size = new Size（w，h）; 我收到错误＆＃34; NullReferenceException＆＃34;。

TextBox[][] textbox = new TextBox[100][];
        int x_point = 70;
        int y_point = 70;
        int h = 30;
        int w = 40;
        for (int i = 0; i < number_columns; i++)
        {
            for (int j = 0; j < number_columns; j++)
            {
                textbox[i][j] = new TextBox();
                textbox[i][j].Size = new Size(h, w); // Here I get the error
                textbox[i][j].Location = new Point(x_point, y_point);
                y_point = y_point + 40;
                this.Controls.Add(textbox[i][j]);
            }
            y_point = 70;
            x_point =x_point + 30;
        }