C#动态添加控件到窗体不显示

                 1
                private
                void UniqueForm_Load(object sender, EventArgs e)
 2        {
 3if (pFlag == 1)
 4            {
 5                 Label lbllevel = new Label();
 6                 lbllevel.Text = "请设置级数：";
 7                 lbllevel.Location = new System.Drawing.Point(38, 95);
 8                 lbllevel.AutoSize = true;
 9                 lbllevel.Visible = true;
10                 txtLevel = new TextBox();
11                 txtLevel.Name = "txtLevel";
12                 txtLevel.Location = new System.Drawing.Point(121, 92);
13                 txtLevel.Height = 21;
14                 txtLevel.Width = 150;
15                 txtLevel.Visible = true;
16this.groupBox1.Controls.Add(lbllevel);
17this.groupBox1.Controls.Add(txtLevel);
18            }
19 }