如何从放置在窗体上的面板中捕获值

我不了解如何在放置在窗体面板上的文本框中捕获值。我正在尝试使用这些值更新数据库表。

谁能指出我正确的方向？

代码：

private void btnSupplier_Click(object sender, EventArgs e)
    {
        try
        {
            Panel pnlAddSupplier = new Panel();
            TextBox txtSupplierID = new TextBox();
            TextBox txtSupplierName = new TextBox();
            Button btnAddSupplier = new Button();
            Label lblSupplierID = new Label();
            Label lblSupplierName = new Label();

            // Initialize the Panel control.
            pnlAddSupplier.Location = new Point(56, 74);
            pnlAddSupplier.Size = new Size(200, 200);
            // Set the Borderstyle for the Panel to three-dimensional.
            pnlAddSupplier.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;

            // Initialize the Label and TextBox controls.
            lblSupplierID.Location = new Point(60, 0);
            lblSupplierID.Text = "Supplier ID";
            lblSupplierID.Size = new Size(104, 20);
            txtSupplierID.Location = new Point(20, 40);
            txtSupplierID.Text = "";
            txtSupplierID.Size = new Size(152, 20);

            lblSupplierName.Location = new Point(20, 70);
            lblSupplierName.Text = "Supplier Name";
            lblSupplierName.Size = new Size(150, 20);
            txtSupplierName.Location = new Point(20, 90);
            txtSupplierName.Text = "";
            txtSupplierName.Size = new Size(152, 20);

            lblSupplierID.Location = new Point(16, 16);
            lblSupplierID.Text = "Supplier ID";


            btnAddSupplier.Location = new Point(60, 120);
            btnAddSupplier.Text = "Add";
            btnAddSupplier.Click += btnAddSupplier_Click;
            // Add the Panel control to the form. 
            this.Controls.Add(pnlAddSupplier);
            // Add the Label and TextBox controls to the Panel.
            pnlAddSupplier.Controls.Add(lblSupplierID);
            pnlAddSupplier.Controls.Add(txtSupplierID);
            pnlAddSupplier.Controls.Add(lblSupplierName);
            pnlAddSupplier.Controls.Add(txtSupplierName);
            pnlAddSupplier.Controls.Add(btnAddSupplier);

        }
        catch { }
    }

 public void btnAdd_Click(object sender, EventArgs e)
        {
            string username= //how to assign textbox value?;
            int age = //how to assign textbox value;

            MySql.Data.MySqlClient.MySqlCommand cmd = new MySql.Data.MySqlClient.MySqlCommand();

            string query = "INSERT INTO table(username, age) VALUES ('@xxx', '@xxx') "; 

             //please not these values are for demonstration.

            using (connection)
            {
                  ObjDb.OpenConnection();
                ObjDb.ExecuteNonQuery(query, connection);
            }
        }

如您所见，此代码对SQL注入开放，并且我想使用参数。为此，我需要捕获详细信息输入。如何做到这一点？

我尝试分配，supplierID = txtSupplierID.Text但收到一条消息说不txtSupplier.Text存在。

谢谢你。