关闭 C# Windows 窗体应用程序时重置模态窗体

Question

I am writing a C# Windows Forms App Online Store GUI that interfaces with a database. One of the things I have to do is handle customers that are already in the database. From the main menu form they click the 'Returning Customer' button, and enter their email and password. The data entered is then checked against the customers stored in the database, and if it's verified, their user information is filled into text boxes (Name, Credit Card info, CVS, etc...) and the order form becomes visible. I have no issues there. The issue I'm having is that if a returning customer successfully logs in, then cancels out back to the main menu, the next person to click the 'Returning Customer' button pulls up the form with the first user's information already filled in and visible, since both the this.Close() and the this.DialogResult = DialogResult.Cancel methods both only hide the form rather than actually close and free it. But then if I use this.Dispose() on the Returning Customer Form to free it, it can't be reopened.
My question is: is there an easy way to handle this? I'm self taught in C# so forgive my inexperience. Thank you for any help you can give.

Per request see Form1 (Main Menu Form) code below:

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Database_Interface_Project
{
    public partial class Form1 : Form
    {
        // Removed SqlConnectionString for security purposes.
        public SqlConnection cnn = new SqlConnection(connectionString);


        // Main Menu Form
        public Form1()
        {
            InitializeComponent();
        }

        // New Customer Form
        Form2 newCustomer = new Form2();

        private void newCusButt_Click(object sender, EventArgs e)
        {
            newCustomer.ShowDialog();
        }

        // Returning Customer Form
        ReturningCustomer returningCustomer = new ReturningCustomer();
        private void RetCusButt_Click(object sender, EventArgs e)
        {
            returningCustomer.ShowDialog();

        }

        private void exitButt_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        // Manager Menu Form
        Manager managerMenu = new Manager();
        private void managerButt_Click(object sender, EventArgs e)
        {
            managerMenu.ShowDialog();
        }
    }
}```

Answer 1

You just need to re-instantiate returningCustomer form in order to reset its fields.

private void RetCusButt_Click(object sender, EventArgs e)
{
    using (var returningCustomer = new ReturningCustomer())
    {
        returningCustomer.ShowDialog();
    }
}

Using statement calls Dispose() automatically after the using-block is left.

Note : In your case you need to dispose ShowDialog appropriately to avoid GDI leak, since it has side effect of keeping the GDI objects alive.