银行账户程序存款按钮不起作用

该程序是一个具有两个选项卡的GUI。在第一个选项卡上有四个文本框，分别显示姓名、身份证、年龄和帐户余额。这个选项卡上还有一个按钮，可以将帐户添加到第二个选项卡上的组合框中。在第二个标签上，有组合框和四个文本框，分别是姓名、id、年龄和余额。当我从组合框中选择一个名称时，四个文本框会自动填充它们的信息。我遇到的问题是，我必须有一个提款和存款按钮，用户可以在该按钮中输入金额，并将其减去或添加到文本框中的余额中。我有一些撤回按钮的示例代码，有人已经帮过我了。有人能告诉我为什么当我按下按钮时它没有改变平衡吗？

class BankAccount
{
    //attributes
    public string accountID;
    public string customerName;
    public int customerAge;
    public double balance;
    public const double DEFAULT_BALANCE = 500.00;
    //construct
    public BankAccount()
    {
    }
    public BankAccount(string anID, string aName, int anAge, double aBalance)
    {
        accountID = anID;
        customerName = aName;
        customerAge = anAge;
        balance = aBalance;
        if (aBalance == 0)
        {
            balance = DEFAULT_BALANCE;
        }
        else
        {
            balance = aBalance;
        }
    }
    public BankAccount(string anID, string aName, int anAge)
    {
        accountID = anID;
        customerName = aName;
        customerAge = anAge;
        balance = DEFAULT_BALANCE;
    }



    //accessors
    public void SetID(string anID)
    {
        accountID = anID;
    }
    public void SetName(string aName)
    {
        customerName = aName;
    }
    public void SetAge(int anAge)
    {
        customerAge = anAge;
    }
    public void SetBalance(double aBalance)
    {
        balance = aBalance;
    }
    public string GetID()
    {
        return accountID;
    }
    public string GetName()
    {
        return customerName;
    }
    public int GetAge()
    {
        return customerAge;
    }
    public double GetBalance()
    {
        return balance;
    }

}
}

这是表格

 public partial class Form1 : Form
 {
    private List<BankAccount> account = new List<BankAccount>();
    public Form1()
    {
        InitializeComponent();
    }

    private void btnAddAccount_Click(object sender, EventArgs e)
    {
        BankAccount aBankAccount = new BankAccount(txtAccountID.Text, txtName.Text,
            int.Parse(txtAge.Text), double.Parse(txtBalance.Text));
        account.Add(aBankAccount);
        AddToComboBox();
        ClearText();

    }
    private void AddToComboBox()
    {
        cboAccount.Items.Clear();
        foreach (BankAccount person in account)
        {
            cboAccount.Items.Add(person.GetName());

        }

    }
    private void ClearText()
    {
        txtName.Clear();
        txtAccountID.Clear();
        txtBalance.Clear();
        txtAge.Clear();
        txtAccountID.Focus();

    }
    private void cboAccount_SelectedIndexChanged(object sender, EventArgs e)
    {
        txtNameTab2.Text = account[cboAccount.SelectedIndex].customerName;
        txtAgeTab2.Text = account[cboAccount.SelectedIndex].customerAge.ToString();
        txtAccountIDTab2.Text = account[cboAccount.SelectedIndex].accountID.ToString();
        txtBalanceTab2.Text = account[cboAccount.SelectedIndex].balance.ToString();
    }

    private void btnWithdraw_Click(object sender, EventArgs e)
    {
        double amount = 0;
        if (double.TryParse(txtWithdraw.Text, out amount))
        {
            if (amount > 0)
            {
                BankAccount currentAccount = account[cboAccount.SelectedIndex];
                double currentBalance = currentAccount.GetBalance();
                double amountLeft = currentBalance - amount;
                if (amountLeft >= 0)
                {
                    currentAccount.SetBalance(amountLeft);
                    txtBalanceTab2.Text = amountLeft.ToString("c");
                }
                else
                {
                    MessageBox.Show("You don't have enough money!");
                }

            }
        }
    }

}
}