c# - 列表框UI因SelectedIndexChanged事件而卡住

发生的事情是，如果我在listBox1_SelectedIndexChanged方法中包含代码，则每次按下添加现金，保存或刷新按钮时UI都会卡住。

如果我删除listBox1_SelectedIndexChanged中的代码，它会很好地工作。

        private void LoadAccounts()
        {
            accounts.Clear();
            accounts = DBAccess.LoadAccounts();
            UpdateListBox();
        }

        private void UpdateListBox()
        {
            listBox1.DataSource = null;
            listBox1.DataSource = accounts;
            listBox1.DisplayMember = "Username";

        }

        private void btnAddCash_Click(object sender, EventArgs e)
        {
            string userName = listBox1.GetItemText(listBox1.SelectedItem);

            if ( Int32.TryParse(txtAddCash.Text, out int cash) )
            {
                DialogResult dr = MessageBox.Show($"Add {txtAddCash.Text} cash to {userName}?", "Add Cash", MessageBoxButtons.YesNo);
                if (dr == DialogResult.No)
                    return;

                AccountModel acc = new AccountModel();

                acc.Username = userName;
                acc.LeftCash = cash;

                DBAccess.AddCash(acc);

                txtAddCash.Text = "";

                LoadAccounts();
            }
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string selected = ((AccountModel)listBox1.SelectedItem).Username;
            int leftCash = accounts.Where(a => a.Username == selected).Select(a => a.LeftCash).First();

            lblLeftCash.Text = leftCash.ToString();
        }

我简述了发生了什么

就像更新的用户界面在旧列表框用户界面的后面