C# WinForm中Login类UserEmail变量无法填充到Dashboard类变量如何解决

C# 类的字段初始化逻辑执行优先级高于构造函数，你在声明email字段时直接赋值为LogIn.UserEmail，该赋值动作执行时登录流程尚未完成、LogIn.UserEmail还未被赋值，后续LogIn.UserEmail更新后也不会同步到已经完成初始化的email字段中。你代码中构造函数内打印LogIn.UserEmail可以得到正确值，也能佐证该问题：构造函数执行时登录态已经就绪，但字段初始化阶段还没有拿到正确的登录邮箱。

1. 调整email字段的赋值时机，将赋值操作挪到构造函数内执行：

// 原字段声明处去掉赋值，仅保留声明
public string firstName, lastName, fullName, monthlyPayment, amountPayable, interest;
public string email;

public Dashboard()
{
    InitializeComponent();
    // 构造函数执行时登录态已就绪，此时赋值可以拿到正确的邮箱
    email = LogIn.UserEmail;
    Console.WriteLine(email);
    // 剩余原有构造函数逻辑保持不变
    Region = System.Drawing.Region.FromHrgn(CreateRoundRectRgn(0, 0, Width, Height, 25, 25));
    pnlNav.Height = btnDashboard.Height;
    pnlNav.Top = btnDashboard.Top;
    pnlNav.Left = btnDashboard.Left;
    btnDashboard.BackColor = Color.FromArgb(46, 51, 73);
}

2. 修复SQL注入风险：不要直接拼接SQL字符串，改为使用参数化查询，避免恶意输入导致数据库泄露或业务异常。示例如下（可根据你的DBAccess实现调整参数传递逻辑）：

private void Dashboard_Load(object sender, EventArgs e)
{
    string query = "Select MonthlyPayment, TotalPayable, Interest, ApplicantFirstName, Email from LoanApplication where Email = @Email";
    // 传入参数替换占位符，示例为SqlCommand的参数写法，适配你的DBAccess即可
    SqlParameter param = new SqlParameter("@Email", email);
    objDbAccess.readDatathroughAdapter(query, dtUsers, param);
    objDbAccess.closeConn();
    // 剩余原有数据绑定逻辑保持不变
    monthlyPayment = dtUsers.Rows[0]["MonthlyPayment"].ToString();
    amountPayable = dtUsers.Rows[0]["TotalPayable"].ToString();
    interest = dtUsers.Rows[0]["Interest"].ToString();
    fullName = dtUsers.Rows[0]["ApplicantFirstName"].ToString();
    email = dtUsers.Rows[0]["Email"].ToString();

    lblMonthlyPayment.Text = monthlyPayment;
    lblAmountPayable.Text = amountPayable;
    lblInterest.Text = interest;
    lblName.Text = fullName;
    lblEmail.Text = email;
}

你可以分别在email字段声明处、构造函数内email赋值处加断点，查看两个节点LogIn.UserEmail的取值，即可确认初始化时机带来的赋值差异。

内容的提问来源于stack exchange，提问作者Paul Smith