C# WinForm登录时如何将MS Access数据赋值给全局类变量

现有代码 #

你的登录窗体实现代码如下：

private void button1_Click(object sender, EventArgs e)
{
    using (OleDbConnection connection = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\RAV21001310\\OneDrive\\Database1.accdb;"))
    {
        connection.Open();
        using (OleDbCommand command = new OleDbCommand("SELECT * FROM tblUser WHERE Username=@Username AND Password=@Password", connection))
        {
            command.Parameters.AddWithValue("@Username", username.Text);
            command.Parameters.AddWithValue("@Password", password.Text);
            using (OleDbDataReader reader = command.ExecuteReader())
            {
                int count = 0;
                while (reader.Read())
                {
                    count = count + 1;
                }
                if (count == 1)
                {
                    MessageBox.Show("Username and password is correct");
                }
                if (count > 1)
                {
                    MessageBox.Show("Duplicate username and password");
                }
                if (count == 0)
                {
                    MessageBox.Show("Username or password incorrect");
                }
            }
        }
        connection.Close();
    }
}

public class User
{
    public string Username;
    public string Password;
    public string FirstName;
    public string LastName;
    public string Gender;
    public int Age;
    public int TotalPoints;
}

解决方案步骤 #

1. 优化登录逻辑，读取并实例化User对象 #

修改登录按钮的点击事件，在验证成功时直接从OleDbDataReader中读取用户数据，赋值给User实例：

private void button1_Click(object sender, EventArgs e)
{
    User loggedInUser = null;
    using (OleDbConnection connection = new OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\RAV21001310\\OneDrive\\Database1.accdb;"))
    {
        connection.Open();
        using (OleDbCommand command = new OleDbCommand("SELECT * FROM tblUser WHERE Username=@Username AND Password=@Password", connection))
        {
            command.Parameters.AddWithValue("@Username", username.Text);
            command.Parameters.AddWithValue("@Password", password.Text);
            using (OleDbDataReader reader = command.ExecuteReader())
            {
                if (reader.Read())
                {
                    // 读取数据库字段，实例化User对象
                    loggedInUser = new User
                    {
                        Username = reader["Username"].ToString(),
                        Password = reader["Password"].ToString(),
                        FirstName = reader["FirstName"].ToString(),
                        LastName = reader["LastName"].ToString(),
                        Gender = reader["Gender"].ToString(),
                        Age = Convert.ToInt32(reader["Age"]),
                        TotalPoints = Convert.ToInt32(reader["TotalPoints"])
                    };
                    MessageBox.Show("登录成功");
                    // 打开主窗体并传递用户信息，或者存入全局变量
                    MainForm mainForm = new MainForm();
                    mainForm.LoggedInUser = loggedInUser;
                    this.Hide();
                    mainForm.Show();
                }
                else if (reader.HasRows)
                {
                    MessageBox.Show("存在重复的用户名和密码，请联系管理员");
                }
                else
                {
                    MessageBox.Show("用户名或密码错误");
                }
            }
        }
        // using块会自动关闭连接，无需手动调用connection.Close()
    }
}

2. 实现跨窗体访问用户信息的两种方式 #

方式一：窗体间直接传递

在目标窗体（比如MainForm）中添加User类型的属性：

public class MainForm : Form
{
    public User LoggedInUser { get; set; }

    private void MainForm_Load(object sender, EventArgs e)
    {
        // 使用LoggedInUser的信息
        labelWelcome.Text = $"欢迎 {LoggedInUser.FirstName} {LoggedInUser.LastName}";
        labelPoints.Text = $"当前积分：{LoggedInUser.TotalPoints}";
    }
}

方式二：全局静态类存储

创建一个静态类来保存当前登录用户，方便所有窗体直接访问：

public static class CurrentUser
{
    public static User LoggedInUser { get; set; }
}

在登录成功时赋值：

// 替换窗体传递的代码
CurrentUser.LoggedInUser = loggedInUser;

在其他窗体中直接调用：

private void OtherForm_Load(object sender, EventArgs e)
{
    if (CurrentUser.LoggedInUser != null)
    {
        labelUser.Text = CurrentUser.LoggedInUser.Username;
        labelPoints.Text = CurrentUser.LoggedInUser.TotalPoints.ToString();
    }
}

3. 额外优化建议 #

• 把User类的字段改为属性，符合C#编码规范：

public class User
{
    public string Username { get; set; }
    public string Password { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Gender { get; set; }
    public int Age { get; set; }
    public int TotalPoints { get; set; }
}

• 避免直接存储明文密码，数据库中应该存储密码哈希值，登录时比对哈希值而非明文。
• 使用command.Parameters.Add而非AddWithValue，可以明确指定数据类型，避免潜在的类型转换问题：

command.Parameters.Add("@Username", OleDbType.VarChar).Value = username.Text;
command.Parameters.Add("@Password", OleDbType.VarChar).Value = password.Text;

内容的提问来源于stack exchange，提问作者Ahmed Castro