WPF健身应用数据库用户删除功能失效问题求助

我在学校作业中需要开发一款健身应用，主页面通过以下代码将文本框的用户名传入Settings类：

WPF_login.Pages.Settings s = new WPF_login.Pages.Settings(txtUsername.Text);

但在Settings页面点击删除按钮时，无法删除对应用户。相关代码如下：

namespace WPF_login.Pages
{
    /// <summary>
    /// Interaction logic for Settings.xaml
    /// </summary>
    class Person
    {
        public string name;
        public string getName(string namel)
        {
            return name;    
        }
    }
    public partial class Settings : Page
    {
        public string name;
        private SqlConnection connection;
    
        public Settings(string loggedUser)
        {
            InitializeComponent();

            // Save the value of loggedUser in the name variable
            name = loggedUser;

            Person p = new Person();

            p.getName(loggedUser);

            string connectionString = "Data Source=DILEEKALAPTOP;Initial Catalog = FitnessGuidDB; Integrated Security = True;";
            connection = new SqlConnection(connectionString);

            bool loggedUserExists = CheckLoggedUserExists(loggedUser);

            if (!loggedUserExists)
            {
                MessageBox.Show($"Success: {p.name} exists", "Infromation", MessageBoxButton.OK, MessageBoxImage.Information);
            }
        }
        private bool CheckLoggedUserExists(string luser)
        {
            bool userExists = false;

            try
            {
                // Open the connection to the database
                connection.Open();

                // Create a new SqlCommand object to execute the SELECT statement
                SqlCommand command = new SqlCommand($"SELECT * FROM UserRegister WHERE U_name = '{name}'", connection);

                // Execute the query and get the results
                SqlDataReader reader = command.ExecuteReader();

                // Check if there are any rows in the result set
                if (reader.HasRows)
                {
                    userExists = true;
                }

                // Close the reader
                reader.Close();
            }
            catch (Exception ex)
            {
                // Handle any errors that occur
                MessageBox.Show($"Error: {ex.Message}", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
            }
            finally
            {
                // Close the connection to the database
                connection.Close();
            }

            return userExists;
        }



        public Settings()
        {
            
        }

        
        private void mobilechangebtn_Click(object sender, RoutedEventArgs e)
        {
        
        }


        private void lbl_welcome_Loaded(object sender, RoutedEventArgs e)
        {

        }

        private void lbl_welcome_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
        {
           

        }

        private void Border_Loaded(object sender, RoutedEventArgs e)
        {
            lbl_welcome.Content = name;
        }

        private void mobilechangebtn_Click_1(object sender, RoutedEventArgs e)
        {
          
        }

        private void deleteuserbtn_Click(object sender, RoutedEventArgs e)
        {
            Settings settings = new Settings();
           string loggedUser = settings.name;
           // MessageBox.Show($"Success: {loggedUser} exists", "Infromation", MessageBoxButton.OK, MessageBoxImage.Information);
            string LoggedUser = "dummy";
            string connectionString = "Data Source=DILEEKALAPTOP;Initial Catalog = FitnessGuidDB; Integrated Security = True;";
            connection = new SqlConnection(connectionString);
            try
            {
                // Open the connection to the database
                connection.Open();

                // Create a new SqlCommand object to execute the DELETE statement
                SqlCommand command = new SqlCommand($"DELETE FROM UserRegister WHERE U_name = '{LoggedUser}'", connection);

                // Execute the query
                command.ExecuteNonQuery();

                // Set LoggedUser to null or an empty string to delete it
                LoggedUser = null; // or LoggedUser = "";

                // Show a success message to the user
                MessageBox.Show($"Successfully deleted user: {LoggedUser}", "Success", MessageBoxButton.OK, MessageBoxImage.Information);
                WPF_login.CreateUser c = new WPF_login.CreateUser();
                c.Show();
                //this.Hide();
            }
            catch (Exception ex)
            {
                // Handle any errors that occur
                MessageBox.Show($"Error: {ex.Message}", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
            }
            finally
            {
                // Close the connection to the database
                connection.Close();
            }

        }
    }
}

我尝试过创建名为Person的自定义类并将其name设为登录用户名，也尝试过使用属性，但都无法解决问题。请问我哪里出错了？

1. 删除按钮事件的核心错误 #

在deleteuserbtn_Click方法里，你犯了两个致命错误：

• 新建了一个空的Settings实例，这个实例的name字段根本没有赋值，获取不到当前登录用户
• 硬编码了LoggedUser = "dummy"，直接导致删除的是名为dummy的用户，而非当前登录用户

修复后的删除按钮代码：

private void deleteuserbtn_Click(object sender, RoutedEventArgs e)
{
    // 直接使用当前页面已保存的name字段，无需新建实例
    string loggedUser = name;
    if (string.IsNullOrEmpty(loggedUser))
    {
        MessageBox.Show("无法获取当前登录用户信息", "错误", MessageBoxButton.OK, MessageBoxImage.Error);
        return;
    }

    string connectionString = "Data Source=DILEEKALAPTOP;Initial Catalog = FitnessGuidDB; Integrated Security = True;";
    // 使用using块自动管理连接生命周期，无需手动关闭
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        try
        {
            connection.Open();
            // 使用参数化查询避免SQL注入，同时确保用户名正确传入
            SqlCommand command = new SqlCommand("DELETE FROM UserRegister WHERE U_name = @UserName", connection);
            command.Parameters.AddWithValue("@UserName", loggedUser);

            int rowsAffected = command.ExecuteNonQuery();
            if (rowsAffected > 0)
            {
                MessageBox.Show($"成功删除用户: {loggedUser}", "成功", MessageBoxButton.OK, MessageBoxImage.Information);
                WPF_login.CreateUser c = new WPF_login.CreateUser();
                c.Show();
                NavigationService?.GoBack(); // 返回上一页
            }
            else
            {
                MessageBox.Show("未找到该用户，删除失败", "提示", MessageBoxButton.OK, MessageBoxImage.Information);
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show($"错误: {ex.Message}", "错误", MessageBoxButton.OK, MessageBoxImage.Error);
        }
    }
}

2. Person类完全无效 #

你创建的Person类逻辑混乱：getName方法接收参数但从未给p.name赋值，调用后p.name依然是null，这个类完全没起到作用，直接删除即可。

3. CheckLoggedUserExists方法的逻辑错误 #

• 方法传入了luser参数，但SQL语句里用的是类的name字段，参数完全没用到
• 判断逻辑颠倒：!loggedUserExists时提示用户存在，实际应该是loggedUserExists为true时才提示

修复后的检查方法：

private bool CheckLoggedUserExists(string luser)
{
    bool userExists = false;
    string connectionString = "Data Source=DILEEKALAPTOP;Initial Catalog = FitnessGuidDB; Integrated Security = True;";
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        try
        {
            connection.Open();
            // 使用参数化查询，用传入的luser参数
            SqlCommand command = new SqlCommand("SELECT 1 FROM UserRegister WHERE U_name = @UserName", connection);
            command.Parameters.AddWithValue("@UserName", luser);

            // 用ExecuteScalar判断是否存在，比DataReader更高效
            object result = command.ExecuteScalar();
            userExists = result != null;
        }
        catch (Exception ex)
        {
            MessageBox.Show($"错误: {ex.Message}", "错误", MessageBoxButton.OK, MessageBoxImage.Error);
        }
    }
    return userExists;
}

4. 修正Settings构造函数 #

移除无用的Person类，修正提示逻辑：

public Settings(string loggedUser)
{
    InitializeComponent();
    name = loggedUser;

    bool loggedUserExists = CheckLoggedUserExists(loggedUser);

    if (loggedUserExists)
    {
        MessageBox.Show($"成功: {name} 存在", "信息", MessageBoxButton.OK, MessageBoxImage.Information);
    }
    else
    {
        MessageBox.Show($"用户 {name} 不存在", "提示", MessageBoxButton.OK, MessageBoxImage.Warning);
    }
}

内容的提问来源于stack exchange，提问作者Dileeka Dasanayake