System.ArgumentException报错：数据源不能为空，求SQLite连接问题解决方案

Hey there! I see you're building a productivity tool and ran into a SQLite connection hiccup—let's get this sorted for you right away.

Root Cause of the Error #

The core issue here is how you've structured your connection string. You placed the @ symbol inside the double quotes, which turns it into part of the string literal instead of letting it act as a verbatim string prefix. SQLite ends up parsing a connection string that starts with @Data Source instead of the valid Data Source, so it can't recognize the actual database file path—hence the "Data Source cannot be empty" error.

Quick Fix for the Connection String #

Move the @ outside the quotes so it properly marks the string as verbatim (this also avoids escape character issues if you later use full file paths):

string dbcon = @"Data Source=KMS.db;Version=3;";

Note: I also removed the extra space after =—while SQLite might tolerate it, keeping the syntax consistent makes your code cleaner and less prone to unexpected issues.

Critical Security & Code Upgrade: Avoid SQL Injection #

Your current login query directly concatenates user input into the SQL string, which is a massive security risk (it leaves your app wide open to SQL injection attacks). Always use parameterized queries instead. Here's how to update your logic safely:

try {
    // Using 'using' ensures the connection is auto-disposed, preventing resource leaks
    using (SQLiteConnection sqlcon = new SQLiteConnection(dbcon)) 
    {
        sqlcon.Open();
        // Parameterized query to block SQL injection
        string query = "SELECT * FROM user WHERE Username = @Username AND Password = @Password";
        using (SQLiteCommand com = new SQLiteCommand(query, sqlcon))
        {
            // Bind user input to parameters (never concatenate directly!)
            com.Parameters.AddWithValue("@Username", textusername.Text);
            com.Parameters.AddWithValue("@Password", textpassword.Text);
            
            using (SQLiteDataReader dr = com.ExecuteReader())
            {
                int matchCount = 0;
                while (dr.Read()) {
                    matchCount++;
                }
                if(matchCount == 1) {
                    KMS_MainMenu MainMenu = new KMS_MainMenu();
                    MainMenu.Show();
                    this.Hide();
                } else {
                    EmptyErrorLabel.Visible = true;
                    EmptyErrorLabel.Text = "Invalid Username and / or Password";
                    textpassword.Clear();
                }
            }
        }
    }
} catch (Exception ex) {
    MessageBox.Show("Error while logging: " + ex);
}

Key Improvements Here: #

• using statements for all database objects: This guarantees resources are properly released even if an error occurs, no manual cleanup needed.
• Parameterized queries: Eliminates SQL injection risks entirely by separating user input from the SQL logic.
• Simplified the success/failure check: Since matchCount can only be 0 or 1 here, an else clause works perfectly instead of a separate if(i < 1) check.

Quick Additional Check #

Double-check that KMS.db is in the right location: If you're running the app from Visual Studio, the database file should live in your project's output folder (usually bin/Debug or bin/Release). If it's missing, set the file's "Copy to Output Directory" property to "Copy if newer" in Visual Studio's Solution Explorer.

内容的提问来源于stack exchange，提问作者Francisco Mendonça