How to use StreamReader and read from certain parts of the text file?

Question

I'm trying to make a login system with the sign-up already completed. I want to make it where you press the login button then it uses StreamReader to read the file that has been updated with my sign-up form. The problem is that I have structured how the file is written (example: when a user enters their details it saves their details in a structure like Username: johndoe Password: Password1 using StreamWriter in my sign-up form). But when I use StreamReader it reads the whole line instead of some parts. How would I read only some parts of my text file?

Code for sign-up form:

        bool valid = true;
        List<string> errorMessages = new List<string>();

        if (string.IsNullOrWhiteSpace(txtUsername.Text))
        {
            valid = false;
            errorMessages.Add("Username cannot be left empty.");
        }
        if (string.IsNullOrWhiteSpace(txtPassword.Text))
        {
            valid = false;
            errorMessages.Add("Please enter a password.");
        }
        if (txtConfirmPass.Text != txtPassword.Text)
        {
            valid = false;
            errorMessages.Add("Passwords do not match. Please enter matching passwords.");
        }
        if (valid == false)
        {
            string message = string.Join(Environment.NewLine, errorMessages);
            MessageBox.Show(message, "Validate Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        else if(valid == true)
        {
            Random rnd = new Random();
            string userID = rnd.Next(0, 100000).ToString("D6");
            //Use StreamWriter class.
            using (StreamWriter sw = new StreamWriter("Test.txt", true))
            {
                sw.Write("\n" + "UserID: " + userID + "\n");
                sw.Write("Username: " + txtUsername.Text + "\n");
                sw.Write("Password: " + txtPassword.Text + "\n");
                sw.Write("------------------------------------");

                MessageBox.Show("Details have been saved");
                frmLogin login = new frmLogin();
                login.Show();
                this.Hide();
            }
        }           

Code for login form:

private void btnLogin_Click(object sender, EventArgs e)
    {
        bool valid = false;
        using (StreamReader sr = new StreamReader("Test.txt"))
        {
            if(txtboxUser.Text == sr.ReadToEnd() && txtboxPass.Text == sr.ReadToEnd())
            {
                valid = true;
                MessageBox.Show("Granted.");
            }
            else if(valid == false)
            {
                MessageBox.Show("Error");
            }
        }
    }

Answer 1

You have problems with your code, because you want to do too much in one method. You should separate your concerns

In your case: you shouldn't mix the communication with operator with the way that the input data is serialized.

If you separate the HMI from the way you save and read the input:

• Easier to reuse: if you need to read the saved logged in data, without having to ask it from the operator again: just read it.
• Easier to change: if you want a different HMI, you can still save in in the original format. If you want to save it in encrypted format, your HMI doesn't need to change.
• Easier to Test: you can unit test Save / Read the file, without needing the operator input.

So separate the HMI from saving / reading the file, separate from processing the login data. This will take some extra typing, but your code will be much easier to understand, much easier to test, and future changes will have less impact on existing code.

For this you'll need a class that contains the login data. Something like this:

class User
{
    public int Id {get; set;}
    public string Name {get; set;}
    public string Password {get; set;}
}

HMI for users

To display a User in the HMI, or to fetch it from the HMI. In your form class:

public User ReadUser()
{
    return new User
    {
        Id = this.CreateUserId(),
        Name = this.txtUserName.Text,
        Password = this.txtPassword.Text,
    };
}

// not sure if you need this:
public void DisplayUser(User user)
{
    this.txtUserName.Text = user.Name,
    this.txtPassword.Text = user.Password,
}

Consider to create a property:

public User User
{
    get => new User {Id = this.CreateUserId(), ...},
    set
    {
        this.txtUserName.Text = value.Name,
        ...
    }
}

If in future you want to display users differently, like in a DataGridView, or a ComboBox, there will be only once place where you'll have to implement the changes.

Serializing users

My advice would be to stick to common formats, like CSV, XML, JSon. This would make life so much easier for you, because you can use NUGET packages for this.

If you can't convince your project leader that this would be a better solution and he still wants you to user you home invented format, you need two methods:

public void Serialize(User user, string fileName)
{
     using (var textWriter = System.IO.File.CreateText(fileName, ...))
     {
          ... // see your own code
     }
}

By the way: why do you write `\n, why don't you use TextWriter.WriteLine

Deserialize a User

Currently your file has the following layout:

• empty line

• A line with "UserId: " + Id

• A line with "UserName: " + Name

• A line with "Password: " + Password

  public User Deserialize(string fileName) { using (var textReader = System.IO.File.OpenText(fileName, ...)) { string emptyLine = textReader.ReadLine(); if (emptyLine == null) ... // TODO: decide what to do if invalid file format. Exception?

       string txtId = textReader.ReadLine();
       if (txtId == null)
           ... // TODO: decide what to do if invalid file format
  
       int id = Int32.Parse(txtId);
       // TODO: handle invalid txtId format. Exception?
  
       string name = textReader.ReadLine();
       string password = textReader.ReadLine();
       // TODO: handle invalid name / password;
  
       return new User
       {
           Id = id,
           Name = name,
           Password = password,
       }
   }
  

  }

Do you see, that if in future you change the format in which Users are saved, that you only need to change the two serialization methods? for instance, if you think that passwords need to be encrypted in the file, or if you think that JSON format is better.

Because of the separation of concerns, you can use the serialization of Users also in case you don't need to display it.

The separation of concerns also makes unit test easier } }

sw.Write("\n" + "UserID: " + userID + "\n"); sw.Write("Username: " + txtUsername.Text + "\n"); sw.Write("Password: " + txtPassword.Text + "\n"); sw.Write("------------------------------------");

Answer 2

Do you want to check if the user has entered the correct username and password by traversing the txt file？

Test info structure:

UserID: 016696
Username: kkk
Password: p123

Here is a simple you can refer to.

private void btnLogin_Click(object sender, EventArgs e)
{
    string username = "";
    string password = "";
    bool ischecked = false; // check if the Username line is read
    bool loginsuccess = false; // check if succeed

    string line;

    // Read the file and display it line by line.  
    System.IO.StreamReader file = new System.IO.StreamReader("Test.txt");
    while ((line = file.ReadLine()) != null)
    {
        // if true, this is password line
        if (ischecked)
        {
            // get password
            // call Trim to remove extra spaces
            password = line.Split(':')[1].Trim();

            // check username and password
            if (txtUsername.Text == username && txtPassword.Text == password)
            {
                MessageBox.Show("Login Successfully");
                loginsuccess = true; //  login in success
                break;
            }
            // reset boolean
            ischecked = false;
        }

        // read Username line, next line is the corresponding password
        if (line.Split(':')[0] == "Username")
        {
            username = line.Split(':')[1].Trim();
            // set boolean to true
            ischecked = true;
        }
    }

    file.Close();
    
    // login failed
    if(!loginsuccess)
    {
        MessageBox.Show("Wrong username or password");
    }
}

Answer 3

You can try to use ReadLine() method in StreamReader like the one shown below, you should keep track that 2nd line contains the user name and the 3rd line contains the password. Also, you should use a Regex to split and get the values from the text or you could use a : delimiter and trim the values before comparison.

using (StreamReader sr = new StreamReader(path))
{
    int counter = 0;
    while (sr.Peek() >= 0)
    {
        string content = sr.ReadLine();
        var userName = content.split(':')[1].trim()...
        counter++;
    }
}

Note: The StreamReader directly reads from the file, so you have to perform string manipulation operations. Instead, you might also consider other approaches like a cache or a database operation to persist the values across pages / windows.