方法不会检查文件是否匹配字符串

此代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
namespace WindowsFormsApplication2
{
public partial class Form2 : Form
{
    private void Form2_Load(object sender, EventArgs e)
    {
        pictureBox2.SizeMode = PictureBoxSizeMode.Zoom;
    }
    public Form2()
    {
        InitializeComponent();
    }
    public bool radioButtons()
    {
        if (!userRadioButton.Checked && !adminRadioButton.Checked)
        {
            MessageBox.Show("You must select an account type");
            return false;
        }
        else
        {
            return true;
        }
    }
    public void button1_Click(object sender, EventArgs e)
    {
        bool a = radioButtons();
        if (a == true)
        {
            string userName = userNameBox.Text;
            string password = passwordBox.Text;
            if (checkUsernameValid() && checkUsernameNotExist() && checkPasswordsValid() && checkPasswordsMatch())
            {
                allOK();
            }

        }   
    } 
    public void mySW()
    {
         string path = @"C:'Other'myFile.txt";
        string userName = userNameBox.Text;
        string password = passwordBox.Text;
        using (StreamWriter writer = new StreamWriter(path, true))
        {
            writer.WriteLine(userName+" "+password);
            writer.WriteLine();
            writer.Close();
            writer.Dispose();
        }
        MessageBox.Show("Thanks for registering! 'n'nYou may now log in!","Registration SuccessFul");
        Application.OpenForms[0].Show();
        this.Close();
    }
    public bool checkUsernameValid()
    {
        if (userNameBox.Text == "")
        {
            MessageBox.Show("Username cannot be empty", "Invalid Username Entry");
            return false;
        }
        else
            return true;
    }
    public bool checkPasswordsMatch()
    {
        if (!passwordBox.Text.Equals(repeatPasswordBox.Text))
        {
            MessageBox.Show("Sorry, your passwords do not match, try again", "Password Error");
            passwordBox.Text = "";
            repeatPasswordBox.Text = "";
            return false;
        }
        else
            return true;
    }
    public bool checkUsernameNotExist()
    {
        var userNames = File.ReadAllLines(@"C:'Other'myFile.txt");
        if (userNames.Contains(userNameBox.Text))
        {
            MessageBox.Show(
                 "Sorry, that user name is not available, try again",
                 "Invalid Username Entry");
            userNameBox.Text = "";
            passwordBox.Text = "";
            repeatPasswordBox.Text = "";
            return false;
        }
        else
            return true;
    }
    public void allOK()
    {
        if (!userNameBox.Text.Contains("Username: " + userNameBox.Text) && passwordBox.Text == repeatPasswordBox.Text)
            {
                mySW();
            }
    }
    public bool checkPasswordsValid()
    {
        if (passwordBox.Text == "")
        {
            MessageBox.Show("Password fields cannot be empty", "Password Error");
            return false;
        }
        else
            return true;
    }
   }
}

是完整的代码，但我一直在查看它。我仍然无法弄清楚为什么它让我注册相同的用户名????我不明白它在调试器中如何说"是的，有一个匹配的字符串"，所以让我们返回 true？！

注意：我已经设法用ReadAllText而不是ReadAllLines对其进行排序，但我不明白为什么行不起作用？ 有人知道吗？

PS 这段代码，有没有更简单、更安全的方法呢？ 我想要的只是一个简单的登录屏幕哈哈