C#窗体实现登陆注册

在展示内容前，先说明一下遇到的几个小问题：

1.在与 SQL Server 建立连接时出现与网络相关的或特定于实例的错误。未找到或无法访问服务器。请验证实例名称是否正确并且 SQL Server 已配置为允许远程连接。 (provider: SQL 网络接口, error: 26 - 定位指定的服务器/实例时出错)。

解决方法：

启动这三个服务。

2.System.Data.SqlClient.SqlException: 用户xxxx 登录失败：

解决方法：

观察连接字符串中是否有这一句：

Integrated Security=True;

当为false时，将在连接中指定用户ID和密码。当为true时，将使用当前的Windows帐户凭据进行身份验证。

参考博客：https://blog.csdn.net/langwen2048/article/details/80116665?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.add_param_isCf&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.add_param_isCf

简化了大佬的做法，自己做的还是比较菜。数据库用的sql server。

登陆界面：

using System;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class login : Form
    {
        public login()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)//登陆按钮
        {

            String username, password;
            username = UserName.Text;
            password = Password.Text;
            String myconn = "Data Source=(Local);Initial Catalog=Cuser;User ID=sa;Password=tiancaiisme1;";//数据库实例连接字符串
            SqlConnection sqlConnection = new SqlConnection(myconn);//新建数据库连接实例
            sqlConnection.Open();//打开数据库连接
            String sql = "select UserName,Password from users where UserName='" + username + "'and Password='" + password + "'";//SQL语句实现表数据的读取
            SqlCommand sqlCommand = new SqlCommand(sql, sqlConnection);
            Console.WriteLine(Password);
            Console.WriteLine(sql);//控制台输出
            SqlDataReader sqlDataReader = sqlCommand.ExecuteReader();
            if (UserName.Text == "")
            {
                MessageBox.Show("请输入用户名", "登陆失败");
                UserName.Focus();
            }
            else if (Password.Text == "")
            {
                MessageBox.Show("请输入密码", "登陆失败");

            }
            else
            {
                if (sqlDataReader.HasRows)//满足用户名与密码一致，进入下一个界面
                {
                    //实现页面跳转
                    Form1 form3 = new Form1();
                    this.Hide();     //隐藏当前窗体   
                    form3.ShowDialog();
                    Application.ExitThread();   //退出当前窗体，这一步很重要，否则最后可能无法将所有进程关闭。最好是在跳转页面后，将之前的页面退出。
                }
                else//如果登录失败，询问是否注册新用户
                {
                    DialogResult dr = MessageBox.Show("是否注册新用户？", "登录失败", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
                    if (dr == DialogResult.Yes)//打开注册界面
                    {

                        register form2 = new register();
                        this.Hide();
                        form2.ShowDialog();
                        Application.ExitThread();
                    }
                    else
                    {
                        UserName.Text = "";
                        Password.Text = "";
                        UserName.Focus();
                        this.Show();
                    }
                }
            }
            sqlConnection.Close();
        }

        private void button2_Click(object sender, EventArgs e)     //单击注册按钮
        {

            register form2 = new register();
            this.Hide();
            form2.ShowDialog();
            Application.ExitThread();
        }

        private void Quit_Click(object sender, EventArgs e)    //单击退出按钮
        {
            Application.Exit();
        }
    }
}

注册界面：

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.Data.SqlClient;
using System.Windows.Forms;
using System.Security.Cryptography;

namespace WindowsFormsApp1
{
    public partial class register : Form
    {
        public register()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)//注册按钮
        {
            String username, password, repassword;
            username = textBox1.Text;
            password = textBox2.Text;
            repassword = textBox3.Text;
            if (textBox1.Text == "")
            {
                MessageBox.Show("请输入用户名", "注册失败");
                textBox1.Focus();
            }
            else if (textBox2.Text == "")
            {
                MessageBox.Show("请输入密码", "注册失败");
                textBox2.Focus();
            }
            else if (textBox3.Text == "")
                MessageBox.Show("请确认密码", "注册失败");
            else
            {
                String myConn = "Data Source=(Local);Initial Catalog=Cuser;User ID=sa;Password=tiancaiisme1;";
                SqlConnection sqlConnection = new SqlConnection(myConn);    //实例化连接对象  
                sqlConnection.Open();
                String sql = "select UserName from users where UserName='" + username + "'";//SQL语句实现表数据的读取
                SqlCommand sqlCommand = new SqlCommand(sql, sqlConnection);
                SqlDataReader sqlDataReader = sqlCommand.ExecuteReader();

                if (sqlDataReader.HasRows)
                {
                    sqlConnection.Close();
                    MessageBox.Show("该用户名已存在，请重新注册", "注册失败");
                    textBox1.Text = "";
                    textBox2.Text = "";
                    textBox3.Text = "";
                    textBox1.Focus();     //指定光标在哪个textBox处闪烁
                }
                else
                {
                    if (password == repassword)//两次输入的密码一致  
                    {
                        sqlConnection.Close();
                        string myConn2 = "Data Source=(Local);Initial Catalog=Cuser;User ID=sa;Password=tiancaiisme1;";
                        SqlConnection sqlConnection2 = new SqlConnection(myConn2);   //实例化连接对象  
                        sqlConnection.Open();

                        //password = GetMD5(password);
                        String sql2 = "INSERT INTO users(UserName,Password) VALUES('" + username + "','" + password + "')";//SQL语句向表中写入数据  
                        SqlCommand sqlCommand2 = new SqlCommand(sql2, sqlConnection);
                        sqlCommand2.ExecuteNonQuery();
                        sqlConnection2.Close();
                        DialogResult dr = MessageBox.Show("是否返回主界面", "注册成功", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
                        if (dr == DialogResult.Yes)//打开注册界面
                        {

                            login form2 = new login();
                            this.Hide();
                            form2.ShowDialog();
                            Application.ExitThread();
                        }
                        else
                        {
                            textBox1.Text = "";
                            textBox2.Text = "";
                            textBox3.Text = "";
                            this.Show();
                        }

                    }
                    else
                    {
                        MessageBox.Show("两次输入密码不一致", "错误信息");
                        textBox1.Text = "";
                        textBox2.Text = "";
                        textBox3.Text = "";
                    }
                }
            }

        }
        private void button2_Click(object sender, EventArgs e) //返回登陆按钮
        {
            login form3 = new login();
            this.Hide();
            form3.ShowDialog();
            Application.ExitThread();

        }


    }
}