c#：如何从数据库中获取数据并传递给另一个表单？答案

【问题标题】：c# : How to get data from database and pass to another form?c#：如何从数据库中获取数据并传递给另一个表单？
【发布时间】：2016-10-02 06:07:19
【问题描述】：

我正在构建一个桌面应用程序，当用户在新登录时，他的 ID 将出现在文本框中。但在我的情况下，查询运行成功，但 id 没有出现在 textBox.. 谁能帮我找出来吗？

用户登录的第一种形式（Form1.cs）

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;


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

        public string employeeID;
        private void exitButton_Click(object sender, EventArgs e)
        {
            this.Close();
        }
        private void loginButton_Click(object sender, EventArgs e)
        {
            SqlConnection connection = new SqlConnection(@"Data Source=INCEPSYS-SE\TEST;Initial Catalog=Employee;Integrated Security=True");
            connection.Open();
            String query = "select * from Employees where Name = '" + nameTextBox.Text + " ' and Password = '" + passwordTextBox.Text + "'";

            SqlCommand command = new SqlCommand(query, connection);
            SqlDataReader myReader = command.ExecuteReader();
            while (myReader.Read())
            {
                string employeeID = myReader["EmployeeID"].ToString();
            }
            myReader.Close();
            SqlDataAdapter sda  = new SqlDataAdapter(query,connection);            
            connection.Close();
            DataTable dt = new DataTable();
            sda.Fill(dt);
                if (dt.Rows.Count == 1)
            {
                this.Hide();
                Entry ss = new Entry(employeeID);
                ss.Show();
            }
            else
            {
                MessageBox.Show("Please Check your Username & password");
            }
        }

    }
}

第二种形式（Entry.cs）

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;

namespace EmployeeApp
{
    public partial class Entry : Form
    {
        public Entry()
        {
            InitializeComponent();
        }
        public Entry(string employeeId)
        {
              InitializeComponent();
              idTextBox.Text = employeeId;
        }


       private void reportButton_Click(object sender, EventArgs e)
        {
            Report report = new Report();
            report.Show();
        }
    }
}

【问题讨论】：

标签： c# winforms desktop-application

【解决方案1】：

删除局部变量声明，因为employeeID 是一个全局变量并且已经首先声明，所以当您使用string 为其添加前缀时，它会创建另一个在此范围之外无法访问的局部变量

while (myReader.Read())
  {
      employeeID = myReader["EmployeeID"].ToString();
  }

【讨论】：

【解决方案2】：

你有一个局部变量。您可以像这样更正和优化您的代码：

    private void loginButton_Click(object sender, EventArgs e)
    {
        //If use set quote into your textbox
        string name = nameTextBox.Text.Replace("'", "''");
        string pass = passwordTextBox.Text.Replace("'", "''");

        String query = string.Format("select * from Employees where Name = '{0}' and Password = '{1}'", name, pass);
        string employeeID = "";


        using (SqlConnection connection = new SqlConnection(@"Data Source=INCEPSYS-SE\TEST;Initial Catalog=Employee;Integrated Security=True"))
        {
            connection.Open();

            using (SqlDataAdapter sda = new SqlDataAdapter(query, connection))
            {
                DataTable dt = new DataTable();
                sda.Fill(dt);

                if (dt.Rows.Count > 0)
                {
                    employeeID = dt.Rows[0]["EmployeeID"].ToString();
                    this.Hide();
                    Entry ss = new Entry(employeeID);
                    ss.Show();
                }
                else
                {
                    MessageBox.Show("Please Check your Username & password");
                }

                dt.Dispose();

            }
        }



    }

【讨论】：