C#:System.InvalidOperationException错误 [英] C# : System.InvalidOperationException Error
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问题描述
我正在构建一个方案为的桌面应用程序.一个用户将被登录,并且其ID的另一种形式将显示在文本框中.
I'm building a desktop application where the scenario is A user will be logged in and in another form it's id will be shown in text box.
但是在用户登录后,我看到了这样的错误:
But After user logged in I saw the error like this :
这是我的第一个表格(Form1.cs)
Here is my first form (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();
}
private 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");
SqlCommand command = new SqlCommand("select * from Employees where Name = '" + nameTextBox.Text + " ' and Password = '" + passwordTextBox.Text + "'", connection);
SqlDataReader myReader = command.ExecuteReader();
while (myReader.Read())
{
string employeeID = myReader["EmployeeID"].ToString();
}
SqlDataAdapter sda = new SqlDataAdapter("select count(*) from Employees where Name = '" + nameTextBox.Text + " ' and Password = '" + passwordTextBox.Text + "'", connection);
DataTable dt = new DataTable();
sda.Fill(dt);
if (dt.Rows[0][0].ToString() == "1")
{
this.Hide();
Entry ss = new Entry(employeeID);
ss.Show();
}
else
{
MessageBox.Show("Please Check your Username & password");
}
}
}
}
这是我的第二个表单(Entry.cs),我要在其中打印用户ID:
And Here is my Second form(Entry.cs) where I want to print the user id:
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(string employeeId)
{
InitializeComponent();
idTextBox.Text = employeeId;
}
private void reportButton_Click(object sender, EventArgs e)
{
Report report = new Report();
report.Show();
}
}
}
如果有人发现了问题..请帮助我找出问题!
If anyone find out the problem..help me to find it out please!
推荐答案
您需要先打开sql连接实例才能对sql服务器进行查询.
You need to open your sql connection instance first to make a query against sql server.
更改您的代码:
SqlConnection connection = new SqlConnection(@"Data Source=INCEPSYS-SE\TEST;Initial Catalog=Employee;Integrated Security=True");
connection.Open();
SqlCommand command = new SqlCommand("select * from Employees where Name = '" + nameTextBox.Text + " ' and Password = '" + passwordTextBox.Text + "'", connection);
//...
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