x69 x69 - 2 months ago 17
C# Question

C# : System.InvalidOperationException Error

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.

But After user logged in I saw the error like this :

enter image description here

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");
}
}

}
}


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();
}
}
}


If anyone find out the problem..help me to find it out please!

Answer

You need to open your sql connection instance first to make a query against sql server.

Change your code:

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);

//...