An exception of type 'System.InvalidOperationException' occurred in System.Data.dll - vb.net

Question

This is my code. help me to solve it thanks!
An exception of type 'System.InvalidOperationException' occurred in System.Data.dll but was not handled in user code Additional information: ExecuteReader requires an open and available Connection. The connection's current state is closed
Imports System.Data.SqlClient
Partial Class Staff
Inherits System.Web.UI.Page
' Dim conn As New SqlConnection("Data Source=USER-PC\SQLEXPRESS;Initial Catalog=carrental;Integrated Security=True;Pooling=False")
Dim con As New Data.SqlClient.SqlConnection
Dim cmd As New Data.SqlClient.SqlCommand
Dim dr As Data.SqlClient.SqlDataReader
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Try
con.ConnectionString = ("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\user\Desktop\oh manisku\PROJECT ABIS\project baru\project baru\App_Data\order.mdf;Integrated Security=True;Connect Timeout=30")
con.Open()
Catch ex As Exception
' MsgBox(ex.Message)
End Try
End Sub
Protected Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
cmd.CommandText = ("Select Username, Password from Admin WHERE Username ='" & txtusername.Text & "' and Password = '" & txtPass.Text) & "' "
cmd.Connection = con
dr = cmd.ExecuteReader
con.Close()
If dr.HasRows Then
MsgBox("Succesfully Login")
Response.Redirect("recalled.aspx")
Else
MsgBox("Invalid Username and Password")
End If
End Sub
Private Sub btnReset_Click(sender As Object, e As EventArgs) Handles btnReset.Click
End Sub
Protected Sub SqlDataSource1_Selecting(sender As Object, e As SqlDataSourceSelectingEventArgs) Handles SqlDataSource1.Selecting
End Sub
End Class

Answer 1

As I said in my comment, you're closing the connection before reading the data. You should move the connection close to after you finished with the data reader.
Protected Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
Dim con As New Data.SqlClient.SqlConnection
con.ConnectionString = ("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\user\Desktop\oh manisku\PROJECT ABIS\project baru\project baru\App_Data\order.mdf;Integrated Security=True;Connect Timeout=30")
con.Open()
cmd.CommandText = ("Select Username, Password from Admin WHERE Username ='" & txtusername.Text & "' and Password = '" & txtPass.Text) & "' "
cmd.Connection = con
dr = cmd.ExecuteReader
If dr.HasRows Then
MsgBox("Succesfully Login")
Response.Redirect("recalled.aspx")
Else
MsgBox("Invalid Username and Password")
End If
dr.Close() ' close the datareader
con.Close() ' close the connection
End Sub
Private Sub btnReset_Click(sender As Object, e As EventArgs) Handles btnReset.Click
End Sub
Calling ExecuteReader simply opens the stream. If you close the connection, you close the stream. To use a telephone analogy: it's like hanging up on someone, and then trying to have a conversation.
Please also switch to using parameterized queries since, as it stands, I could enter my username as ' OR 1 = 1 ; -- and I'd gain full access to the first account in your system.
Also, please look into ways to securely store passwords. You should never store passwords in your database in plain text, and you should never store passwords in a way that allows you to reverse them to the original user input. Passwords should be hashed with a salt. see here.