How to get rid of Conversion from string "admin" to type 'Double' is not valid

Question

Hello guys am having issues with my login form for multiple users of my software, below is the complete login button code for the admin

Private Sub btnlogin_Click(sender As System.Object, e As System.EventArgs) Handles btnlogin.Click
    If cmbusertype.Text = "" Then
        MsgBox("Please select the appropriate Account Type!", vbExclamation, "Account Type")
    End If
    If cmbusertype.Text = "Admin" Then
        Dim Strconn As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\phermacy.mdf;Integrated Security=True;User Instance=True"
        Dim Selectcmd As String = "select * from tbl_admin where admin_username = '" + txtusername.Text + "' and password = '" + txtpassword.Text + "'"
        Dim da As New SqlDataAdapter
        Dim ds As New DataSet
        Dim sqlcmd As SqlCommand
        sqlconn = New SqlConnection(Strconn)
        Try
            sqlconn.Open()
        Catch ex As Exception
            MsgBox("Could not connect to DataBase. Application will close now!", vbCritical, "Database Error")
            End
        End Try
        sqlcmd = New SqlCommand(Selectcmd, sqlconn)
        da.SelectCommand = sqlcmd
        sqlcmd.Dispose()
        sqlconn.Close()
        da.Fill(ds)

Matching Admin User Name & Password

 If ds.Tables(0).Rows.Count > 0 Then

                    If txtusername.Text = ds.Tables(0).Rows(0).Item(0) And txtpassword.Text = ds.Tables(0).Rows(0).Item(1) Then
                        MsgBox("Administrator Log-in Successful.", vbInformation, "Admin Log-in")
                        Me.Hide()
                        adminform.Show()

                    Else
                        ErrorProvider1.SetError(txtusername, "Invalid User Name.")
                        ErrorProvider1.SetError(txtpassword, "Invalid Password.")
                        MsgBox("Invalid Administrator Username or Password.", vbCritical, "Admin Log-in")
                    End If

                Else
                    ErrorProvider1.SetError(txtusername, "Invalid User name or Password.")
                    ErrorProvider1.SetError(txtpassword, "Invalid User name or Password.")
                    ErrorProvider1.SetError(cmbusertype, "Please select the appropriate Account Type")
                    MsgBox("Invalid Administrator Username or Password.", vbCritical, "Admin Log-in")
                End If
            End If
        End Sub

the code line highlighted is the following

        If txtusername.Text = ds.Tables(0).Rows(0).Item(0) And txtpassword.Text = ds.Tables(0).Rows(0).Item(1) Then

and the error is "Conversion from string "admin" to type 'Double' is not valid." am actually new to vb trying to create a login for multiple users, the above part as you can see is just for the admin. Please any help here will be appreciated thanks.

Answer 1

试试这个......

   Private Sub btnlogin_Click(sender As System.Object, e As System.EventArgs) Handles btnlogin.Click
    If cmbusertype.Text = "" Then
        MsgBox("Please select the appropriate Account Type!", vbExclamation, "Account Type")
    End If
    If cmbusertype.Text = "Admin" Then
        Dim Strconn As String = "Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\phermacy.mdf;Integrated Security=True;User Instance=True"
        Dim Selectcmd As String = "select * from tbl_admin where admin_username = @usernme and password = @paswd"
        Dim da As New SqlDataAdapter
        Dim ds As New DataSet
        Dim sqlcmd As SqlCommand
        sqlconn = New SqlConnection(Strconn)
        Try
            sqlconn.Open()
        Catch ex As Exception
            MsgBox("Could not connect to DataBase. Application will close now!", vbCritical, "Database Error")
            End
        End Try
        sqlcmd = New SqlCommand(Selectcmd, sqlconn)
        sqlcmd.parameters.addwithValue("@usernme",txtusername.Text)
        sqlcmd.parameters.addwithValue("@paswd",txtpassword.Text)
        da.SelectCommand = sqlcmd
        sqlcmd.Dispose()
        sqlconn.Close()
        da.Fill(ds)