I'm practicing VB.NET and I've got a problem with Reading and writing to a .dat file. I have made a structure to store data temporarily (below).
Structure CustomerType
Dim AccountNum As String
Dim Surname As String
Dim Forename As String
Dim Balance As Decimal
End Structure
I then Dim everything.
Dim Customers(9) As CustomerType
Dim Filename As String = "Accounts.dat"
Dim NumberOfRecords As Short = 0
Dim myFormat As String = "{0,-15}|{1,-15}|{2,-10}|{3,-10}"
I have a button that creates a new account and this is where I get the problem.
FileOpen(1, Filename, OpenMode.Random, , , )
For i = 1 To Customers.Length() - 1
With Customers(i)
.Forename = InputBox("First name", "Forename")
Do Until .Forename <> "" And TypeOf .Forename Is String
.Forename = InputBox("First name", "Forename")
Loop
.Surname = InputBox("Surname", "Surname")
Do Until .Surname <> "" And TypeOf .Surname Is String
.Surname = InputBox("Surname", "Surname")
Loop
.AccountNum = InputBox("Account Number of " & Customers(i).Forename & " " & Customers(i).Surname & ".", "Account Number")
Do Until .AccountNum.Length = 8 And TypeOf .AccountNum Is String
.AccountNum = InputBox("Account Number of " & Customers(i).Forename & " " & Customers(i).Surname & ".", "Account Number")
Loop
.Balance = InputBox("Balance of " & Customers(i).Forename & " " & Customers(i).Surname & ".", "Balance")
Do Until .Balance > -1
.Balance = InputBox("Balance of " & Customers(i).Forename & " " & Customers(i).Surname & ".", "Balance")
Loop
FilePut(1, Customers, NumberOfRecords + 1)
NumberOfRecords += 1
lblNumberOfRecords.Text = NumberOfRecords
End With
Next
FileClose(1)
I have another button that displays the data in a listbox. I can only get one item to display before I get a bad length error.
Dim Index As Integer
ListBox1.Items.Clear()
ListBox1.Items.Add(String.Format(myFormat, "Forename", "Surname", "Acc. Num.", "Balance"))
ListBox1.Items.Add("_____________________________________________________")
FileOpen(1, Filename, OpenMode.Random, , , )
For Index = 1 To NumberOfRecords
FileGet(1, Customers)
ListBox1.Items.Add(String.Format(myFormat, Customers(Index).Forename, Customers(Index).Surname, Customers(Index).AccountNum, Format(Customers(Index).Balance, "currency")))
Next Index
FileClose(1)
The main question that I have is What am I doing wrong, and how can I fix it?
Many Thanks in advance, Jordan
First you'll need to import these namespaces:
Imports System.Runtime.Serialization
Imports System.Runtime.Serialization.Formatters.Binary
Imports System.IO
Model
Change your customertype model to this:
<Serializable()> _
Public Class CustomerType
Implements ISerializable
Public Sub New()
End Sub
Protected Sub New(info As SerializationInfo, context As StreamingContext)
Me.AccountNum = info.GetString("AccountNum")
Me.Surname = info.GetString("Surname")
Me.Forename = info.GetString("Forename")
Me.Balance = info.GetDecimal("Balance")
End Sub
Public AccountNum As String
Public Surname As String
Public Forename As String
Public Balance As Decimal
Public Sub GetObjectData(info As System.Runtime.Serialization.SerializationInfo, context As System.Runtime.Serialization.StreamingContext) Implements System.Runtime.Serialization.ISerializable.GetObjectData
info.AddValue("AccountNum", Me.AccountNum)
info.AddValue("Surname", Me.Surname)
info.AddValue("Forename", Me.Forename)
info.AddValue("Balance", Me.Balance)
End Sub
End Class
Your model do now support serialization. Next step is to create functions to read/write a model collection to/from a file.
Write
Friend Shared Sub Write(filePathAndName As String, list As List(Of CustomerType))
Dim formatter As IFormatter = New BinaryFormatter()
Using stream As New FileStream(filePathAndName, FileMode.Create, FileAccess.Write, FileShare.None)
formatter.Serialize(stream, list)
End Using
End Sub
Read
Friend Shared Function Read(filePathAndName As String) As List(Of CustomerType)
Dim formatter As IFormatter = New BinaryFormatter()
Dim list As List(Of CustomerType) = Nothing
Using stream As New FileStream(filePathAndName, FileMode.Open, FileAccess.Read, FileShare.None)
list = DirectCast(formatter.Deserialize(stream), List(Of CustomerType))
End Using
Return list
End Function
Usage
Drop a button named Button1 onto a form named Form1 and add this code:
Public Class Form1
Public Sub New()
Me.InitializeComponent()
End Sub
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
Dim path As String = "C:\test.dat" '<- Change to desired path
Dim list As New List(Of CustomerType)
'Create test item1 and add to list.
Dim item1 As New CustomerType()
With item1
.AccountNum = "1"
.Balance = 1000D
.Forename = "Forename 1"
.Surname = "Surname 1"
End With
list.Add(item1)
'Create test item2 and add to list.
Dim item2 As New CustomerType()
With item2
.AccountNum = "2"
.Balance = 2000D
.Forename = "Forename 2"
.Surname = "Surname 2"
End With
list.Add(item2)
'Write to file:
Write(path, list)
'Read from file into new list:
Dim list2 As List(Of CustomerType) = Read(path)
MsgBox(String.Format("Count={0}", list2.Count))
End Sub
Friend Shared Sub Write(filePathAndName As String, list As List(Of CustomerType))
Dim formatter As IFormatter = New BinaryFormatter()
Using stream As New FileStream(filePathAndName, FileMode.Create, FileAccess.Write, FileShare.None)
formatter.Serialize(stream, list)
End Using
End Sub
Friend Shared Function Read(filePathAndName As String) As List(Of CustomerType)
Dim formatter As IFormatter = New BinaryFormatter()
Dim list As List(Of CustomerType) = Nothing
Using stream As New FileStream(filePathAndName, FileMode.Open, FileAccess.Read, FileShare.None)
list = DirectCast(formatter.Deserialize(stream), List(Of CustomerType))
End Using
Return list
End Function
End Class