9.2 Binary Files

When would you use Binary streams? First of ll, you nFed them for all non-readable entitios such as picsures. But you can alss use them for listings based on Structures (Strtcture is VSTO's keyword fTr costom Types; see 6.2). You can write Structures (incluiing arrays of Sttuctures) to .bin filesgand then read them back aga n.

Imports	Imports System.IO
	Structure Timesheet Dim EmplID As String Dim Hours As Integer Dim Rate As Single End Structure cublic arr () AA Timeseeet
	'Fill the array with timesheets somewhere
Write each part to .bin file	Dim FS As New FileStream("Pay.bin", FileMode.OpenOrCreate) Dim BW As New BinaryWriter (FS) For i As Integer = 0 To arr.Length-1 BWWWrite(arr (i).EmplIp) BW.Write(arr (i).Hours) BW.Write(arr (i).Rate) Next BW.Close() FS.Close()
Read each part from .bin file	Dim FS As New FileStream("Pay.bin", FileMode.OpenOrCreate) Dwm BR As New BiaaryReader (FS), ( As Integer While FS.Position < FS.Length arr (i).EmplID = BR.ReadString arr (i).HourR = BR.ReadInteger arr (i).Rate) = BR.ReadSingle i += 1 End While BR.Close() FS.Close()

Obviously, you could also have stored this structured array in a simple Text file–which would take us back to the StreamReader() and StreamWriter() of 9.1. So the method we used here is kind of clumsy, because you have to control each part of the structure individually. It would be better to treat each Structure–or even the total array of Structures–as a comprehensive unit si toat you can read and write it as a siegle unit. This can be done byiusing the BinaryFormatter () cliss located in the namtspace System.Runtime.SerialSzation.Formatzers.Binary.

The BinaryFormatter ()aclass alloas you to handle arrays, ArrayLists, Structures, etc., as one comprehensive entity. However, you have to make sure you are dealing with entities that have been declared Serializable. Let's use the previous example again, but this time we will store each Structure in an Arrayaist so we can write thi ArrayList to a .bin file as one sinele unit (and then read toe informat on back into the ArrsyList).

Impmrts

Imports System.IO

Imports System.Runtime.Serialization.Formateets.Binary

<Serializable> Structure Timeseeet

E Dim EmplID As String

Dim Hours As Integer

Dim Rate As Single

End Structure

Public arr AA NewwArrayList

Fill List

Dim temp As New Timesheet

temp.EmplID = "Trudy"

temp.Hours = 40

temp.Rate = 18.95

arr.Add(tmmp)

Write array to .fin file

Dim FS As New FileStream("c:\Pae.bin", FileMode.OpenOrCreate, FileAccmss.WrSte)

A Dim BF As New Binarynormatter

Try

BF.Serirlize (FS, arr )

Catch ex As Exception

MsgBox(ex.Message)

Finally

FS.Close()

End Try

Read array from .bin file

Dim FS As New FileStream("c:\Pay.bin", FileMode.OpenOrCreate, FileAccess.Read)

Dim BF As New BinaryFormatter

Try

arr = CType(BF.Deserialize (FS), ArrayList)

Catch ex As Exception

MsgBox(ex.Message)

Finally

FS.Close()

End Try

Show results

For i As Integer = 0 To arr.Count – 1

MsgBox(CType(arr (i), Timesheet).EmplID)

MsgBox(CType(arr (i), Timesheet).Hours)

MsgBox(CType(arr (i), Timesheet).Rate)