Carman Neustaedter - VB .Net Example

File I/O and Array Lists Example

These instructions will build an example program that looks like this:

The new button creates an empty record. The save button will update the current record being viewed. The delete button will remove the current record being viewed. You can search for records by typing a person's name in the Search box; the results are shown dynamically while the user types in a search word.

Download the code by clicking on the Zip file.

Instructions for Creating the Example:

Start Visual Studio from the Start menu.
Click on the New Project button in the bottom of the screen.
Select Visual Basic Projects, and Windows Application. In the Name box give your project a name.
Layout your form like this:

The textboxes are called txtName, txtPhone, and txtSearch. The buttons are called cmdNew, cmdSave, and cmdDelete. The listbox is called lstResults.

5. At the top of your code add these two lines:

' an ArrayList is like a vector, you can add and remove elements, and it will resize automatically
' start it out with size 10
Dim myAddressBook As New ArrayList(10)
' keeps track of the record currently being viewed
Dim currentID As Integer

6. Add an import statement to the very top of your code window to easily access File I/O classes:

' this contains the StreamWriter and StreamReader classes
Imports System.IO

7. Create a new class named Person. Right click on your Project in the Solution Explorer and choose Add and then Add Class from the context menu. Choose the name Person.vb for your class file.

8. Our class will contain fields for a record, much like a database table. In your class, type this code:

Public Class Person
    Public ID As Integer
    Public Name As String
    Public Phone As String
End Class

9. We'll now write three functions to handling the creation, updating, and deletion of records. The first will create new records, the second will update/save records, and the third will delete records. Later, we will use these in the events for our buttons. Place these three functions into your code:

Private Function CreateNewRecord() As Integer
    ' add a new record to our ArrayList, the function will return the ID number
    ' associated with the new record

   ' create a new object of type Person
    Dim p As New Person

    ' return the ID number of the new record
    CreateNewRecord = myAddressBook.Count + 1
   ' set the record ID for the new record
    p.ID = myAddressBook.Count + 1
' add the record to the array list
    myAddressBook.Add(p)
End Function

Private Function UpdateRecord(ByVal currentID As Integer, ByVal Name As String, ByVal Phone As String)
    ' update a record with the given ID number using the Name and Phone # parameters

    ' create a new object of type Person
    Dim p As New Person

    ' find the record to update using the ID number
    For Each p In myAddressBook
        If p.ID = currentID Then
            Exit For
        End If
    Next
    ' update the record
    p.Name = Name
    p.Phone = Phone

End Function

Private Function DeleteRecord(ByVal currentID As Integer)
    ' remove a record matching the parameter CurrentID from the array list

' create a new object of type Person
    Dim p As New Person

    ' find the record to delete
    For Each p In myAddressBook
        If p.ID = currentID Then
            Exit For
        End If
    Next
' delete the record
    myAddressBook.Remove(p)

End Function

10. Create two functions: one to write out records to a file from memory, and one to read records from a file into memory.

Private Function SaveRecords()
    ' write out the contents of the array list to a file

    ' create a new object of type Person
    Dim p As New Person
    ' open a file for output, I use false because I don't want to append to the file
    Dim sw As New StreamWriter("addressbook.txt", False)

    ' write out the contents of each item in the array list
    For Each p In myAddressBook
        sw.WriteLine(p.Name)
        sw.WriteLine(p.Phone)
    Next
    ' close the file
    sw.Close()

End Function

Private Function ReadRecords()
    ' read in all entries from the file to an array list

    ' check that our file exists
    If File.Exists("addressbook.txt") Then
        ' open a file for input
        Dim sr As New StreamReader("addressbook.txt")
        ' check if there are more records to get
        ' Peek will check the next available character but not consume it
        Do Until sr.Peek = -1
           ' create a new empty record
            currentID = CreateNewRecord()
            ' put the name and phone # into the new record
            UpdateRecord(currentID, sr.ReadLine, sr.ReadLine)
        Loop
        ' close the file
        sr.Close()
    End If
End Function

11. Double click on your form to create a Form1_Load event. Add this code to it so you can move the records from your file into the program's memory. We also start the program with a new empty record.

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
   ' load all the records into the array list
    ReadRecords()
   ' create a blank record to start with
    currentID = CreateNewRecord()
End Sub

12. Create a click event for the cmdNew button by double clicking on it. Add this code:

Private Sub cmdNew_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdNew.Click
    currentID = CreateNewRecord()

' clear the fields
    txtName.Text = ""
    txtPhone.Text = ""
End Sub

13. Create a click event for the cmdSave button by double clicking on it. Add this code:

Private Sub cmdSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdSave.Click
    ' update the record that has the same ID number
    UpdateRecord(currentID, txtName.Text, txtPhone.Text)
    ' write out the records in the array list to a file
    SaveRecords()
End Sub

14. Create a click event for the cmdDelete button by double clicking on it. We will leave a new empty record after we delete the record. Add this code:

Private Sub cmdDelete_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdDelete.Click
' delete the record matching the current ID number
    DeleteRecord(currentID)
' clear text boxes
    txtName.Text = ""
    txtPhone.Text = ""
    txtSearch.Text = ""
' start with an empty record
    currentID = CreateNewRecord()
    ' write out the records to a file
    SaveRecords()
End Sub

15. Create a TextChanged event for the txtSearch textbox so that when someone types their keyword, the search results will update. Add this code:

Private Sub txtSearch_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtSearch.TextChanged
    ' search the array list for matching records as the user types

    ' create an object of type Person
    Dim p As New Person
    ' clear the results box
    lstResults.Items.Clear()
    ' only search if the person has typed something in
    If txtSearch.Text <> "" Then
        ' do a linear search through the array list
        For Each p In myAddressBook
            ' try a partial string match, looking at the first few letters of each name
            If Mid(p.Name, 1, Len(txtSearch.Text)) = txtSearch.Text Then
                ' if there's a match, stick the name in the results list
                lstResults.Items.Add(p.Name)
            End If
        Next
    End If
End Sub

16. When the user clicks on a search result, it will appear in the main textboxes. Create a click event for the lstResults listbox.

Private Sub lstResults_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles lstResults.Click
    ' show the selected item in the list box

    ' create an object of type person
    Dim p As New Person
    ' make sure something is selected in the listbox
    If lstResults.SelectedIndex <> -1 Then
        ' do a linear search through the array list to find the record to display
        For Each p In myAddressBook
            ' look for a name match
            If p.Name = lstResults.Items(lstResults.SelectedIndex) Then
                Exit For
            End If
        Next
       ' load the record
        txtName.Text = p.Name
        txtPhone.Text = p.Phone
      ' save the ID in case we want to update
        currentID = p.ID
    End If
End Sub