vb collection data structures

VB Collection Data Structures

• Array

• ArrayList

• HashTable

• VB6 Collection

• Others:SortedList, Stack, Queue

Arrays

Declaring a Array

• With subscript:– Dim numbers(2) as Integer– Using variable as subscript:

• Dim arrayIndex as Integer = 10• Dim myArray(arrayIndex) as Integer

• Without subscript– Dim numbers() as Integer = {2, 4, 6}– Dim someNames() as String = {“”, “”, “”}

• Note: Can not have a subscript with a initialization list. • Without subscript and initialization

– Dim numbers As Integer()– numbers = New Integer() {2, 4, 6}

Accessing Array Elements with a For … Next Loop

– Dim i As Integer = 0, sum As Integer = 0– For i = 0 To 2– sum += numbers(i)– Next

• GetUpperBound– For i = 0 to numbers.GetUpperBound(0)

sum += numbers(i)

– Next

• Length– For i = 0 to numbers.length-1

sum += numbers(i)

– Next

Accessing Array Elements with a For Each Loop

Dim i As Integer

For Each i In numbers

i = i * 2

MessageBox.Show(i.ToString)

Next

Array’s Properties and Methods• Properties:

– Length– IsFixedSize– IsReadOnly

• Methods– BinarySearch *** return negative value if not found– Clear– Clone, Copy, CopyTo– GetLowerBound, GetUpperBound– Reverse– Sort

Highest Values in a Array

Dim highest As Integer

highest = numbers(0)

For i = 1 To numbers.GetUpperBound(0)

If numbers(i) > highest Then

highest = numbers(i)

End If

Next

Searching ArraysDim found As Boolean = False

Dim searchValue As Integer

searchValue = InputBox("Enter search value: ")

For i = 0 To numbers.GetUpperBound(0)

If numbers(i) = searchValue Then

found = True

Exit For

End If

Next

If found Then

MsgBox("Number found")

Else

MsgBox("Number not found")

End If

Searching with the IndexOf Method

If numbers.IndexOf(numbers, InputBox("Enter search value: ")) < 0 Then

MessageBox.Show("not exist")

Else

MessageBox.Show("exist")

End If

Using Parallel Relationship between Array and Listbox

Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

ListBox1.Items.Add("Peter")

ListBox1.Items.Add("Paul")

ListBox1.Items.Add("Mary")

phone(0) = "1234"

phone(1) = "6789"

phone(2) = "3456"

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

MessageBox.Show(ListBox1.SelectedItem & "phone is" & phone(ListBox1.SelectedIndex))

End Sub

ReDim

• ReDim numbers(5) – Original values in the array will be lost.

• ReDim Preserve numbers(5)• Use ReDim to assign size if the array is

declared without subscript.– Dim test As Integer()– …– ReDim test(2)

Passing Arrays as ArgumentsDim outstr As String

setnew(test)

For i = 0 To test.GetUpperBound(0)

outstr &= test(i).ToString & vbCrLf

Next

MessageBox.Show(outstr)

End Sub

Sub setnew(ByVal a() As Integer)

Dim i As Integer

For i = 0 To a.GetUpperBound(0)

a(i) = 0

Next

End Sub

Note: ByVal or ByRef? With ByVal, it will prevent an array argument from being assigned to another array.

Two-Dimensional Arrays

– Depts=1– Prods=2– Dim SalesData(Depts, Prods) As Double

• With initialization– Dim SalesData(,) as Double = {{20,30,15},{40,32,55}}

For Each Loops for 2-dimensional Array

Dim salesData(,) As Double = {{20, 15, 30}, {30, 21, 50}}

Dim totalSales, I As Double

For Each I In salesData

totalSales += I

Next

TextBox1.Text = totalSales.ToString

For Next Loops for 2-dimensional Array

Dim row, col As Integer

For row = 0 To salesData.GetUpperBound(0)

For col = 0 To salesData.GetUpperBound(1)

totalSales += salesData(row, col)

Next

Next

MessageBox.Show(totalSales.ToString)

Problem: How to compute total sales by Department? by Product?

Data Binding with Arrays

• Connect a control to one data source.

• Arrays can be used as data source for a control.

• Demo: ListBox DataSource property.– Dim fruits() As String = {"Apple", "Orange",

"Banana", "Strawberry", "Kiwi"}– ListBox1.DataSource = fruits

Other Collections

• More flexible than array:– No need to declare the number of objects in a

collection.– Objects can be added, deleted at any position.– Object can be retrieved from a collection by a

key.– Can store any types of data.

ArrayList

• Define an arraylist:– Dim myArrayList As New ArrayList()

• Properties:Count, Item, etc.– myArrayList.Item(0) 0-based index

• Methods:– Clear, Add, Insert, Remove, RemoveAt,

Contains, IndexOf, etc.

ArrayList Demo

Dim testArrayList As New ArrayList()

Dim Fruits() As String = {"Apple", "orange", "Banana"}

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

Dim f2 As New Form2()

testArrayList.Add("David")

testArrayList.Add(20)

testArrayList.Add(Fruits)

testArrayList.Add(f2)

TextBox1.Text = testArrayList.Item(0)

TextBox2.Text = testArrayList.Item(1).ToString

TextBox3.Text = testArrayList.Item(2)(1)

TextBox4.Text = testArrayList.Item(3).Age

End Sub

For Each Loop with ArrayList

Dim testArrayList As New ArrayList()

Dim f2 As New DataForm2()

Dim Fruits() As String = {"Apple", "orange", "Banana"}

testArrayList.Add("David")

testArrayList.Add(20)

testArrayList.Add(Fruits)

testArrayList.Add(f2)

Dim myObj As Object

For Each myObj In testArrayList

MessageBox.Show(myObj.GetType.ToString)

Next

Data Binding with ArrayLists

• Arraylists can be used as data source for a control.

• Demo: ListBox DataSource property.– Dim myArrayList As New ArrayList()– myArrayList.Add("apple")– myArrayList.Add("banana")– myArrayList.Add("orange")– ListBox1.DataSource = myArrayList

Dim wordList As New ArrayList Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load wordList.Add("This") wordList.Add("is") wordList.Add("a") wordList.Add("list") wordList.Add("of") wordList.Add("words") wordList.Add("that") wordList.Add("we") wordList.Add("will") wordList.Add("use") wordList.Add("in") wordList.Add("the") wordList.Add("spell") wordList.Add("checker") wordList.Add("david") wordList.Add("chao") wordList.Add(" ") End Sub

Spelling Checker Example

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Try Dim re As Regex re = New Regex("\w+") Dim source As String source = txtSource.Text Dim mc As MatchCollection = re.Matches(source) Dim m As Match Dim result As String For Each m In mc If Not wordList.Contains(m.Value) Then result += m.ToString & vbCrLf txtSource.Select(txtSource.Text.IndexOf(m.ToString), m.Length) MessageBox.Show("next") End If Next MessageBox.Show("Invalid words: " & vbCrLf & result) Catch ex As System.Exception MessageBox.Show(ex.Message) End Try End Sub

HashTable• The HashTable collection provides very fast look-

up.• Each element in a HashTable is a DictionaryEntry

type containing a pair of Key and Value.• Properties:Count, Item, Keys, Values

– myHashTable.Item(key)

• Methods:– Clear, Add, Remove,ContainsKey, ContainsValue, etc.

• Note 1: Elements in a HashTable are stored according to the hash value of keys.

• Note 2: Keys must be unique.

HashTable ExampleDim myHashTable As New Hashtable()

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

myHashTable.Add("UK", "United Kingdom")

myHashTable.Add("US", "United States")

myHashTable.Add("CHN", "China")

myHashTable.Add("DE", "Germany")

Dim myKey As String

For Each myKey In myHashTable.Keys

ListBox1.Items.Add(myKey)

Next

End Sub

Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

MessageBox.Show(myHashTable.Item(ListBox1.SelectedItem))

End Sub

Dim searchKey As StringsearchKey = InputBox("enter key")If myHash.ContainsKey(searchKey) Then TextBox1.Text = myHashTable.Item(searchKey)Else MessageBox.Show("key not exists")End If

VB 6 Collections• Define a collection:

– Ex. Dim Pets as New Collection

• Methods:– ADD: Add object to a collection

• Pets.Add(“dog”)• Add an object with a key:

– Pets.Add(“Dog”, “D”)

– Item: Retrieve an object from a collection with a position index (base 1) or with a key.

• petName = Pets.Item(1)• petName = Pets.Item(“D”)

– Count: Return the number of objects in a collection.– Remove: Delete an object with a position index or key.

Iterating Through a CollectionDim Pets as New Collection

…

Dim Indx as Long

For Indx = 1 to Pets.Count

…operations …

Next Indx

For Each pet in Pets

… operations …

Next pet

Timer

• Event:– Tick

• Property:– Enable

– Interval property• measured in millisecond, 1000 millis = 1 second

• Methods:– Start

– Stop

Status Bar & Timer

• Status Bar– Panels property (collection)– Set ShowPanel property to true.– StatusBar1.ShowPanels = True

– StatusBarPanel1.Text = System.DateTime.Now.ToString

• Timer– Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal

e As System.EventArgs) Handles Timer1.Tick StatusBarPanel1.Text = System.DateTime.Now.ToString

End Sub

Bitmap Data Type

• To read a picture file to program:– Dim pic as New Bitmap(“c:\mypic.jpg”)

Rotate Form’s Background Image

Create a collection of pictures:

Dim pcol As New ArrayList

Add images to collection

Dim im1 As New Bitmap("c:\Paradise.jpg")

Dim im2 As New Bitmap("c:\Flyaway.jpg") Dim im3 As New Bitmap("c:\SnowTrees.jpg") pcol.Add(im1) pcol.Add(im2) pcol.Add(im3)

Use Timer to change image

Dim pcol As New ArrayList Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim im1 As New Bitmap("c:\Paradise.jpg") Dim im2 As New Bitmap("c:\Flyaway.jpg") Dim im3 As New Bitmap("c:\SnowTrees.jpg") pcol.Add(im1) pcol.Add(im2) pcol.Add(im3) End Sub

Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick Static counter As Integer Me.BackgroundImage = pcol.Item(counter) counter += 1 counter = (counter Mod 3) End Sub