VB6 Tutorial 54: Collections

Posted On 2018-05-27 by VB6Boy
Keywords: visual,basic,vb6,visualbasic,tutorial,basic,beginner
Tags: VB6 Tutorials 
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Collections are objects in Visual Basic that are used to store a group of data values. Collections are similar to array. But there are some special features that differentiate the collections from arrays.

We have seen that array elements must be of the same data type. But the Collection members can be of any data type and you don't need to set the size of the Collection object. You can easily add items to the collection and it will grow accordingly.

Creating a Collection

To use a Collection in your code, you first need to declare and create it.

Example

Dim names As Collection     'Declaring the Collection
Set names = New Collection   'Creating the Collection

Or, replace the above code with this one line code

Dim names As New Collection   'Declaration and creation

The Add method

You can add one item at a time using the Add method.

Example

Dim names As New Collection
names.Add "john"
names.Add "david"

You may use a string key associated with the item. The string key is used to refer to a Collection item.

Dim names As New Collection
names.Add "John", "one"   ' "one" is the string key, used to refer to the item

The Item method

You can refer to a particular item of the collection using the Item method. Here you may use either the index or key value. The index value starts from 1.

Syntax

Collection_Name.Item(Index)

or

Collection_Name.Item(Key)

Example

Retrieving a particular item using the index of the item

Private Sub cmdShow_Click()
    Dim names As New Collection

    names.Add "John", "one"
    names.Add "David"

    Print names.Item(2) '2 is the index of the item

End Sub

Output

David

Example

Retrieving a particular item using the string key of the item

Private Sub cmdShow_Click()
    Dim names As New Collection

    names.Add "John", "one"
    names.Add "David"

    Print names.Item("one")

End Sub

Output

John

The Item method is the default member of the Collection class, so you may omit it in your code.

Example

Private Sub cmdShow_Click()
    Dim names As New Collection

    names.Add "John", "one"
    names.Add "David"

    Print names("one")
    Print names(2)

End Sub

Output

John
David

Before and After

You can choose to store the item values exactly where you want using the Before and After argument of the Add method.

Example

Private Sub cmdShow_Click()

     Dim items As New Collection

     items.Add "one"
     items.Add "two"
     items.Add "three", , 1

     For i = 1 To 3
        Print items.Item(i)
     Next i
End Sub

Output

three
one
two

Remove

You can remove a particular item from the Collection using the Remove method.

Example

Private Sub Command1_Click()
     Dim country As New Collection
     country.Add "USA"
     country.Add "UK"
     country.Add "Japan", "j"

     country.Remove (1)
     country.Remove ("j")

End Sub

Count

Example

Private Sub cmdCount_Click()
     Dim country As New Collection
     country.Add "USA"
     country.Add "India"
     country.Add "Japan", "j"

     Dim n As Integer
     n = country.Count
     Print n

End Sub

Output

3

Retrieving the last item

Example

Private Sub Command1_Click()
     Dim country As New Collection
     country.Add "Germany"
     country.Add "India"
     country.Add "China", "j"

     Print country.Item(country.Count)
End Sub

Output

China

Delete all items

Use a Do While loop to delete all item from the Collection object.

Example

Private Sub cmdDeleteAll_Click()
     Dim country As New Collection
     country.Add "Bangladesh"
     country.Add "Australia"
     country.Add "Russia", "j"

     Do While (country.Count > 0)
        country.Remove 1
     Loop

     Print country.Count
End Sub

Output

0

Another way to delete all items is to destroy the Collection object. The following code destroys the Collection object and thus deletes all the items.

Set items = Nothing

Or

Set items = New Collection

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