What is Collection in Visual Basic?

Collection in Visual Basic

Collection:

Visual Basic provides an alternative of an array in the form of collection. In case of array elements are accessed by its index number but elements of a collection are accessed by using key that is unique for each element and also by index number. A collection is declared as

            Dim CityName As New Collection

The word New tells Visual Basic to create new collection with CityName. The object provides four methods.

Add:

Add method is used to add new item in a collection syntax of Add Method is as under 

          Collection.Add Value, Key, Beforekey, Afterkey

The argument Value represents actual item to be added in a collection and key argument represents the key for storing item. Beforekey and Afterkey arguments represents the key before or after which new item is added, but one of them can be used at a time e.g.

           CityName.Add "D.I.Khan","key2","key1"

The item 'D.I.khan' is added in the CityName collection with key "key2" and before the element of key "key1"

Remove:

Remove method is used to delete an item from collection by using an index number or key value. e.g.

                     CityName.Remove (2)                'used of index number
                     CityNameRemove ("key2")       'used of key

Item:

Using index number or a key uses, Item method to return an item of the collection e.g.

 CityName.item(1)                           'refers to first item
 CityName.item("key2")         'refers to item with key "key2"

Count:

Count method is used to return the total items of a collection. e.g.

                CityName.Count          'refers to total elements of CityName collection


Examples:

Start Visual Basic with new Standard EXE project, place a CommandButton on a Form and set the properties of controls according to the following table.

Control Name	Property	Value
Form	WindowState	2-Maximized
Command1	Caption	Enter New CityName in Collection
Command2	Caption	Count total element in Collection
Command3	Caption	Remove an item From collection
Command4	Caption	View an item of Collection
Command5	Caption	View all elements of collection
Command6	Caption	View elements of Collection by using key

Create six buttons with the upper Names.

Write the following coding in Click events of each CommanButton control and in the Load event of the Form control and in General Section.

‘In General Section Dim CityName As New Collection Dim c As Integer

Private Sub Command1_Click ()      Dim cname As String      Cname = InputBox (“Enter New CityName”)       CityName.Add cname, “key” + CStir(c)        C = c + 1 End Sub

Private Sub Command2_Click () Print “Total Element in CityName = “CityName.Count End Sub

Private Sub Command3_Click ()       On error Resum Next        Dim index As String        Index = InputBox (“Enter index for delete the element”        If index < 1 0r index > CityName.Count Then                 MsgBox (“Invalid index number”)         Else          CityName.Remove (Val(index))         End If End Sub

Private Sub Command4_Click ()       On error Resum Next        Dim index As String        Index = InputBox (“Enter index for print  the element”        If index  = “” then         Exit Sub         End If         If Index < 1 or index > CityName.Count Then                 MsgBox (“Invalid index number”)         Else          Print CityName.Remove (Val(index))         End If End Sub

Private Sub Command5_Click ()     For Each cname in CityName             Print cname       Next End Sub

Private Sub Command6_Click ()       On error GoTo lab1        Dim key As String        key = InputBox (“Enter index for printed  the element”        If  key  = “” then         Exit Sub         End If         If  CityName.Count > 1 Then          Print CityName.item (Key)           Else             Print “No Element Exist”         End If          Exit Sub Lab1:             MsgBox (“Key Not Valid”) End Sub

Press F5 to run this project and press each CommandButton to check its output.

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Posted in: Visual Basic