Lists

Syntax

  • List.Add(item As Type)
  • List.RemoveRange(index As Integer, count As Integer)
  • List.Remove(index As Integer)
  • List.AddRange(collection)
  • List.Find(match as Predicate(of String))
  • List.Insert(index as Integer , item as Type)
  • List.Contains(item as Type)

Add items to a List

Dim aList as New List(Of Integer)
aList.Add(1)
aList.Add(10)
aList.Add(1001)

To add more than one item at a time use AddRange. Always adds to the end of the list

Dim blist as New List(of Integer)
blist.AddRange(alist) 


Dim aList as New List(of String)
alist.AddRange({"one", "two", "three"}) 

In order to add items to the middle of the list use Insert

Insert will place the item at the index, and renumber the remaining items

Dim aList as New List(Of String)
aList.Add("one")
aList.Add("three")
alist(0) = "one"
alist(1) = "three"
alist.Insert(1,"two")

New Output:

alist(0) = "one"       
alist(1) = "two"
alist(2) = "three"

Check if item exists in a List

    Sub Main()
        Dim People = New List(Of String)({"Bob Barker", "Ricky Bobby", "Jeff Bridges"})
        Console.WriteLine(People.Contains("Rick James"))
        Console.WriteLine(People.Contains("Ricky Bobby"))
        Console.WriteLine(People.Contains("Barker"))
        Console.Read 
    End Sub

Produces the following output:

False
True
False

Create a List

Lists can populated with any data type as necessary, with the format

Dim aList as New List(Of Type)

For example:

Create a new, empty list of Strings

Dim aList As New List(Of String)

Create a new list of strings, and populate with some data

VB.NET 2005/2008:

Dim aList as New List(Of String)(New String() {"one", "two", "three"})

VB.NET 2010:

Dim aList as New List(Of String) From {"one", "two", "three"}

--

VB.NET 2015:

Dim aList as New List(Of String)(New String() {"one", "two", "three"})

NOTE:

If you are receiving the following when the code is ran:

Object reference not set to an instance of an object.

Make sure you either declare as New i.e. Dim aList as New List(Of String) or if declaring without the New, make sure you set the list to a new list - Dim aList as List(Of String) = New List(Of String)

Loop trough items in list

Dim aList as New List(Of String)
aList.Add("one")
aList.Add("two")
aList.Add("three")

For Each str As String in aList
    System.Console.WriteLine(str)
Next

Produces the following output:

one
two
three

Another option, would be to loop through using the index of each element:

Dim aList as New List(Of String)
aList.Add("one")
aList.Add("two")
aList.Add("three")

For i = 0 to aList.Count - 1 'We use "- 1" because a list uses 0 based indexing.
    System.Console.WriteLine(aList(i))
Next

Remove items from a List

Dim aList As New List(Of String)
aList.Add("Hello")
aList.Add("Delete Me!")
aList.Add("World")

'Remove the item from the list at index 1
aList.RemoveAt(1)

'Remove a range of items from a list, starting at index 0, for a count of 1)
'This will remove index 0, and 1!
aList.RemoveRange(0, 1)

'Clear the entire list
alist.Clear()

Retrieve items from a List

Dim aList as New List(Of String)
aList.Add("Hello, World")
aList.Add("Test")

Dim output As String = aList(0)

output:

Hello, World

If you do not know the index of the item or only know part of the string then use the Find or FindAll method

Dim aList as New List(Of String)
aList.Add("Hello, World")
aList.Add("Test")

Dim output As String = aList.Find(Function(x) x.StartWith("Hello"))

output:

Hello, World

The FindAll method returns a new List (of String)

Dim aList as New List(Of String)
aList.Add("Hello, Test")
aList.Add("Hello, World")
aList.Add("Test")

Dim output As String = aList.FindAll(Function(x) x.Contains("Test"))

output(0) = "Hello, Test"

output(1) = "Test"