Adding Objects to the ArrayList
Adding objects is simple just use the add method:
Dim al As New ArrayList()
al.Add("This")
al.Add("Is")
al.Add("My")
al.Add("New")
al.Add("ArrayList")
al.Add("Control")
This adds 6 new objects to the arraylist.
Reading the Values of the ArrayList
To read the values you can iterate though each of the items in the Item collection like so:
Dim i As Integer
For i = 0 To al.Count - 1
Console.WriteLine(CStr(al.Item(i)))
Next
If you prefer you can use an Enumerator like this:
Dim en As IEnumerator = al.GetEnumerator
While en.MoveNext
Console.WriteLine(en.Current)
End While
Searching The ArrayList
To search for the existence of an object in the ArrayList, you can use the BinarySearch method:
Dim al As New ArrayList()
al.Add("This")
al.Add("Is")
al.Add("My")
al.Add("New")
al.Add("ArrayList")
al.Add("Control")
'Do a case Insensitive search
Dim idx As Integer = al.BinarySearch("my", New CaseInsensitiveComparer())
If idx > 0 Then
MessageBox.Show("Found at Index " & idx)
Else
MessageBox.Show("Not Found")
End If
Note that we use a CaseInsensitiveComparer object above, you could also do this:
Dim idx As Integer = al.BinarySearch("my")
If you do not specify the IComparer implementation the default is a case sensitive compare. So the line above will return the "Not Found" message.
Sorting the ArrayList Ascending
There are a few different options to sorting but the basic is a simple Ascending Case Sensitive Sort:
This code assumes there is a button on your form called Button1
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles Button1.Click
Dim al As New ArrayList()
al.Add("This")
al.Add("Is")
al.Add("My")
al.Add("New")
al.Add("ArrayList")
al.Add("Control")
Console.WriteLine("Before Sort:")
WriteElements(al)
al.Sort()
Console.WriteLine("After Sort:")
WriteElements(al)
End Sub
Private Sub WriteElements(ByVal al As ArrayList)
Dim i As Integer
For i = 0 To al.Count - 1
Console.WriteLine(CStr(al.Item(i)))
Next
End Sub
Here is what the output will look like in the console window:
Before Sort:
This
Is
My
New
ArrayList
Control
After Sort:
ArrayList
Control
Is
My
New
This
The sort command physically reorders each object, so you can even use the Enumerator to list each of the values and you will get the same value, shown in the next example below.
Descending ArrayList Sort
This can be done by adding one line to the code above:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim al As New ArrayList()
al.Add("This")
al.Add("Is")
al.Add("My")
al.Add("New")
al.Add("ArrayList")
al.Add("Control")
Console.WriteLine("Before Sort:")
WriteElements(al)
al.Sort()
al.Reverse()
Console.WriteLine("After Sort:")
WriteElements(al)
End Sub
Private Sub WriteElements(ByVal al As ArrayList)
Dim en As IEnumerator = al.GetEnumerator
While en.MoveNext
Console.WriteLine(en.Current)
End While
End Sub
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