ArrayList详细使用方法的实例

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