wwwdummiescom/go/aspnetaiofd in .NET

Creation UPC-A Supplement 2 in .NET wwwdummiescom/go/aspnetaiofd

Listing 3-1: DemoEnumeratoraspxvb (VB)

Partial Class DemoEnumerator Inherits SystemWebUIPage Protected Sub Page_Load(ByVal sender As Object, _ ByVal e As SystemEventArgs) _ Handles MeLoad Dim al As New ArrayList alAdd(10) alAdd(15) alAdd( hello ) alAdd(20) alAdd( goodbye ) Iterate using a for loop

Dim index As Int32 For index = 0 To alCount - 1 ResponseWrite(al(index)) ResponseWrite( <br> ) Next ResponseWrite( <br> ) Iterate using a for-each loop Dim obj As Object For Each obj In al ResponseWrite(objToString) ResponseWrite( <br> ) Next ResponseWrite( <br> ) Iterate using the IEnumerator interface Dim en As IEnumerator en = alGetEnumerator While enMoveNext obj = enCurrent ResponseWrite(objToString) ResponseWrite( <br> ) End While End Sub End Class

Listing 3-2: DemoEnumeratorCSaspx (C#)

using System; using SystemCollections; public partial class DemoEnumerator2 : SystemWebUIPage { protected void Page_Load(object sender, EventArgs e) { ArrayList al = new ArrayList(); alAdd(10); alAdd(15); alAdd( hello ); alAdd(20); alAdd( goodbye ); // Iterate using a for loop Int32 index; for (index = 0; index <= alCount - 1; index++) { ResponseWrite(al[index]); ResponseWrite( <br> ); } ResponseWrite( <br> ); // Iterate using a for-each loop foreach (Object obj in al) { ResponseWrite(objToString());

(continued)

Listing 3-2: (continued)

ResponseWrite( <br> ); } ResponseWrite( <br> ); // Iterate using the IEnumerator interface IEnumerator en; en = alGetEnumerator(); Object o; while (enMoveNext()) { o = enCurrent; ResponseWrite(oToString()); ResponseWrite( <br> ); } } }

The Page_Load method in both listings 3-1 and 3-2 creates a new ArrayList instance and adds several items to the instance Next, the code demonstrates how to iterate through the ArrayList collection using a For loop You can see how I created an Int32 variable that serves as the index for the loop Next is the loop itself The loop goes from 0 to one less than the number of items in the collection (Arrays and collections in NET start with 0 as the index thus the maximum number is one less than the total number of items in the collection) With each iteration of the loop, I write out the item in the loop To access the item, I use a syntax similar to that of arrays Here s the VBNET version:

ResponseWrite(al(index))

The individual item is specified with (al(index)) For C#, you use square brackets instead of parentheses:

ResponseWrite(al[index]);

In both the VB and C# versions, I then write out a <br> tag to start a new line in the Web browser After finishing the first loop, I begin iterating through the collection, using the For Each construct In the VBNET version (Listing 3-1), the first thing I do is declare an Object instance that gets the value of each item in the collection through each step of the iteration In the C# version (Listing 3-2), you can t declare the iterator variable used by foreach prior to the foreach statement Instead, you declare the iterator variable right inside the foreach statement, like so:

foreach (Object obj in al)

Notice also that if you re using VBNET, you use two separate, initial-capped words: For Each If you re using C#, you use a single, lowercased word without a space, foreach In VBNET, the For Each construct is incredibly easy to use: After you set up the iteration with the For Each call, the elements of the collection simply get stored in the variable specified in the For Each statement

The ArrayList class is an incredibly useful class that simply stores things; it s a no-frills storage class However, it s more useful than just a regular old array because you can store anything you want in it It provides methods for adding to the container, and other methods such as those for accessing the items Take a look at the following VB code; it demonstrates a basic usage of the ArrayList class

Class SomeClass Dim X As Int32 Dim Y As Int32 Public Sub New(ByVal AX As Int32, ByVal AY As Int32) X = AX Y = AY End Sub Public Overrides Function ToString() As String Return StringFormat( ({0},{1}) , X, Y) End Function End Class Sub ArrayListDemo() Dim al As New ArrayList alAdd(1) alAdd( Hello ) alAdd(New SomeClass(10, 20)) Dim obj As Object For Each obj In al ResponseWrite(objToString) ResponseWrite( <br> ) Next ResponseWrite( <br><br> ) Dim index As Integer For index = 0 To alCount - 1 obj = al(index) ResponseWrite(objToString) ResponseWrite( <br> ) Next End Sub