Более серьезный пример: извлечение данных из кода HTML
Ниже приведен полный текст программы:
Option Strict On Imports System.IO Imports System.Net
Imports System.Threading
Module Modulel
Sub Main()
Dim theBook(3.1) As String
theBook(0.0) = "1893115992"
theBook(0.l) = "Programming VB.NET"
theBook(l.0) = "1893115291"
theBook(l.l) = "Database Programming VB.NET"
theBook(2.0) = "1893115623"
theBook(2.1) = "Programmer 's Introduction to C#."
theBook(3.0) = "1893115593"
theBook(3.1) = "Gland the .Net Platform "
Dim i As Integer
Dim theRanker As =AmazonRanker
Dim aThreadStart As Threading.ThreadStart
Dim aThread As Threading.Thread
For i = 0 To 3
Try
theRanker = New AmazonRankerttheBook(i.0) .theBook(i.1))
aThreadStart = New ThreadStart(AddressOf theRanker. FindRank)
aThread = New Thread(aThreadStart)
aThread.Name= theBook(i.l)
aThread.Start()
Catch e As Exception
Console.WriteLlnete.Message)
End Try Next
Console.ReadLine()
End Sub
End Module
Public Class AmazonRanker
Private m_URL As String
Private m_Rank As Integer
Private m_Name As String
Public Sub New(ByVal ISBN As String. ByVal theName As String)
m_URL = "http://www.amazon.com/exec/obidos/ASIN/" & ISBN
m_Name = theName End Sub
Public Sub FindRank() m_Rank = ScrapeAmazon()
Console.Writeline("the rank of " & m_Name & "is "
& GetRank) End Sub
Public Readonly Property GetRank() As String Get
If m_Rank < > 0 Then
Return CStr(m_Rank) Else
' Проблемы
End If
End Get
End Property
Public Readonly Property GetName() As String Get
Return m_Name
End Get
End Property
Private Function ScrapeAmazon() As Integer Try
Dim theURL As New Uri(m_URL)
Dim theRequest As WebRequest
theRequest =WebRequest.Create(theURL)
Dim theResponse As WebResponse
theResponse = theRequest.GetResponse
Dim aReader As New StreamReader(theResponse.GetResponseStream())
Dim theData As String
theData = aReader.ReadToEnd
Return Analyze(theData)
Catch E As Exception
Console.WriteLine(E.Message)
Console.WriteLine(E.StackTrace)
Console. ReadLine()
End Try End Function
Private Function Analyze(ByVal theData As String) As Integer
Dim Location As.Integer Location = theData.IndexOf("<b>Amazon.com
Sales Rank:</b>") _
+ "<b>Amazon.com Sales Rank:</b>".Length
Dim temp As String
Do Until theData.Substring(Location.l) = "<" temp = temp
&theData.Substring(Location.l) Location += 1 Loop
Return Clnt(temp)
End Function
End Class
Примечание
Многопоточные операции часто используются в .NET и пространствах имен ввода-вывода, поэтому в библиотеке .NET Framework для них предусмотрены специальные асинхронные методы. Дополнительная информация о применении асинхронных методов при написании многопоточных программ приведена в описании методов BeginGetResponse и EndGetResponse класса HTTPWebRequest.