Getting web page after calling DownloadStringAsync()?
- by OverTheRainbow
Hello
I don't know enough about VB.Net yet to use the richer HttpWebRequest class, so I figured I'd use the simpler WebClient class to download web pages asynchronously (to avoid freezing the UI).
However, how can the asynchronous event handler actually return the web page to the calling routine?
Imports System.Net
Public Class Form1
Private Shared Sub DownloadStringCallback2(ByVal sender As Object, ByVal e As DownloadStringCompletedEventArgs)
If e.Cancelled = False AndAlso e.Error Is Nothing Then
Dim textString As String = CStr(e.Result)
'HERE : How to return textString to the calling routine?
End If
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim client As WebClient = New WebClient()
AddHandler client.DownloadStringCompleted, AddressOf DownloadStringCallback2
Dim uri As Uri = New Uri("http://www.google.com")
client.DownloadStringAsync(uri)
'HERE : how to get web page back from callback function?
End Sub
End Class
Thank you.
Edit: I added a global, shared variable and a While/DoEvents/EndWhile, but there's got to be a cleaner way to do this :-/
Public Class Form1
Shared page As String
Public Shared Sub AlertStringDownloaded(ByVal sender As Object, ByVal e As DownloadStringCompletedEventArgs)
' If the string request went as planned and wasn't cancelled:
If e.Cancelled = False AndAlso e.Error Is Nothing Then
page = CStr(e.Result)
End If
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim wc As New WebClient
AddHandler wc.DownloadStringCompleted, AddressOf AlertStringDownloaded
page = Nothing
wc.DownloadStringAsync(New Uri("http://www.google.com"))
'Better way to wait until page has been filled?
While page Is Nothing
Application.DoEvents()
End While
RichTextBox1.Text = page
End Sub
End Class
