[WinHttp] [vb.net] Http 비동기 샘플 : 비동기 및 대기를 사용한 비동기 프로그래밍
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2020-05-25 08:51
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Imports System.Net.Http
' Example that demonstrates Asynchronous Progamming with Async and Await.
' It uses HttpClient.GetStringAsync to download the contents of a website.
' Sample Output:
' Working . . . . . . .
'
' Length of the downloaded string: 39678.
Class MainWindow
' Mark the event handler with Async so you can use Await in it.
Private Async Sub StartButton_Click(sender As Object, e As RoutedEventArgs)
' Call and await immediately.
' StartButton_Click suspends until AccessTheWebAsync is done.
Dim contentLength As Integer = Await AccessTheWebAsync()
ResultsTextBox.Text &= $"{vbCrLf}Length of the downloaded string: {contentLength}.{vbCrLf}"
End Sub
' Three things to note about writing an Async Function:
' - The function has an Async modifier.
' - Its return type is Task or Task(Of T). (See "Return Types" section.)
' - As a matter of convention, its name ends in "Async".
Async Function AccessTheWebAsync() As Task(Of Integer)
Using client As New HttpClient()
' Call and await separately.
' - AccessTheWebAsync can do other things while GetStringAsync is also running.
' - getStringTask stores the task we get from the call to GetStringAsync.
' - Task(Of String) means it is a task which returns a String when it is done.
Dim getStringTask As Task(Of String) =
client.GetStringAsync("https://docs.microsoft.com/dotnet")
' You can do other work here that doesn't rely on the string from GetStringAsync.
DoIndependentWork()
' The Await operator suspends AccessTheWebAsync.
' - AccessTheWebAsync does not continue until getStringTask is complete.
' - Meanwhile, control returns to the caller of AccessTheWebAsync.
' - Control resumes here when getStringTask is complete.
' - The Await operator then retrieves the String result from getStringTask.
Dim urlContents As String = Await getStringTask
' The Return statement specifies an Integer result.
' A method which awaits AccessTheWebAsync receives the Length value.
Return urlContents.Length
End Using
End Function
Sub DoIndependentWork()
ResultsTextBox.Text &= $"Working . . . . . . .{vbCrLf}"
End Sub
End Class
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