简单的 ASP.NET 4.5 异步和等待 VB.NET
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Simple ASP.NET 4.5 async and await in VB.NET
提问by sqlchris
I am trying to get a simple example of async with await working but I don't think it is. I am thinking this code should take 10 seconds (or just over 10 seconds) to run as each function within the for each loop is supposed to run asynchronously.
我正在尝试使用 await 来获取一个简单的异步示例，但我认为不是。我认为这段代码应该需要 10 秒（或刚刚超过 10 秒）来运行，因为 for each 循环中的每个函数都应该异步运行。
This is an asp.net web forms and Async="true" is present in the page declaration.
这是一个 asp.net 网络表单，页面声明中存在 Async="true"。
Inherits System.Web.UI.Page
Protected Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
'This needs to execute different asynchronous processes based on the array value
Dim ItemList(2) As String
ItemList(0) = "A"
ItemList(1) = "B"
ItemList(2) = "C"
Dim time_start As DateTime
Dim time_end As DateTime
Dim r1 As String
Dim r2 As String
Dim r3 As String
'capture start time
time_start = DateTime.Now
'run async processes for each item in array
For Each element As String In ItemList
Select Case element
Case "A"
r1 = Await processAsyncA(10) & " "
Case "B"
r2 = Await processAsyncB(10) & " "
Case "C"
r3 = Await processAsyncC(10) & " "
End Select
Next
'capture end time
time_end = DateTime.Now
'display total duration in seconds
Label1.Text = DateDiff(DateInterval.Second, time_start, time_end)
End Sub
Protected Async Function processAsyncA(ByVal waittime As Integer) As Task(Of String)
Await Task.Delay(waittime * 1000)
Return waittime.ToString
End Function
Protected Async Function processAsyncB(ByVal waittime As Integer) As Task(Of String)
Await Task.Delay(waittime * 1000)
Return waittime.ToString
End Function
Protected Async Function processAsyncC(ByVal waittime As Integer) As Task(Of String)
Await Task.Delay(waittime * 1000)
Return waittime.ToString
End Function
Thanks in advance!
提前致谢！
回答by Damien_The_Unbeliever
No, they won't run asynchronously because you've said "don't carry on until you've got the result" here:
不，它们不会异步运行，因为您在这里说过“在得到结果之前不要继续”：
r1 = Await processAsyncA(10)
What you should instead do is launch all of the processXXXfunctions and thenawait all of them. Something like:
您应该做的是启动所有processXXX功能，然后等待所有功能。就像是：
Dim l as New List(Of Task(Of String))
'run async processes for each item in array
For Each element As String In ItemList
Select Case element
Case "A"
l.Add(processAsyncA(10))
Case "B"
l.Add(processAsyncB(10))
Case "C"
l.Add(processAsyncC(10))
End Select
Next
r1 = Await l(0) & " "
r2 = Await l(1) & " "
r3 = Await l(2) & " "
(Not the cleanest code, but hopefully you get the gist)
（不是最干净的代码，但希望你能明白要点）
