CODEWITHSUNDEEP
vb.netasynchronous
spinjector
spinjector

Reputation: 3515

In VB.Net, how can I create a method that waits for a variable number of asynchronous calls to complete, and then returns a result?

How can I code a method in VB.Net 2012 that waits for a variable number of asynchronous calls to complete, and only when all calls finish will then return a result?

I'm writing an app that retrieves a value from various web pages, and then returns the sum of those values. The number of values to retrieve will be determined by the user at runtime. As web retrieval is asynchronous by nature, I'm trying to make the app more efficient by coding it as such. I've just read about the keywords Async and Await, which seem perfect for the job. I also found this example of how to do it in C#: Run two async tasks in parallel and collect results in .NET 4.5.

But there are two issues with this example: 1) At first glance, I don't know how to make the same thing happen in VB.Net, and 2) I don't know how it could be redesigned to handle a variable number of called tasks.

Here's a pseudo-translation from the example, of what I hope to achieve:

Function GetSumOfValues(n as Integer)
   For i = 1 To n
      GetValueAsync<i>.Start()
   Next i
   Dim result = Await Task.WhenAll(GetValueAsync<?*>)
   Return result.Sum()
End Function

Note the question mark, as I'm not sure if it's possible to give WhenAll a "wildcarded" group of tasks. Perhaps with an object collection?

Upvotes: 1

Views: 240

Answers (1)

T.S.
T.S.

Reputation: 19340

You can use this example of using tasks with Task.WaitAll

Now, to collect data asynchronously, you can use a static method with sync lock. Or one of the synchronized collections

Upvotes: 1

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