Hopefully a fairly simple one here. I have a collection of objects, each of which has an async method that I want to call and collect values from. I'd like them to run in parallel. What I'd like to achieve can be summed up in one broken line of code:
IEnumerable<TestResult> results = await Task.WhenAll(myCollection.Select(v => v.TestAsync()));
I've tried various ways of writing this without success. Any thoughts?
If the tasks you're awaiting have a result of the same type Task.WhenAll returns an array of them. For example for this class:
public class Test
{
public async Task<TestResult> TestAsync()
{
await Task.Delay(1000); // Imagine an I/O operation.
return new TestResult();
}
}
We get these results:
var myCollection = new List<Test>();
myCollection.Add(new Test());
IEnumerable<TestResult> results = await Task.WhenAll(myCollection.Select(v => v.TestAsync()));
TestAsync accepts parameters, and is a static method ?
Do it like this:
public async Task RunMultipleTasksInParallelAsync()
{
var tasks = new List<Task<MyResultType>>(); //<---- Add the return type here
foreach (var item in items)
{
var task = DoSomethingAsync();
tasks.Add(task);
}
var myResults = await Task.WhenAll(tasks);
}
public async Task<MyResultType> DoSomethingAsync()
{
return new MyResultType();
}
Recogize that you have to add the return type into the task list, otherwhise Task.WhenAll will have the return type void.
TestAsynclook?TestAsync()signature was looking like this:public async TestResult TestAsync(), instead ofpublic async Task<TestResult> TestAsync().