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I have multiple tasks returning the same object type that I want to call using Task.WhenAll(new[]{t1,t2,t3}); and read the results.
When I try using
Task<List<string>> all = await Task.WhenAll(new Task[] { t, t2 }).ConfigureAwait(false);
I get a compiler error
Cannot implicitly convert type 'void' to
'System.Threading.Tasks.Task<System.Collections.Generic.List<string>>
both tasks are calling method similar the this.
private Task<List<string>> GetFiles(string path)
{
files = new List<string>();
return Task.Run(() =>
{
//remove for brevity
return files;
});
}
556
public static Task WhenAll (params Task[] tasks); Task. WhenAll creates a task that will complete when all of the supplied tasks have been completed. It's pretty straightforward what this method does, it simply receives a list of Tasks and returns a Task when all of the received Tasks completes.
WhenAll(Task[])Creates a task that will complete when all of the Task objects in an array have completed.
The recommended return type of an asynchronous method in C# is Task. You should return Task<T> if you would like to write an asynchronous method that returns a value. If you would like to write an event handler, you can return void instead. Until C# 7.0 an asynchronous method could return Task, Task<T>, or void.
The Task. WaitAll blocks the current thread until all other tasks have completed execution. The Task. WhenAll method is used to create a task that will complete if and only if all the other tasks have completed.
Looks like you are using the overload of WaitAll() that doesn't return a value. If you make the following changes, it should work.
List<string>[] all = await Task.WhenAll(new Task<List<string>>[] { t, t2 })
.ConfigureAwait(false);
The return type of WhenAll is a task whose result type is an array of the individual tasks' result type, in your case Task<List<string>[]>
When used in an await expression, the task will be "unwrapped" into its result type, meaning that the type of your "all" variable should be List<string>[]
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