How to take what was returned from a Task

Question

I have following code:

                List<UserItem> items = null;
                Task taskCreateItems = new Task(() => items = DeliverItems(Session, Item.GetBaseItem(i), (priceAmount * ((Item.Items.Count > 1) ? Item.Items[i] : Item.Amount)), ExtraData, (Page.MinRank > 1), Item.songID));
                taskCreateItems.Start();

This is the old code:

var items = DeliverItems(Session, Item.GetBaseItem(i), (priceAmount * ((Item.Items.Count > 1) ? Item.Items[i] : Item.Amount)), ExtraData, (Page.MinRank > 1), Item.songID));

With old code I could get what was returned, eg items.Count, items[0], but in new code using Task I don’t know how to do this.

Answer 1

After the taskCreateItems.Start();

Place var str_recebida = await taskCreateItems;

Don’t forget to put the function as Async for example:

private async void btn_Send_Click(object sender, EventArgs e){}

Answer 2

If you are trying to make this instruction work without interrupting the running code operation, I recommend using a TaskFactory.

Observing: if it is a STA/Windows Forms application, put this line in the application loading method:

Control.CheckForIllegalCrossThread = false;
// isso irá desativar as verificações de acesso aos membros feitos
// por threads em que os invocadores não fazem parte do Thread atual.

After that, do it in your code:

// declare a variável onde será utilizada pelo thread
List<UserItem> items = null;

// isso mesmo. Declare esse void dentro do void que você está
// trabalhando. isso será um sub-void.
void editarItems () {
     items = DeliverItems(Session, Item.GetBaseItem(i), (priceAmount * ((Item.Items.Count > 1) ? Item.Items[i] : Item.Amount)), ExtraData, (Page.MinRank > 1), Item.songID));
}

// inicie o thread
new System.Threading.Tasks.TaskFactory().StartNew(editarItems);

See working on .Net Fiddle, together with an excerpt indicating whether the method has been executed or not.

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Important: the declaration of sub-voids only works if you are using the compiler of C# Roslyn 2.0 or higher, which is installed by default in Visual Studio 2017 and 2019.