Why should I use Result in Tasks C#?

Question

I've seen that when you use Task Class like this:

 Task<Test> task2 = Task<Test>.Factory.StartNew(() =>
            {
                string s = ".NET";
                double d = 4.0;
                for (int i = 0; i < 3; i++) { }
                return new Test { Name = s, Number = d };
            });

You can use Test tt = task2.Result; to get a result back from a Task . However, the thread does not run in background, my whole program waits for it to stop and send the data back, so why should I even use this? I can simply use a function.

So, for me to get a result back I need to run another task that will run this task? (or another thread, doesn't matter).

Is there any way to not wait and still get result?

Answer 1

Any way to not wait and still get result?

No, because there isn't a result until the task has completed.

The point is that you can maintain a reference to the task, perform some other operations, and then get the result.

Note that C# 5 makes it a lot easier to chain asynchronous operations together using async and await - that way when operation X needs to wait for operation Y to complete, it can await it, and the caller of operation X gets a task representing that ongoing operation... when Y has completed, X will resume, and when that completes, the task returns to the caller will also complete.

Answer 2

Any way to not wait and still get result?

Yes, you would use a continuation. This can be scheduled to run on the current synchronization context (so if you're in a UI application, the UI thread), as well.

This would look like:

Task<Test> task2 = Task.Factory.StartNew(() =>
{
    string s = ".NET";
    double d = 4.0;
    for (int i = 0; i < 3; i++) { }
    return new Test { Name = s, Number = d };
});

task2.ContinueWith(t =>
{
    // This runs when things are done
    Test tt = t.Result;
    // use tt
}, TaskScheduler.FromCurrentSynchronizationContext());

If you are using C# 5 and .NET 4.5, this becomes far simpler:

Test tt = await Task.Run(() =>
{
    string s = ".NET";
    double d = 4.0;
    for (int i = 0; i < 3; i++) { }
    return new Test { Name = s, Number = d };
});

// use tt