Explain me await magic and give .NET 4.0 alternative for it.

Question

I am working with .NET 4.0 and I can't use Microsoft Async/Await features. But I want to add this analog in my application for TASK.

Correct me if I am mistaken.

var task = Task.Factory.StartNew<string>(() => GetURLContents(0))
.ContinueWith(t => this.textBox1.Text = t.Result, TaskScheduler.FromCurrentSynchronizationContext());

MessageBox.Show("Finished");

In this code current thread will be executed further. And Message Finished will be raised before task will be finished.

Of course you can say - use ContinueWith. But I want that this code will be executed in the same thread and after operation is finihed. And I don't want current thread code will be executed further.

You can say - Use task.Wait.

var task = Task.Factory.StartNew<string>(() => GetURLContents(0))
.ContinueWith(t => this.textBox1.Text = t.Result, TaskScheduler.FromCurrentSynchronizationContext());

task.Wait();
MessageBox.Show("Finished");

But task.Wait is blocking current thread. And if I show progress bar while GetURLContents executed UI will be frozen.

But lets look at await

this.textBox1.Text = await GetURLContentsAsync(0)
MessageBox.Show("Finished");

As I can understand with Await:

1. Current thread is Not executed further until "Task" is not finished
2. Current thread is Not blocked ( UI is not frozen ) while we waiting result

Q1 :But how can it be ? I read somewhere that it works closely like yeld work and this especial compiler trick. And as I can understand I can't find alternative for it at all.

Q2 :How I can realise such functioanlity in .NET 4.0 ? ( May be I can add some async CTP dll to my project )

Q3: Should I explore ReactiveCommand from Reactive UI and Reactive Extension or with await/async there will be no necessary of them. And await/async will kill them because it will solve the same thing more simplier ?

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I create my super player Media Glass

Answer 1

I find it hard to understand what you're saying. But you can use async-await with .Net 4.0, if you use Visual Studio 11 with the Async Targetting Pack.