Writing awaitable methods

c# custom awaitable

Then we use the "ContinueWith" method to put in the code that we want to run when the task is complete. We can still get some benefit out of this library. You have to return void when you have async event handlers. NET thread is not blocked by the file download.

C# call awaitable method without await

In this case, you want to tell the awaiter to not capture the current context by calling ConfigureAwait and passing false, e. Just to show that we are not locking up our thread, I added the "for" loop to output the numbers 0 through 4 to our Console. The fact that it is 'for compiler use' is a poor excuse. NET request contexts are SynchronizationContext contexts. We can do that in our console application: Since "Get" returns a Task, we can directly check the "Result" property. We'll do the same action getting data from our repository and loading our list box , but we'll "await" things rather than deal with the Task directly. So, "await" will wait for the Task to finish and then give us the "Result" from the "Task". It looks like we have a bit of a problem. Later on, when the awaitable completes, it will execute the remainder of the async method. I've had some requests to dive into the topic, so we'll start with the basics and go deeper from there. For more details, see Stephen Toub's Should I expose asynchronous wrappers for synchronous methods?

When we call "Get", it returns immediately. As we'll see, "async" is important for what's inside the method, but what makes this particular method awaitable is that it returns a Task.

Now we only have 1 method instead of splitting into 2 methods even if one of those methods is a nested lambda expression.

async and await

The way the compiler tells the difference is whether the method is marked as "async". And even though this isn't all that difficult.

Change method to async c#

Complex answer: If SynchronizationContext. This is in the code-behind for the main window. NET request context. The problem is that since "await" was not a keyword before, it can't magically become one since it could break existing code that is using "await" as a variable name or something else like that. Await examines that awaitable to see if it has already completed; if the awaitable has already completed, then the method just continues running synchronously, just like a regular method. UI" project. The async keyword only enables the await keyword and manages the method results. Notice that once we add the "async" keyword to the method, the "await" operator is lit up and the squigglies are gone. I'm a little disappointed that await uses duck typing when an interface would be more appropriate for the language. The synchronization context is handled for us automatically. If we hover over the squigglies, it will tell us that we need the "async" keyword on the method. In this case, you want to tell the awaiter to not capture the current context by calling ConfigureAwait and passing false, e. Using "await" with an Awaitable Method Now we'll look at our second button. The primary use case for async void methods is event handlers.

Even though our method with "await" is easy for us to read and write, the compiler turns it into something a bit more complex. It looks more like our manual task with the continuation plus some other stuff. And we have to be careful if we return "void" because we lose visibility to any exceptions that might happen during the asynchronous operation.

UI and ASP.

Awaitable interface

We can write to the Console from whatever thread we like, so there is no need to get back to the main thread. So, let's run our application and try things out. With traditional threading, this is where we would use "Dispatcher. When we use "Result", we need to be aware that it could lock up our application. That is one option, but it's most likely not what you want to do, because it doesn't actually give you many of the advantages of asynchronous code. All it does is tell the compiler that if it finds "await" s in the method, it needs to treat them with the special context that we want here. Otherwise, it is treated just like any other identifier. Or we can use the "await" keyword and let the compiler generate that continuation for us. Even though our method with "await" is easy for us to read and write, the compiler turns it into something a bit more complex. But that also means we may need to wait a while before that promise is fulfilled. Before we look at creating our own asynchronous methods, we should look at how to consume asynchronous methods.

You can also use these methods along with Task. What is an "awaitable" method?

return await c#
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Writing tests for awaitable methods in Visual Basic