Call async method in constructor?

Question

I used to call async methods (fire and forgot?) in constructors by

 Task.Run(async () => await CallAsync());

I heard it's better to use ICommand to execute it.

ICommand MyCmd => new Command(async () => await CallAsync());

public MyClass()
{
     MyCmd.Execute(null);
}

What's the difference between these two methods?

You shouldnt perform any processing in constructors in the first place — FCin, Nov 21 '18 at 05:31
`HostingEnvironment.QueueBackgroundWorkItem` is recommended mostly, take a look at here https://blog.stephencleary.com/2014/06/fire-and-forget-on-asp-net.html — Just code, Nov 21 '18 at 05:34
@FCin, it says initializing the WinForms controls in the constructor can be much faster in this question, https://stackoverflow.com/questions/2521322/what-setup-code-should-go-in-form-constructors-versus-form-load-event. — ca9163d9, Nov 21 '18 at 06:11
This refers to updating controls. I'm talking about processing/retrieving data which I assume you do, because you clearly await something. Also, you haven't tagged your question with what framework you are using. WinForms I assume? — FCin, Nov 21 '18 at 06:21
@FCin, the async method calls methods which read database asynchronously and initialize the controls with the data. — ca9163d9, Nov 21 '18 at 06:25
You've mentioned WinForms and WPF... Could you please clarify what framework you are targeting? Without it looks like dup of https://stackoverflow.com/questions/21354550/async-method-which-is-called-from-constructor (or similar posts) — Alexei Levenkov, Nov 21 '18 at 06:39
You're violating the expectation that when a constructor returns, the object is correctly initialized and ready to be used. Consider instead using a *factory* that performs the async works and passes the *results* of that work into an appropriately parameterized constructor for this class instead. That factory method can be `async`. — Damien_The_Unbeliever, Nov 21 '18 at 07:08
For initializing forms and retrieving data a constructor is the wrong place. you should react on an event being fired — Daniel Schmid, Sep 18 '19 at 12:26

score 9 · Answer 1 · answered Sep 18 '19 at 12:26

Your post makes not much sense.

If you want to fire-and-forget an async method, then just calling it directly is enough.

public Task RunAsync() { }

public Constructor()
{
    RunAsync(); // fire-and-forget by not awaiting and ignoring returned task
}

There is no need to use Task.Run or Command, which technically does nothing on top of running the method.

But this kind of fire-and-forget code is frowned upon, because it makes testing of the code difficult. And starting such code in constructor makes the object creation have unexpected side-effects that are not immediately obvious. It is recommended to have some kind of Initialize method that can be called.

Another issue is that if the method causes an exception, a special handler must be register, otherwise it crashes whole application.

Call async method in constructor?

1 Answers1