Good day! I am trying to write an anonymous method using lambda expressions which would return an object from an async task. I would like to do this in the constructor, so that is the reason I can't make its parent method async.
The ReadJsonAsync method returns a Session object.
I will show you the relevant code:
Session session;
fileService = new FileService();
session = async () => { return await fileService.ReadJsonAsync() };
Thanks in advance!
If you want an Anonymous Method, you'll have to declare one which returns a Task<Session> as it is marked with the async modifier, hence must return a void (only for async event handlers), Task or Task<T> :
Func<Task<Session>> anonFunction = async () => await fileService.ReadJsonAsync();
If all you do is run ReadJsonAsync, you may also save yourself the state machine generation like so:
Func<Task<Session>> anonFunction = fileService.ReadJsonAsync;
Then you can await on it higher up the call stack:
Func<Task<Session>> anonFunction = fileService.ReadJsonAsync;
await anonFunction();
To add to Yuval's useful answer, if you just want to await an inline function, then the magic syntax is:
await ((Func<Task>)(async () =>
{
//async function code
}
))();
Note the extra brackets on the end to call the lambda immediately after declaration. Obviously if your function returns a type, then it would be Func<Task<Whatever>>
Useful if you're using Task.WhenAny() for example to await both an inline function and a timeout task.
Sessiona delegate type? What are you trying to do? - Yuval ItzchakovSessionobject, which makes no sense. You're trying to store a "method returning Session" into a "Session". You should be storing it into a delegate (which is how you store methods). - Raymond Chenreturn await fileService.ReadJsonAsync()is redundant; you can just returnfileService.ReadJsonAsync()directly and remove theasyncmodifier. - Thomas Levesque