CODEWITHSUNDEEP
c#c#-4.0async-await
Ramesh
Ramesh

Reputation: 253

Since this is an async method, the return expression must be of type 'Data' rather than 'Task<Data>'

 public async Task<Data> GetData()
    {
        Task<Data> data = null;

        //This data will be fetched from DB
        Data obj = new Data();
        obj.ID = 1;
        obj.Name = "Test";

        //Need to 
        // data = obj;

        return Task.Run(() =>
        {
            return obj;
        });

    }

Error 1 Since this is an async method, the return expression must be of type 'WebApplication2.Data' rather than 'Task' \inb-fs01\Users\user\Visual Studio 2012\Projects\WebApplication2\WebApplication2\Home.aspx.cs 35 20 WebApplication2

Can someone help me sorting out this issue?

Upvotes: 16

Views: 14414

Answers (6)

Muhammad Aftab
Muhammad Aftab

Reputation: 1118

Try this:

return Task.FromResult(obj);

Upvotes: 0

iman nasser
iman nasser

Reputation: 71

if you write asp.net core

return await GetData();

Upvotes: 4

Awn Ali
Awn Ali

Reputation: 1379

Where ever u are calling this function, try to put await before that call, like below:

Data obj = await GetData();

And return Data object simply from GetData() method.

Upvotes: 2

Panagiotis Kanavos
Panagiotis Kanavos

Reputation: 131219

I'll agree with the other answers - this example is too artificial to give a good answer. There is really no reason to put async on a method that just wants to return an object.

async\await by themselves don't make a method run asynchronously, it's only syntactic sugar that allows awaiting for already asynchronous operations to complete.

Just for completeness, the following options should be considered as well:

  • Return a Task object without using async/await at all. If the method doesn't have anything to do after Task.Run, there is no reason to await.

    public Task<Data> GetData()
{
    ....
    return Task.Run(() =>
    {
        //Do something time consuming
        return obj;
    });
}

  • Don't use Task.Run if all that's needed is to return a piece of data. Use Task.FromResult to return a pre-computed task. This assumes that the callers of the method really need it to return a Task, otherwise this example should be converted to a plain method

    public Task<Data> GetData()
{
    ....
    return Task.FromResult(obj);
}

Upvotes: 5

NeddySpaghetti
NeddySpaghetti

Reputation: 13495

Change your code to await Task.Run. I.e.

    return await Task.Run(() =>
    {
        return obj;
    });

The compiler generates a state machine for async methods so for a method returning Task<T>, you actually return T and the compiler wraps it in a Task in the generated state machine.

I assume this is some sort of exercise or a simplified example as the method does not need to be async at all.

Upvotes: 18

dcastro
dcastro

Reputation: 68640

Well, "since this is an async method, the return expression must be of type Data rather than Task<Data>".

So, change this:

return Task.Run(() =>
    {
        return obj;
    });

to this:

return obj;

Also, why are you making this method async in the first place?

Upvotes: 5

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