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c#wcfasynchronous.net-4.0async-await
ShadyOverflow
ShadyOverflow

Reputation: 105

How to properly use async/await in .NET 4.0

for some reasons i needed to go back version of .net, so i was 4.5 and now im 4.0, and im having conflict with my async methods: i have wcf service, and i want to execute the async methods and await them, so in 4.5 i did this: wcf:

public async Task<DataTable> ProcessSomething(string Param1, int Param2)
        {
            return await Task.Run(() =>
            { 
            return new DataTable("aaa");
            });
        }

and 4.5 client:

private static async Task<bool> ProcessSomethingAsync(string Param1, int Param2)
        {
            decimal payin = 0;
            Task<DataTable> result = Client.Instance.___Client.ProcessSomethingAsync(Param1, Param2);
            if (result == await Task.WhenAny(result, Task.Delay(1000)))
            {
                //code here..
            }
        }

but when i reverted to 4.0, both, the service and the client, i had to use nuget library:

https://www.nuget.org/packages/Microsoft.Bcl.Async/

now in wcf 4.0 i have this:

public async Task<DataTable> ProcessSomething(string Param1, int Param2)
        {
            return await Task.Factory.StartNew(() => 
            {
                return new DataTable("aaa");
            });
        }

and in client i try this:

DataTable ProcessSomethingResult = await Client.Instance.____Client.ProcessSomethingAsync(Param1, Param2);

but error pops up saying: cannot await void... if i call:

DataTable ProcessSomethingResult = Client.Instance.____Client.ProcessSomething(Param1, Param2);

it returns datatable no problem ... but async is returning void .. why ? and how to solve this ... tnx in advance..

//in comments you asked me for the definition of process something, here it is:

public async Task<DataTable> ProcessTicket(string Barcode, int ClientID)
        {
            return await Task.Factory.StartNew(() => 
            {
                try
                {
                    DataTable dt = new DataTable("ProcessTicket");
                    using (SqlConnection con = new SqlConnection(TempClass._DatabaseConnectionString))
                    {
                        using (SqlCommand com = new SqlCommand("SELECT * FROM dbo.ProcessTicket(@Barcode, @ClientID)", con))
                        {
                            con.Open();
                            com.CommandType = CommandType.Text;
                            com.Parameters.AddWithValue("@Barcode", Barcode);
                            com.Parameters.AddWithValue("@ClientID", ClientID);
                            dt.Load(com.ExecuteReader());
                            if (dt == null)
                                throw new FaultException("DataTable from database is null.");
                            return dt;
                        }
                    }
                }
                catch (Exception ex)
                {
                    Logs.Instance.AppendLogs(ex.Message, MethodBase.GetCurrentMethod().Name);
                    throw new FaultException(ex.Message);
                }
            });
        }

Upvotes: 2

Views: 6117

Answers (1)

Scott Chamberlain
Scott Chamberlain

Reputation: 127543

In the older versions of WCF the async functions where tied to Begin/End statements. Using the task based async proxes will likely cause problems like you are running in to.

Regenerate your client proxies so you have the Begin/End combos and use TaskFactory.FromAsync to convert it in to a task which can be awaited on using Microsoft.Bcl.Async.

//put this in a seperate file, client proxies are usually marked "partial" so you can 
// add functions on like this and not have them erased when you regenerate.
partial class YourClientProxy
{
    public Task<DataTable> ProcessSomethingAsync(string Param1, int Param2)
    {
        return Task<DataTable>.Factory.FromAsync(this.BeginProcessSomething, this.EndProcessSomething, Param1, Param2, null);
    }
}

Upvotes: 2

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