如何在.net 4.0中正确使用async/await
本文关键字:async await net | 更新日期: 2023-09-27 18:17:52
由于某些原因,我需要回到。net版本,所以我是4.5,现在是4.0,我有冲突与我的异步方法:我有WCF服务,我想执行异步方法并等待它们,所以在4.5中我这样做了:wcf:
public async Task<DataTable> ProcessSomething(string Param1, int Param2)
{
return await Task.Run(() =>
{
return new DataTable("aaa");
});
}
和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..
}
}
但是当我恢复到4.0时,服务和客户端都必须使用nuget库:
https://www.nuget.org/packages/Microsoft.Bcl.Async/
现在在WCF 4.0中,我有这个:
public async Task<DataTable> ProcessSomething(string Param1, int Param2)
{
return await Task.Factory.StartNew(() =>
{
return new DataTable("aaa");
});
}
和在客户端我尝试这个:
DataTable ProcessSomethingResult = await Client.Instance.____Client.ProcessSomethingAsync(Param1, Param2);
但是弹出错误提示:cannot await void…如果我调用:
DataTable ProcessSomethingResult = Client.Instance.____Client.ProcessSomething(Param1, Param2);
它返回数据表没有问题…但是async返回void ..为什么?如何解决这个问题呢?TNX提前…
//在评论中你问我进程某事的定义,这里是:
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);
}
});
}
在旧版本的WCF中,异步函数与Begin/End语句绑定。使用基于任务的异步代理可能会导致您遇到的问题。
重新生成您的客户端代理,以便您拥有Begin/End组合并使用TaskFactory.FromAsync
将其转换为可以使用Microsoft.Bcl.Async
等待的任务。
//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);
}
}