Asynchronous programming in a portable library
I am very confused about the new async stuff. I have a portable library implementing my model with some classes with virtual functions that I hope to use in ASP.NET, WPF, Windows Store, Silverlight 5, and Windows Phone 8. They can target WCF functionality, CSharp SQLite, or be overridden by platform-specific libraries for a local file.
How do I set it up now that synchronous programming is frowned upon in the Windows Store world? I tried adding async keywords, etc. Into a portable library for virtual functions, but it says that I don't have the required frameworks. How can I reuse this library without rewriting it? Is OOP programming completely dead now?
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VS will happily allow async
in portable libraries targeting .NET 4.5 and Windows Store. If you need other platforms (especially .NET 4.0 and Silverlight 5), you need to install Microsoft.Bcl.Async .
If you need a link, the source is available for my AsyncEx library ; the main assembly is a portable library that depends on Microsoft.Bcl.Async.
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The way I refer to it is to use a helper class that I adapted from a previous version. Basically:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Windows.UI.Core;
using Windows.UI.Xaml;
namespace JTModelsWinStore.Local
{
public delegate void UseDataDelegate(DataCoordinator data);
public delegate bool GetDataDelegate(DataCoordinator data);
public class DataCoordinator
{
public DependencyObject Consumer;
public GetDataDelegate GetDataFunction;
public UseDataDelegate UseDataFunction;
public bool GetDataSucceeded;
public Exception ErrorException;
public string ErrorMessage;
public DataCoordinator(
DependencyObject consumer,
GetDataDelegate getDataFunction,
UseDataDelegate useDataFunction)
{
Consumer = consumer;
GetDataFunction = getDataFunction;
UseDataFunction = useDataFunction;
GetDataSucceeded = false;
ErrorException = null;
ErrorMessage = null;
}
public Task GetDataAsync()
{
GetDataSucceeded = false;
Task task = Task.Factory.StartNew(() =>
{
if (GetDataFunction != null)
{
try
{
GetDataSucceeded = GetDataFunction(this);
}
catch (Exception exception)
{
GetDataSucceeded = false;
ErrorException = exception;
ErrorMessage = exception.Message;
}
}
if (UseDataFunction != null)
{
if (Consumer != null)
{
var ignored = Consumer.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
UseDataFunction(this);
});
}
else
UseDataFunction(this);
}
});
return task;
}
}
}
and then in your windows store code:
private async void ItemView_ItemClick(object sender, ItemClickEventArgs e)
{
DataCoordinator data = new DataCoordinator(this, Logon, LogonCompleted);
await data.GetDataAsync();
}
private bool Logon(DataCoordinator data)
{
LoggedOnUserID = ServiceClient.LogOn(UserName, Password);
if (LoggedOnUserID == null)
{
UserName = "AnonymousUser";
Password = "";
if (!String.IsNullOrEmpty(ServiceClient.ErrorMessage))
data.ErrorMessage = "Log on failed.";
return false;
}
if (!String.IsNullOrEmpty(ServiceClient.ErrorMessage))
{
data.ErrorMessage = ServiceClient.ErrorMessage;
return false;
}
return true;
}
private void LogonCompleted(DataCoordinator data)
{
if (data.GetDataSucceeded && LoggedOnUserID != null)
pageTitle.Text = "Logged On";
else
pageTitle.Text = "LogOn Failed";
}
I provide the helper with two functions, one for getting data (slow) and one for doing something with the data in the UI. I know I can do this in two nested lambdas, but I like to hide two lambdas, which is more convenient for an old timer like me.
Please feel free to criticize it, both for others and for my own.
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