WinRT Consumer Preview: Calling C# (CSharp) Async class libraries from Javascript WinJS.Promises using then() clause

posted May 10, 2012

You probably already know that you can call C# Class Libraries from WinJS. Now that means I can define C# async methods and call it with WinJS.Promises right??

Think about it

This Javascript means the same as the C# counter part.

//C#
var csharpclass = new ClassLibrary1.Class1();
await csharpclass.testAsync();
// do something

//javascript
var csharpclass = new ClassLibrary1.Class1();
csharpclass.testAsync().then( function (e) {
    // do something ...
});

So does it mean I can avoid creating WinJS.Promises object for async method and use C# instead since it's (let's be honest) kinda confusing and do this instead?

// to avoid doubt: THIS DOES NOT WORK
// only wishful thinking!
public sealed class Class1
{
    public async void testAsync() 
    {
        // do this asynchronously ...
    }
}

wouldn't that be cool???

Unfortunately not.

to declare an asynchronous method in C# and be able to call it as WinJS.Promises we can't use the async C# keyword but instead use the IAsyncActionWithProgress interface instead. Here's an example:

namespace ClassLibrary1
{
    public sealed class Class1
    {
        public IAsyncActionWithProgress<Result> testAsync()
        {
            return AsyncInfo.Run<Result>((token, result) =>
                Task.Run<Result>(()=> 
                    {
                        // do this asynchronously ...
                        return new Result();
                    }
                
                ));
        }
    }

    public sealed class Result { ... }
}

Not as clean as one would hope, huh? Hopefully it'll change in the next Windows 8 release and Microsoft will introduce support to async keyword for WinJS.Promises

Tested on Windows 8 Consumer Preview

Steel Castro says:

2012-12-14 01:07:00 -0500

C# support many class library and much more..