在WP8 / Silverlight中调用Async方法时，是否可以传递回调

Question

I've been writing Windows Phone 8 code that calls a SOAP web service backend. From what I've read, the typical pattern is this:

var client = new KitchenPCSoapClient();

client.LogonCompleted += client_LogonCompleted;
client.LogonAsync(username, password);

To me, this just seems counter intuitive. If I call LogonAsync multiple times with the same client, I don't necessarily want it to use the same LogonCompleted callback every time.

What I'd like is a pattern more like JavaScript, where you pass in a reference to the callback function. More like:

var client = new KitchenPCSoapClient();
client.LogonAsync(username, password, client_LogonCompleted);

Is there a way to implement such a pattern, or should I just force myself to get used to setting the LogonCompleted property before I call LogonAsync , or set the userState property if I want to differentiate between different contexts?

Answer 1

You can make use of Dispatcher and call the function on UI side for this ...

I am doing like this

callback function

private void AddPricesHandler(CompletedEventArgs response, Exception e)
{
  //your code gose here
}

Call proxy calss function

Proxy.AddData(AddPricesHandler, request);

proxy class calling webservice

public void AddData(Action<CompletedEventArgs, Exception> callback, IPVWorkflowService.CreateEditDeletePriceSourceRequest request)
        {
            _workflowProxy.CreateEditDeletePriceSourceAsync(request, callback);
            _workflowProxy.CreateEditDeletePriceSourceCompleted+=new EventHandler<CreateEditDeletePriceSourceCompletedEventArgs>(_workflowProxy_CreateEditDeletePriceSourceCompleted); 
        }

completer function use dispatcher to call callback function

    void _workflowProxy_CreateEditDeletePriceSourceCompleted(object sender, CreateEditDeletePriceSourceCompletedEventArgs e)
    {
        try
        {
            this.dispatcher.BeginInvoke((Action)(() =>
            {
                (e.UserState as Action<CompletedEventArgs, Exception>)(e, null);
            }));
        }
        catch (Exception ex)
        {
            this.dispatcher.BeginInvoke((Action)(() =>
            {
                (e.UserState as Action<CompletedEventArgs, Exception>)(e, ex);
            }));
        }
        finally
        {
            _workflowProxy.CreateEditDeletePriceSourceCompleted -= _workflowProxy_CreateEditDeletePriceSourceCompleted;
            _workflowProxy = null;
        }
    }

Answer 2

The beauty of Async/Await is that you don't have to write callbacks, you just write code that looks like synchronous, but in the background it's executed asynchronously:

var client = new KitchenPCSoapClient();
await client.LogonAsync(username, password);

// you get here after the async logon is completed
// do stuff after logon

But if you really want to use callbacks, you can just use the method ContinueWith on the Task object, that is returned from asynchronous method:

var client = new KitchenPCSoapClient();
Task task = client.LogonAsync(username, password);

// this method is called when async execution of task is finished
task.ContinueWith(client_LogonCompleted);