interesting service behaviour in silverlight

I have a Silverlight project which takes some encrypted string thr开发者_Python百科u its Service Reference: DataService (service which is done in an ASP.NET project).

The method from TransactionServices.cs to get the encrypted string is:

 public void GetEncryptedString(string original)
    {
        DataService.DataServiceClient dataSvc = WebServiceHelper.Create();
        dataSvc.GetEncryptedStringCompleted += new EventHandler<SpendAnalyzer.DataService.GetEncryptedStringCompletedEventArgs>(dataSvc_GetEncryptedStringCompleted);
        dataSvc.GetEncryptedStringAsync(original);
    }

On completing, put the result in encodedString var (which is initialized with an empty value):

void dataSvc_GetEncryptedStringCompleted(object sender, SpendAnalyzer.DataService.GetEncryptedStringCompletedEventArgs e)
    {
        if (e.Error == null)
        {
            try
            {
                if (e.Result == null) return;
                this.encodedString = e.Result;
            }
            catch (Exception ex)
            {
                Logger.Error("TransactionService.cs: dataSvc_GetEncryptedStringCompleted: {0} - {1}",
                    ex.Message, ex.StackTrace);
                MessageBox.Show(ex.ToString());
            }
        }
    }

Now I want to get the encoded string from my MainPage.xaml like:

TransactionService ts = new TransactionService();
                    ts.GetEncryptedString(url);
                    Console.WriteLine(ts.encodedString);

I do not uderstand why ts.encodedString is empty. When I do the debug I see that it actually prints out empty and AFTER that it goes to the void dataSvc_GetEncryptedStringCompleted to take the result and fill it.

Can you point me what I've done wrong? Is there a way to wait for the encodedString to be fetched and only after that to continue?

Thanks a lot.

When you call the ts.GetEncryptedString(url); you just started async operation. And therefor the value you are accessing is will be set only in the callback method.

But you access it before the value is modified by the callback.

The solution which I am using will looks similar to folowing:

Redefine the GetEncryptedString method signature.

public void GetEncryptedString(string original, Action callback)
    {
        DataService.DataServiceClient dataSvc = WebServiceHelper.Create();
        dataSvc.GetEncryptedStringCompleted += (o,e) => 
{
dataSvc_GetEncryptedStringCompleted(o,e); 
callback(); 
}            
        dataSvc.GetEncryptedStringAsync(original);
    }

Call it like this:

ts.GetEncryptedString(url, OtherLogicDependantOnResult);

where

OtherLogicDependantOnResult is

void OtherLogicDependantOnResult()
{
//... Code
}