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You will need to know this at some point if you are interacting with SOAP in Flex, I guarantee it.


Types registered in SchemaTypeRegistry may overlap across different services.


You have a UserService and a RoleService. Methods for both services return an ArrayOfString. This type is generated by Flex when you import the service into the project. You call methods for each service simultaneously that both return an ArrayOfString. However, you get a type coercion problem. Why?


When Flex imports a web service, it generates a Base{ServiceName} class. In this class, it registers types (like ArrayOfString) with a singleton called SchemaTypeRegistry when the service is instantiated. The problem is, it doesn’t qualify which ArrayOfString it’s talking about.

Therefore, when you instantiate UserService and call a method that returns ArrayOfString, the BaseUserService will map ArrayOfString to net…userservice.ArrayOfString. This works just great when you aren’t making asynchronous calls.

The problem arises when you make asynchronous calls to both UserService AND RoleService. The last service to register ArrayOfString with its corresponding ActionScript class wins. Then, when the result for the other service returns, it will try to explicitly cast a net…userservice.ArrayOfString to a net…roleservice.ArrayOfString and you will net a null result. It won’t error, because it uses the “as” keyword vs, an explicit cast (i.e. result as ArrayOfString, vs ArrayOfString(result)), which makes debugging even more mysterious.


In my opinion, this is truly a bug in the framework vs a limitation. If you can make asynchronous calls, you should be able to asynchronously deserialize the results, plain and simple. However, we’ve only really found two plausible workarounds.

“Doctor, it hurts when I sit this way.”

“Then don’t sit that way.”

One workaround is to simply queue the calls. Wait until the first call returns, then instantiate the next web service and make the second call.

If you are into changing your back end to patronize the front end, you will need to make the return type unique.

Bon apetit.



MyMethod can’t return an object of with the type name MyMethodResult.


If you have a ListUsers class, and you return an object of type ListUsersResult, your code will compile but your application will break.


Again, the problem lies in the Base{Service} generated class. The result wrapper will not generate properly if you name your result object in this manner.


Again, don’t sit that way. You simply cannot append “Result” to the end of your result object if it is named the same as the method itself.



Headers array gets overwritten.


You try to make a method call, but it sends an empty headers array, even after you’ve set the headers. 


When Flex generates the method functions abstraction classes for your service, instead of “passing along the headers” as the ASDoc would indicate, it simply creates an empty array. Can you guess where this is found. Correct! The Base{Service} class. The first line after the method signature will be “var headerArray:Array = new Array();”.


We have to remember to do a global search and replace for “var headerArray:Array = new Array();” replaced with “var headerArray:Array = this.headers;” each time we regenerate the web service abstraction classes when we need to preserve headers for method calls.



You can’t have a service with a method named .logout()


If you name your method “logout” (i.e. for an authentication class), your generated class won’t compile.


The inheritance chain for the web service abstraction classes is: MyService HAS BaseCubeReportService EXTENDS AbstractWebService EXTENDS AbstractService HAS AsyncRequest. AbstractService has a public function logout():void that calls the logout() method of it’s asyncRequest object. When Flex Builder attempts to generate the logout abstraction method in your service class, it will error as though you were trying to override this function.


Again, avoid usage of “logout”.


I sincerely hope this saves you the hours of debugging that we invested to gain this knowledge.



  1. I thought this was a crazy old post — refering to Flex Data Services (now known as LiveCycle Data Services).

    I’ve never liked the webservice wizard generator. By writing the classes by hand, most of the stuff you wrote above goes away 🙂

  2. I updated the title to clarify. In an enterprise system with hundreds of methods, obviously writing the abstraction classes by hand not only doubles your initial write time, but also the effort when you have to update a method. One would think that the functionality to generate these abstracted classes was created for such a reason. Of course if you write things by hand, you’ll have the ultimate control and avert these types of automation issues, however, the quicker mundane tasks can be automated, the more development effort can be applied to actually innovating on the software itself.

    The same logic could be said of Flex itself–I could choose to write my own UIComponent set for each application I write as well, and avoid the bugs in the Flex UI framework. MXML is intrinsically a code generator.

    But I digress. Thanks for your comments.

  3. This was an extremely helpful post, thanks for publishing it.

    I’m building a proof of concept/prototype UI for an existing application that happens to have a bunch of ServiceMethodResult contracts in it’s services… so I hit Issue #2 within hours of getting started with Flex. I really hope Adobe fixes these issues.

  4. Here’s another one: when the return value is an array and the method returns null, instead of getting null in the result you will receive an array with length=1 and the first element value is null…

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