Flex and .NET Web Service Error Handling

I was doing this Flex project that consumes .NET Web Service and could not figure out how to catch SOAPException from .NET Web Service.

It turns out that Flex could not read any response from the Web Service that has HTTP response code other then 200. You will get the following error (fault) from the Web Service if Flex was getting the HTTP response code other then 200:

FaultCode:Server.Error.Request
faultString:'HTTP request error'
faultDetail:'Error: [IOErrorEvent type="ioError" bubbles=false cancelable=false eventPhase=2 text="Error #2032: Stream Error.

Which is annoying because there was not specific details about the error!!

The workaround is to force .NET to return with the response status 200 if the response status code either 500 or 300.

You do this by put the following code in your application global.asax

<%@ language="C#" %>protected void Application_EndRequest(object sender,EventArgs e)
{
if(Context.Response.StatusCode==500 Context.Response.StatusCode == 300)
{
Context.Response.StatusCode = 200;
}
}

Flex dynamically create ComboBox with dataProvider from HTTPService

Well, now I am working on my own (sponsored) project during my free time. Cut the long story short, I have been working on Stock Control application for a major eBay seller in Australia. The project has been running for about 4 years now. The application is complex and fun, it supports multiple sites and items synchronization.

The existing application runs on PHP5 and MySQL. Furthermore, NUSOAP is also used to support third-party Web Service API calls to the application.

Fun has the limit for this project until I recently come out with the idea to re-design the client user interface (UI) and the integration layer to connect to the existing business/backend layer. I have decided to taste the sweetness of Flex and Zend Framework and they are awesome!

Flex uses HTTPService to asynchronously get the data from the PHP that produces XML. This XML is used to bind to a datasource for a Flex component (e.g. ComboBox). If you are using MXML tag to create the ComboBox, and assign the dataProvider to HTTPService result, you won't have issue.

However, if you need to create the ComboBox dynamically using Action Script, when you try to bind the dataSource to the XML result from the HTTPService, you will get an error saying:

Cannot access a property or method of a null object reference

This is because the execution of binding the dataSource to the XML returned from HTTPService is faster than the HTTPService itself, for example:

You have HTTPService and ComboBox objects:

1 var httpTemp:HTTPService = new HTTPService();
2 httpTemp.url = http://www.tempuri.org/xml.php;
3 httpTemp.resultFormat = "e4x";
4 httpTemp.send();
5
6 var newComboBox:ComboBox = new ComboBox();
7 newComboBox.dataProvider = httpTemp.result;

Even though line 4 is executed first, however because it takes a while to return the XML data, thus when line 7 is executed, the httpTemp.result object does not exist yet and error occurs.

To solve this:
Create a bindable vars

[Bindable] public var xmlResult:XML;
[Bindable] public var newComboBox:ComboBox;

Create a result event handler for HTTPService:

private function httpTempResultHandler( e:ResultEvent ):void
{
xmlResult = e.result as XML;
newComboBox.dataProvider = xmlResult.Category;
}

Create the ComboBox object:

//create a new instance of ComboBox
newComboBox = new ComboBox();
var httpTemp:HTTPService = new HTTPService();

Create a dummy result:

var tempString:String = '0Loading...';
xmlResult = new XML(tempString);

Create a result event listener:

httpTemp.url = "http://www.tempuri.org/xml.php";
httpTemp.resultFormat = "e4x";
//add the result event listener
httpTemp.addEventListener(ResultEvent.RESULT, httpTempResultHandler, false, 0);
httpTemp.send();

Assign the XML to the dataProvider:

newComboBox.dataProvider = xmlResult.Category;

This assigns a dummy result to the dataProvider and when the HTTPService result event handler called, the bind-able xmlResult will be used with the result from the HTTPService.