R – Flex 3.2 casting problem

actionscript-3apache-flexcasting

I'm newish to flex an have recently hit a snag casting.

this is the code I'm running.

/**
* return background definition depending on time
*/ 
private function findBackgroundItem( relativeTime : Number ) : CSBackgroundItem
{
    if( this.backgroundItems == null ) return null;
    var result :CSBackgroundItem = null;
    var relative:Date = new Date(relativeTime);
    for( var i : Number = 0; i < this.backgroundItems.length; i++ )
    {
        // backgroundItems is an Ilist of CSBackgroundItem.
        var colourItem : CSBackgroundItem = CSBackgroundItem( this.backgroundItems.getItemAt( i ) );

        // other stuff here
    }           
    return result;
}

The problem occurs when the IList.getItemsAt() result is cast to the CSBackgroundItem variable colourItem. The following error is thrown

TypeError: Error #1034: Type Coercion failed: cannot convert com.mystuff::CSBackgroundItem@650e8dd1 to com.mystuff.CSBackgroundItem.

If I use the 'as' keyword I get cast results in the colourItem being null. Using the debugger shows that the list is not empty and is indeed populated with CSBackgroundItem objects.

Now this is the wacky bit.. this code works, the first time the module it's in loads.. subsequent loads (after unloading it) throw the exception.

Can anyone shed any light on why this might happen?

Best Answer

FYI, a type loaded into a child ApplicationDomain can be cast to a type (that it extends/implements) in the parent ApplicationDomain.

Eg.

loader.applicationDomain = ApplicationDomain.currentDomain; // parent domain
loader.applicationDomain = new ApplicationDomain(ApplicationDomain.currentDomain); // child domain
loader.applicationDomain = new ApplicationDomain(); // new domain

Related Solutions

C# – Direct casting vs ‘as’ operator

string s = (string)o; // 1

Throws InvalidCastException if o is not a string. Otherwise, assigns o to s, even if o is null.

string s = o as string; // 2

Assigns null to s if o is not a string or if o is null. For this reason, you cannot use it with value types (the operator could never return null in that case). Otherwise, assigns o to s.

string s = o.ToString(); // 3

Causes a NullReferenceException if o is null. Assigns whatever o.ToString() returns to s, no matter what type o is.

Use 1 for most conversions - it's simple and straightforward. I tend to almost never use 2 since if something is not the right type, I usually expect an exception to occur. I have only seen a need for this return-null type of functionality with badly designed libraries which use error codes (e.g. return null = error, instead of using exceptions).

3 is not a cast and is just a method invocation. Use it for when you need the string representation of a non-string object.

R – Parse Error When Trying to Set a Break in Flex 3

Update: Cool, you've got your code compiled! Try with the following:

Set resultFormat=array if you have an array of objects. Get this value in an array and loop over to see if you have can see the items. If this doesn't work try next tip.
Remove the resultFormat from the HTTPService tag (which is the same as if you had set it to object). See this.

The functions in AS typically go inside a <mx:Script> tag. That's the first thing to fix. You will also have to import the definitions of the classes you are using. Have a look here:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" 
                layout="absolute" width="535" height="345"
                creationComplete="getData.send()">
<mx:Script>
  <![CDATA[
 import mx.rpc.events.FaultEvent;
 import mx.rpc.events.ResultEvent;
 import mx.controls.Alert;
     import mx.rpc.http.HTTPService;

 private function resultHandler(e:ResultEvent):void {
    Alert(e.result.toString());
 }
 private function faultHandler(e:FaultEvent):void {
    Alert(e.fault.toString());
 }
  ]]>
 </mx:Script>
<mx:HTTPService id="getData" resultFormat="text" 
                fault="faultHandler(event)" result="resultHandler(event)"   
                url="http://www.myurl.com"/>
</mx:Application>

Try using this MXML file and let us know how far you got.

Best Answer

Related Solutions

C# – Direct casting vs ‘as’ operator

R – Parse Error When Trying to Set a Break in Flex 3

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