AJAX - Return Arrays and Structs to your JavaScript with XML

2008-12-17T10:32:05Z

AKennard: /* Creating the XML in the WBO */

= Functionality =

The VDF AJAX Library provides the functionality for developers to call published methods within a WBO and receive a return value (for Functions). This is done using a Remote Method Invokation (RMI). Using RMI's for returning a single datatype is fairly straight-forward. If you want to return a Struct, Array , or an Array of Structs you need to do some more work. Remember, you are returning these datatypes to JavaScript and there is no direct translation from a Windows Struct or Array to a JavaScript Struct or Array.

= The Solution =

The solution is to return the data in an XML document. XML can be formatted to return a Struct of data, and Array, or an Array of Structs.

= Calling the WBO Function from JavaScript =

This is an example of a JavaScript function using the RMI to call a function of the webapp. It called the Function NameCasing of the oMyWBO. It passes a single argument of sName. When the Function returns, it will call the JavaScript method onNameCasing.

function nameCasing(sName) {
var oRMI = new VdfRemoteMethodInvocation(true, "oMyWBO", "get_NameCasing", null, onNameCasing);
oRMI.addParameter(sName);
oRMI.sendCall();
}

= Creating the XML in the WBO =

1) create an XML document 
2) add elements to the XML 
3) get the memory address of the XML document 
4) destroy the VDF connection to the address 
5) return the memory address. This will return the XML document to the JavaScript 

{ Published = True }
{ Description = "" }
Function NameCasing String sName Returns Address
Handle hoRoot hoXML hoEvent
Address aXml
// create xml document
Get Create U_cXMLDOMDocument to hoXML
Set pbValidateOnParse of hoXML to False
Get CreateDocumentElement of hoXML "response" to hoRoot
Send AddElement of hoRoot "lowercase" (lowercase(sName))
Send AddElement of hoRoot "uppercase" (Uppercase(sName))
Send AddElement of hoRoot "propercase" (Uppercase(Left(sName,1))+lowercase(Right(sName,(length(sName)-1))))
Get paXml of hoXml to aXml
Send Destroy of hoRoot
Send Destroy of hoXML
Function_Return aXML
End_Function // NameChanges

I just wanted to ask 'why' this works ....

Get paXml of hoXml to aXml
Send Destroy of hoRoot
Send Destroy of hoXML
Function_Return aXML
End_Function

Is it because VDF does not ACTUALLY destroy and objects untill it gets to end_function ? because returning a handle to something you have just destroyed doesn't look quite right ? ie you are returning a handle to nothing or something that might still exist at that point ?

VDF has a special XmlHandle return type for returning a hoXML object and the tidying up after itself

Is there a reason why this has not been used in this case ? eg would this work for AJAX ?

{ Published = True }
{ Description = "" }
Function NameCasing String sName Returns XMLHandle
Handle hoRoot hoXML hoEvent
Address aXml
// create xml document
Get Create U_cXMLDOMDocument to hoXML
Set pbValidateOnParse of hoXML to False
Get CreateDocumentElement of hoXML "response" to hoRoot
Send AddElement of hoRoot "lowercase" (lowercase(sName))
Send AddElement of hoRoot "uppercase" (Uppercase(sName))
Send AddElement of hoRoot "propercase" (Uppercase(Left(sName,1))+lowercase(Right(sName,(length(sName)-1))))
Function_Return hoXML // runtime will transfer and then destroy this object because of XMLHandle return type
End_Function // NameChanges

= Parsing the XML in JavaScript =

1) check to see if there were any errors 
2) make sure we have a return value 
3) create the XML parser object 
4) get the values from the XML

function onNameCasing(oRMI) {
// If no errors
if (oRMI.iErrorNumber==0){
if (oRMI.sReturnValue!=null){
// create XML parser
try { // code for IE
xmlDoc=new ActiveXObject("Microsoft.XMLDOM");
xmlDoc.async="false";
xmlDoc.loadXML(oRMI.sReturnValue);
} catch(e) { // code for Mozilla, Firefox, Opera, etc.
try {
parser=new DOMParser();
xmlDoc=parser.parseFromString(oRMI.sReturnValue,"text/xml");
} catch(e) {
alert(e.message);
return;
}
}
}
if (xmlDoc!=null){
var sLower="", sUpper="", sProper="";
sLower=xmlDoc.getElementsByTagName("lowercase")[0].childNodes[0].nodeValue;
sUpper=xmlDoc.getElementsByTagName("uppercase")[0].childNodes[0].nodeValue;
sProper=xmlDoc.getElementsByTagName("propercase")[0].childNodes[0].nodeValue;
//todo: do something with these values
}
}
}

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[[Category:AJAX]]

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AJAX - Return Arrays and Structs to your JavaScript with XML