User Guide

522 Using the External API

The External API’s XML format

Communication between ActionScript and an application hosting the Shockwave Flash

ActiveX control uses a specific XML format to encode function calls and values. In the

Introvert IM C# example, the ExternalInterfaceProxy class makes it possible for the code in

the application form to ignore this format and operate directly on the values. In order to

accomplish this, the ExternalInterfaceProxy class uses the methods of the

ExternalInterfaceSerializer class to actually translate the XML messages into .NET objects.

The ExternalInterfaceSerializer class has four public methods:

■ EncodeInvoke() Encodes a function name and a C# ArrayList of arguments into the

appropriate XML format.

■ EncodeResult() Encodes a result value into the appropriate XML format.

■ DecodeInvoke() Decodes a function call from ActionScript. The FlashCall event

object’s

request property is passed to the DecodeInvoke() method, and it translates the

call into an ExternalInterfaceCall object.

■ DecodeResult() Decodes the XML received as the result of calling an ActionScript

function.

There are two parts to the XML format used by the External API. One format is used to

represent function calls. Another format is used to represent individual values; this format is

used for parameters in functions as well as function return values. The XML format for

function calls is used for calls to and from ActionScript. For a function call from ActionScript,

Flash Player passes the XML to the container; for a call from the container, Flash Player

expects the container application to pass it an XML string in this format. The following XML

fragment shows an example XML-formatted function call:

... (individual argument values)

</arguments>

</invoke>

The root node is the <invoke> node. It has two attributes: name indicates the name of the

function to call, and

returntype is always xml. If the function call includes parameters, the

<invoke> node has a child <arguments> node, whose child nodes will be the parameter

values formatted using the individual value format explained next.