在as3中测试xml属性的存在

Question

What is the best method to test the existence of an attribute on an XML object in ActionScript 3 ?

http://martijnvanbeek.net/weblog/40/testing_the_existance_of_an_attribute_in_xml_with_as3.html is suggesting to test using

   if ( node.@test != node.@nonexistingattribute )

and I saw comments suggesting to use:

 if ( node.hasOwnProperty('@test')) { // attribute qtest exists }

But in both case, tests are case sensitive.

From the XML Specs : "XML processors should match character encoding names in a case-insensitive way" so I presume attribute name should also be match using a case-insensitive comparison.

Thank you

Answer 1

Please re-read your quote from the XML specs carefully:

XML processors should match character encoding names in a case-insensitive way

This is in chapter 4.3.3 of the specs describing character encoding declarations , and it refers only to the names present in the encoding value of the <?xml> processing instruction, such as "UTF-8" or "utf-8" . I see absolutely no reason for this to apply to attribute names and/or element names anywhere else in the document.

In fact, there is no mention of this in section 2.3 of the specs, Common Syntactic Constructs , where names and name tokens are specified. There are a few restrictions on special characters and such, but there is absolutely no restriction on upper and lower case letters .

To make your comparison case-insensitive, you will have to do it in Flash:

for each ( var attr:XML in xml.@*) {
   if (attr.name().toString().toLowerCase() == test.toLowerCase()) // attribute present if true
}

or rather:

var found:Boolean = false;
for each ( var attr:XML in xml.@*) {
    if (attr.name().toString().toLowerCase() == test.toLowerCase()) {
        found = true;
        break;
    }
}
if (found) // attribute present
else // attribute not present

Answer 2

How about using XML's contains() method or XMLList's length() method ?

eg

var xml:XML = <root><child id="0" /><child /></root>;

trace(xml.children().@id.length());//test if any children have the id attribute
trace(xml.child[1].@id.length());//test if the second node has the id attribute
trace(xml.contains(<nephew />));//test for inexistend node using contains()
trace(xml.children().nephew.length());//test for inexistend node using legth()