WritingXMLFiles - CocoaDev

There are four ways to write XML on OS X:

General/XmlPropertyLists by calling writeToFile:atomically:
using a third party library such as Xerces, General/IconaraDOM (see bottom for code example) or General/XMLTree
using Apple’s General/CFXMLParser API
since Tiger, using Apple’s NSXML API

This article explains the third method, using General/CFXMLParser in the General/CoreFoundation API. Here is the XML document we will be creating:

<?xml version=”1.0” encoding=”utf-8”?>

Alan Turing

The above XML is made up of a tree of General/CFXMLNode objects. The particular type of node is based on General/CFXMLNodeTypeCode. The following is a break down of the various types used in the example:

1) kCFXMLNodeTypeDocument 2) kCFXMLNodeTypeProcessingInstruction – “<?xml version=”1.0” encoding=”utf-8”?>” 3) kCFXMLNodeTypeElement – “" 4) kCFXMLNodeTypeElement -- "" 5) kCFXMLNodeTypeText -- "Alan Turing" 6) kCFXMLNodeTypeElement -- ""

** 1) Document **

We begin by creating a document node. All further nodes will be added as children to this node (xmlDocument).

General/CFXMLDocumentInfo documentInfo;
documentInfo.sourceURL = NULL;
documentInfo.encoding = kCFStringEncodingUTF8;
General/CFXMLNodeRef docNode = General/CFXMLNodeCreate(
	kCFAllocatorDefault,
	kCFXMLNodeTypeDocument,
	CFSTR(""),
	&documentInfo,
	kCFXMLNodeCurrentVersion);
General/CFXMLTreeRef xmlDocument = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault, docNode);
General/CFRelease(docNode);

** 2) Instruction Tag **

The first line of our document needs to be the <?xml /> processing instruction. Here’s how we create and add it to the document.

General/CFXMLProcessingInstructionInfo instructionInfo;
instructionInfo.dataString = CFSTR("version=\"1.0\" encoding=\"utf-8\"");
General/CFXMLNodeRef instructionNode = General/CFXMLNodeCreate(
	NULL, 
	kCFXMLNodeTypeProcessingInstruction,
	CFSTR("xml"),
	&instructionInfo,
	kCFXMLNodeCurrentVersion);
General/CFXMLTreeRef instructionTree = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault, instructionNode);
General/CFTreeAppendChild(xmlDocument, instructionTree);
General/CFRelease(instructionTree);
General/CFRelease(instructionNode);

** 3) Document’s Root Element **

The tag is the document's root element. We'll later add two sub-elements to this node. Notice how personInfo.isEmpty is set to NO. This tell General/CFXMLParser that the tag will have child nodes added to it later. If you forget to do this you output will look like this: * Alan Turing *.

General/CFXMLElementInfo personInfo;
personInfo.attributes = NULL;
personInfo.attributeOrder = NULL;
personInfo.isEmpty = NO;	
General/CFXMLNodeRef personNode = General/CFXMLNodeCreate (
   kCFAllocatorDefault,
   kCFXMLNodeTypeElement,
   (General/CFStringRef)@"person",
   &personInfo,
   kCFXMLNodeCurrentVersion);	
General/CFXMLTreeRef personTree = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault,personNode);
General/CFTreeAppendChild(xmlDocument, personTree);
General/CFRelease(personNode);

** 4) Name Sub-Element **

Now we add the name node. The text it contains is a separate node we’ll add next.

General/CFXMLElementInfo nameInfo;
nameInfo.attributes = NULL;
nameInfo.attributeOrder = NULL;
nameInfo.isEmpty = NO;	
General/CFXMLNodeRef nameNode = General/CFXMLNodeCreate (
   kCFAllocatorDefault,
   kCFXMLNodeTypeElement,
   (General/CFStringRef)@"name",
   &nameInfo,
   kCFXMLNodeCurrentVersion);	
General/CFXMLTreeRef nameTree = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault,nameNode);
General/CFTreeAppendChild(personTree, nameTree);
General/CFRelease(nameTree);
General/CFRelease(nameNode);

** 5) Text Element **

The actual value of the name element is a separate node.

General/CFXMLNodeRef nameTextNode = General/CFXMLNodeCreate (
   kCFAllocatorDefault,
   kCFXMLNodeTypeText,
   (General/CFStringRef)@"Alan Turing",
   NULL,
   kCFXMLNodeCurrentVersion);	
General/CFXMLTreeRef nameTextTree = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault,nameTextNode);
General/CFTreeAppendChild(nameTree, nameTextTree);
General/CFRelease(nameTextTree);
General/CFRelease(nameTextNode);

** 6) Adding Attributes **

In this node we’ll add an attribute. General/CFXMLElementInfo::attributes is a dictionary of attributes. The key is the attribute’s name as a string (in this case “href”). The object is the attribute’s value (in this case “http://turing.org”). General/CFXMLElementInfo::attributeOrder is a list of all the attribute names in the same order as they should be written out in the final document.

General/NSDictionary *attributeDictionary = General/[NSDictionary
   dictionaryWithObject:@"http://turing.org" forKey:@"href"];
General/NSArray *attributeArray = General/[NSArray arrayWithObject:@"href"];
General/CFXMLElementInfo websiteInfo;
websiteInfo.attributes = (General/CFDictionaryRef) attributeDictionary;
websiteInfo.attributeOrder = (General/CFArrayRef) attributeArray;
websiteInfo.isEmpty = YES;	
General/CFXMLNodeRef websiteNode = General/CFXMLNodeCreate (
   kCFAllocatorDefault,
   kCFXMLNodeTypeElement,
   (General/CFStringRef)@"website",
   &websiteInfo,
   kCFXMLNodeCurrentVersion);	
General/CFXMLTreeRef websiteTree = General/CFXMLTreeCreateWithNode(kCFAllocatorDefault,websiteNode);
General/CFTreeAppendChild(personTree, websiteTree);
General/CFRelease(websiteTree);
General/CFRelease(websiteNode);

** 7) Saving and Clean Up **

Now the final step, to write the document to disk. This is achieved with the General/CFXMLTreeCreateXMLData function. If you view the resulting xml file in a text editor you’ll notice that all the output is on one line.

General/CFDataRef xmlData = General/CFXMLTreeCreateXMLData(kCFAllocatorDefault, xmlDocument);
BOOL result = [(General/NSData *)xmlData writeToFile:@"foo.xml" atomically:YES];
General/NSAssert(result, @"Writing to file failed");
General/CFRelease(xmlData);
General/CFRelease(personTree);  // god kills a kitten every time you leak memory :-P
General/CFRelease(xmlDocument);

–General/SaileshAgrawal

Another way of doing this is to use General/XMLTree, or the DOM framework (General/IconaraDOM). Both ways are considerably simpler, and, being the author of the DOM framework, I would say that it is the prefered way of doing it.

Now, to produce the same XML-document as in the example above, do this:

id <General/DOMDocument> document; id <General/DOMElement> personElement, nameElement, websiteElement; id <General/DOMText> text; id <General/DOMAttribute> hrefAttribute;

// 1) Create a document document = General/[DOMDocument document];

// 2) Instruction tag // not necessary, will be added by the formatter

// 3) Document’s root element personElement = General/[DOMElement elementWithName:@”person”]; [document setDocumentElement:personElement];

// 4) Name subelemet nameElement = General/[DOMElement elementWithName:@”name”]; [personElement appendChild:nameElement];

// 5) Text element text = General/[DOMText textWithString:@”Alan Turing”]; [nameElement appendChild:text];

// 6) Adding attributes websiteElement = General/[DOMElement elementWithName:@”website”]; hrefAttribute = General/[DOMAttribute attributeWithName:@”href” value:@”http://turing.org”]; [websiteElement addAttribute:hrefAttribute]; [personElement appendChild:websiteElement];

// 7) Saving and cleaning up General/[DOMFormatter writeNode:document General/ToFile:@”foo.xml”];

Update: the adding the prolog is not necessary (and really an error), so that step has been removed. Update: rewrote example to work with the v2.0 interface.

This is also the way it is done in other DOM-compliant frameworks, such as DOM, JDOM and XOM for Java. If you have worked with any of these, the DOM framework for Cococa (General/IconaraDOM) will look familiar. The DOM (Document Object Model) is the prefered way of working with XML-documents if you need to insert, remove and rearrange parts of it. This can also be done with CFXML, NSXML or General/XMLTree, but it is more cumbersome.

– General/TheoHultberg/Iconara

General/XMLTree doesn’t support creating XML, correct? Maybe I’ll go ahead and do that :-)