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How to parse main XML file using NSXMLParser?

I'm trying to figure out the NSXMLParser for my iPhone application, and while I usually understand how it works, I'm still a little confused about how to retrieve the values ​​I want.

The XML output I am processing is very simple. This is true:

<start>
 <status>300</status>
 <record>
  <title>The Title</title>
  <content>Some content</content>
 </record>
</start>

I need to do 3 things: Get the status value. Get content value from your first post. There may be an answer that suggests multiple "entry" items, so I only need to get the first one.

I cannot figure out how to do this. Most of all the examples I have seen involve creating a separate object to populate this data, and I don't see that this is needed for 2 values. Can anyone tell me how to pull these 2 pieces of data and for the first record only?

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2 answers


The first thing that happens when an NSXMLParser

XML tag is encountered is the delegate method is called parser:didStartElement:namespaceURI:qualifiedName:attributes:

; you will probably need to use a variable here elementName

. The XML parser then reads the characters in the tag and calls the parser:foundCharacters:

content. Finally called parser:didEndElement:namespaceURI:qualifiedName

.

The approach I have taken, as Apple uses in the SeismicXML example, is to use methods like this:

  • In, parser:didStartElement:namespaceURI:qualifiedName:attributes:

    compare the element name string with a known value to see if you need a string. If so, then set the instance variable (a NSMutableString

    ; I'll call it contentOfCurrentXMLProperty

    ) to an empty string. Otherwise, set it to nil

    .
  • In parser:foundCharacters:

    add the found symbols to contentOfCurrentXMLProperty

    .
  • In, parser:didEndElement:namespaceURI:qualifiedName

    assign a value contentOfCurrentXMLProperty

    to whatever corresponds to the corresponding variable.


See the SeismicXML example for more information.

A couple of things about your particular case: First, since the XML parser only returns strings, you need to convert the string to an integer (or whatever data type you use) for status

.

Second, since you only need the first value for record

, parser:didStartElement:...

I would set in BOOL

, which indicates that you have already seen the tag record

before and, if so, set contentOfCurrentXMLProperty

before nil

.

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Keeping in mind that NSXMLParser is an event-based SAX-like parser, you must configure your parser, run it, and listen for key events.

Install the parser up:

NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
[parser setDelegate:self];
[parser parse];

Cancel the following methods:

– parser:didStartElement:namespaceURI:qualifiedName:attributes:
– parser:didEndElement:namespaceURI:qualifiedName:
– parser:foundCharacters:

Your function should basically say:

  • When you reach the next tag run:

-(void)parser: didStartElement:(NSString *) namespaceURI:(NSString *) qualifiedName:(NSString *) attributes:(NSDictionary *)

  • If the name of this tag is "status":


[elementName isEqualToString:@"status"]

  • Give me the tag line data:

- (void)parser:(NSXMLParser *) foundCharacters:(NSString *)

...

[<your statusValueHolder as NSMutableString> appendString:<foundCharacters' parameter>]

...

You can apply the same logic for a different case (search for the first run tag named "record", abort until the end of the tag named "record", etc.)

Take a look at this and try it at home: Make NSXMLParser your friend .. Also see the NSXMLParser API References for additional delegation methods for the NSXMLParser delegate.

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