如何创建一个API方法来读取iPhone中的XML数据？

Question

我正在创建一个基于 XML 的应用程序，其中我必须从 XML 获取数据并在 iPhone 上显示。我有一个正在获取数据的网址。但我不知道如何创建用于 XML 解析的 API 方法。

如何创建一个API方法来确定url返回的数据是XML格式还是JSON格式？

Answer 1

请参阅 Apple 的 XMLPerformance 项目以获取示例代码。

Answer 2

您必须使用 NSXMLParser

Answer 3

您不需要创建自定义 API。查看 NSXMLParser 和 libxml2。这方面并不差，你只需要学会使用它即可。一旦你看到代码，它应该从

Answer 4

有一个关于如何使用 NSXML 解析器的很好的教程

您基本上会对 didStart 和 didEndelements 感兴趣。当文档解析结束时，会调用不同的方法。

Answer 5

这是我在项目中使用的 xml 解析器代码，它应该允许您解析大多数 XML 文件：

//
//  XMLParser.h
//

#import <Foundation/Foundation.h>
#import "XMLNode.h"

#if __IPHONE_OS_VERSION_MAX_ALLOWED > __IPHONE_3_2
@interface XMLParser : NSObject <NSXMLParserDelegate> {
#else
@interface XMLParser : NSObject {
#endif
    XMLNode *rootElement;
    XMLNode *tempElement;
    NSMutableString *temp;
    NSMutableArray *elements;
}

- (NSObject *)parseData:(NSData *)data;

// NSXMLParser delegate implementation
- (void)parserDidStartDocument:(NSXMLParser *)parser;
- (void)parserDidEndDocument:(NSXMLParser *)parser;
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName attributes:(NSDictionary *)attributeDict;
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName;
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string;

@end

-

//
//  XMLParser.m
//

#import "XMLParser.h"


@implementation XMLParser

- (NSObject *)parseData:(NSData *)data
{
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
    [parser setDelegate:self];
    [parser setShouldResolveExternalEntities:YES];

    if (![parser parse]) {
        if ([[parser parserError] code] == NSXMLParserUnknownEncodingError) {
            // If encoding is "us-ascii" replace encoding with something known (as NSXMLParser is not supporting this encoding)
            NSString *oldString = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
            NSString *newEncodingString = [oldString stringByReplacingOccurrencesOfString:@"encoding=\"us-ascii\"" withString:@"encoding=\"iso-8859-1\"" options:0 range:NSMakeRange(0,100)];
            newEncodingString = [newEncodingString stringByReplacingOccurrencesOfString:@"encoding=\"windows-1251\"" withString:@"encoding=\"iso-8859-1\"" options:0 range:NSMakeRange(0,100)];

            [oldString release];
            NSData *nameData = [newEncodingString dataUsingEncoding:NSASCIIStringEncoding];
            NSXMLParser *parser2 = [[NSXMLParser alloc] initWithData:nameData];
            [parser2 setDelegate:self];
            [parser2 setShouldResolveExternalEntities:YES];
            if (![parser2 parse]) {
                DLog(@"parseXML error : %@",[[parser2 parserError] localizedDescription]);
            }
            [parser2 release];

        } else {
            DLog(@"parseXML error : %@",[[parser parserError] localizedDescription]);
        }

    }
    [parser release];

    return rootElement;
}


- (void)dealloc
{
    if (tempElement != nil) {
        [tempElement release];
    } 
    if (rootElement != nil) {
        [rootElement release];
    }
    if (temp != nil) {
        [temp release];
    }
    if (elements != nil) {
        [elements release];
    }

    [super dealloc];
}


// NSXMLParser delegate implementation


- (void)parserDidStartDocument:(NSXMLParser *)parser
{
    if (elements != nil) {
        [elements release];
    }
    elements = [[NSMutableArray alloc] init];
    if (tempElement != nil) {
        [tempElement release];
        tempElement = nil;
    }
    if (temp != nil) {
        [temp release];
        temp = nil;
    }
    if (rootElement != nil) {
        [rootElement release];
        rootElement = nil;
    }
}


- (void)parserDidEndDocument:(NSXMLParser *)parser
{
   if (elements != nil) {
        [elements release];
        elements = nil;
    }
    if (tempElement != nil) {
        [tempElement release];
        tempElement = nil;
    }
    if (temp != nil) {
        [temp release];
        temp = nil;
    }
}


- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName
  namespaceURI:(NSString *)namespaceURI
 qualifiedName:(NSString *)qualifiedName
    attributes:(NSDictionary *)attributeDict
{
    XMLNode *element = [[[XMLNode alloc] initWithName:elementName] autorelease];
    [element setAttributes:attributeDict];
    if (tempElement != nil) {
        [tempElement addChild:element];
        [elements addObject:tempElement];
        [tempElement release];
    } else {
        rootElement = [element retain];
    }

    tempElement = [element retain];
    if (temp != nil) {
        [temp release];
    }
    temp = [[NSMutableString alloc] init];
}


- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
  namespaceURI:(NSString *)namespaceURI
 qualifiedName:(NSString *)qName
{
    [tempElement setContent:temp];
    [temp release];
    temp = nil;
    [tempElement release];
    tempElement = nil;
    if ([elements count] > 0) {
        tempElement = [[elements lastObject] retain];
        [elements removeLastObject];
    }
}


- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    if (temp != nil) {
        [temp appendString:string];
    }
}

@end

-

//
//  XMLNode.h
//

#import <Foundation/Foundation.h>

/**
 * XMLNode represents an XML data node.
 *
 * Every node can contain multiple childs, attributes, a content string
 * and an element name. An XML document is represented using a reference
 * to the document root node.
 * @ingroup Webservice
 */
@interface XMLNode : NSObject {

    NSMutableArray *childs;
    NSDictionary *attributes;
    NSString *content;
    NSString *elementName;

}

/**
 * Return an initialized XMLNode.
 * @param name The element name of the node.
 */
- (id)initWithName:(NSString *)name;

/**
 * Set the node attributes.
 * @param dictionary A dictionary containing the attributes.
 */
- (void)setAttributes:(NSDictionary *)dictionary;

/**
 * Set the content as string.
 * @param string The content as string.
 */
- (void)setContent:(NSString *)string;

/**
 * Add a child node.
 * @param xmlElement The child node.
 */
- (void)addChild:(XMLNode *)xmlElement;

/**
 * Return a specific attribute.
 * @param name The attribute name.
 * @return The attribute for the specified name or nil.
 */
- (NSString *)attributeForName:(NSString *)name;

/**
 * Return a child at a specific index.
 * 
 * If the index is out of the bounds, an NSRangeException is thrown.
 * @param index The position of the child (by document order).
 * @return The child at index
 * @see childElementsCount
 */
- (XMLNode *)childElementAtIndex:(int)index;

/**
 * Return a child with a certain name.
 * @param name The name of the element.
 * @return The element or nil if not available.
 */
- (XMLNode *)childWithName:(NSString *)name;
- (XMLNode *)childWithName:(NSString *)name atIndex:(NSInteger)index;

/** 
 * Return the number of child nodes.
 * @return The number of child nodes.
 */
- (int)childElementsCount;
- (int)childWithNameElementsCount:(NSString *)name;

/** 
 * Return the node content.
 * @return The node content as string.
 */
- (NSString *)content;

/**
 * Get the name of the xml element.
 * @return The name of the element.
 */
- (NSString *)name;

- (void)dealloc;

@end

-

//
//  XMLNode.m
//

#import "XMLNode.h"


@implementation XMLNode
- (id)initWithName:(NSString *)name
{
    self = [super init];
    elementName = [name copy];
    childs = [[NSMutableArray alloc] init];
    return self;
}


- (void)setAttributes:(NSDictionary *)dictionary
{
    if (attributes != nil) {
        [attributes release];
    }
    attributes = [dictionary retain];
}


- (void)setContent:(NSString *)string
{
    if (content != nil) {
        [content release];
    }
    content = [string retain];
}

- (void)addChild:(XMLNode *)xmlElement
{
    [childs addObject:xmlElement];
}


- (NSString *)attributeForName:(NSString *)name
{
    return [attributes objectForKey:name];
}


- (XMLNode *)childElementAtIndex:(int)index
{
    return [childs objectAtIndex:index];
}


- (XMLNode *)childWithName:(NSString *)name
{
    int i;
    for (i=0; i<[childs count]; ++i) {
        XMLNode *child = [childs objectAtIndex:i];
        if ([[[child name] lowercaseString] isEqualToString:[name lowercaseString]]) {
            return child;
        }
    }

    return nil;
}

- (XMLNode *)childWithName:(NSString *)name atIndex:(NSInteger)index
{
    int i;
    int count = 0;
    for (i=0; i<[childs count]; ++i) {
        XMLNode *child = [childs objectAtIndex:i];
        if ([[[child name] lowercaseString] isEqualToString:[name lowercaseString]]) {
            if (count == index)
                return child;
            count ++;
        }
    }

    return nil;
}

- (int)childElementsCount
{
    return [childs count];
}

- (int)childWithNameElementsCount:(NSString *)name
{
    int i;
    int count = 0;
    for (i=0; i<[childs count]; ++i) {
        XMLNode *child = [childs objectAtIndex:i];
        if ([[[child name] lowercaseString] isEqualToString:[name lowercaseString]]) {
            count ++;
        }
    }

    return count;
}


- (NSString *)content
{
    return content;
}


- (NSString *)name
{
    return elementName;
}


- (void)dealloc
{
    if (content != nil) {
        [content release];
    }
    if (childs != nil) {
        [childs release];
    }
    if (attributes != nil) {
        [attributes release];
    }

    [super dealloc];
}

@end

按以下方式使用（此示例用于分析 rss feed：

XMLParser *parser = [[XMLParser alloc] init];
NSObject *rss = [parser parseData:rssFeed];
feedItems = [(XMLNode *)rss childWithName:@"channel"];
if (feedItems) {
    NSLog(@"%@",[[feedItems childWithName:@"title"] content]);
}
[parser release];

如果您想了解更多方法，请检查 XMLNode.h需要更复杂的分析

Answer 6

听起来您的问题不是如何解析 XML，而是如何从 Web 下载 XML 文档到 NSData 对象等。

您可以使用开源的ASIHTTPRequest框架快速下载您的XML数据。查看有关设置异步请求的操作文档 。

假设 URL 正确并且请求成功，XML 数据将存储在请求的 responseData 属性中。

然后，您可以使用各种方法来解析此属性中的 XML 数据。我推荐 libxml2，因为它是最快的。但此时您可以使用任何您想要的解析器引擎和方法。