我正在创建一个基于 XML 的应用程序，我必须在其中从 XML 获取数据并在 iPhone 上显示。我有一个获取数据的 url。但是我不知道如何创建用于 XML 解析的 API 方法。
如何创建 API 方法来确定 url 返回的数据是 XML 格式还是 JSON 格式？
【问题讨论】：
标签： iphone objective-c
查看 Apple 的 XMLPerformance 项目以获取示例代码。
【讨论】：
你必须使用NSXMLParser
【讨论】：
您无需创建自定义 API。查看 NSXMLParser 和 libxml2。这还不错，你只需要学会使用它。一旦你看到它应该编写的代码
【讨论】：
关于如何使用 NSXML 解析器 here 有一个很好的教程。 您必须实现解析器委托并从这些委托方法中获取解析值。
您基本上会对 didStart 和 didEndelements 感兴趣。文档解析结束时调用不同的方法。
【讨论】：
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
如下使用（此示例用于分析 rss 提要：
XMLParser *parser = [[XMLParser alloc] init];
NSObject *rss = [parser parseData:rssFeed];
feedItems = [(XMLNode *)rss childWithName:@"channel"];
if (feedItems) {
NSLog(@"%@",[[feedItems childWithName:@"title"] content]);
}
[parser release];
如果您需要更复杂的分析，请查看 XMLNode.h 以获取更多方法
【讨论】：
听起来您的问题不是如何解析 XML，而是如何将 XML 文档从 Web 下载到 NSData 对象等中。
您可以使用开源的ASIHTTPRequest 框架快速下载您的XML 数据。看看how-to document on setting up an asynchronous request。
假设 URL 正确且请求成功，则 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。
【讨论】：