［Object C］object c中完成將xml轉換為json

參考：http://troybrant.net/blog/2010/09/simple-xml-to-nsdictionary-converter/

現在只知道了怎麼用，具體原理還有待深究。

將xml轉換為json，分為兩步：

1.將xml轉換為NSDictionary。

2.將NSDictionary 轉換為json 

#import <Foundation/Foundation.h>

@interface XMLReader : NSObject
{
    NSMutableArray *dictionaryStack;
    NSMutableString *textInProgress;
    NSError **errorPointer;
}

+ (NSDictionary *)dictionaryForXMLData:(NSData *)data error:(NSError **)errorPointer;
+ (NSDictionary *)dictionaryForXMLString:(NSString *)string error:(NSError **)errorPointer;
+ (NSString *)jsonStringForXMLDictionary:(NSDictionary *)dictionary error:(NSError **)errorPointer;


@end

#import "XMLReader.h"

NSString *const kXMLReaderTextNodeKey = @"text";

@interface XMLReader (Internal)

- (id)initWithError:(NSError **)error;
- (NSDictionary *)objectWithData:(NSData *)data;

@end

@implementation XMLReader

#pragma mark -
#pragma mark Public methods

+ (NSDictionary *)dictionaryForXMLData:(NSData *)data error:(NSError **)error
{
    XMLReader *reader = [[XMLReader alloc] initWithError:error];
    NSDictionary *rootDictionary = [reader objectWithData:data];
    [reader release];
    return rootDictionary;
}

+ (NSDictionary *)dictionaryForXMLString:(NSString *)string error:(NSError **)error
{
    NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
    return [XMLReader dictionaryForXMLData:data error:error];
}

//added by chenjie
+ (NSString *)jsonStringForXMLDictionary:(NSDictionary *)dictionary error:(NSError **)error
{
//    NSDictionary *dictionary = [XMLReader dictionaryForXMLString:testXMLString error:&parseError];
    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictionary options:NSJSONWritingPrettyPrinted
                        //pass 0 if you don't care about the readability of the generated string
                                                         error:error];
    if(!jsonData)
    {
        NSLog(@"Got an error:%@",*error);
        return  nil;
    }
    else
    {
       return  [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
//        NSLog(@"%@", jsonString);
    }
    
}

#pragma mark -
#pragma mark Parsing

- (id)initWithError:(NSError **)error
{
    if (self = [super init])
    {
        errorPointer = error;
    }
    return self;
}

- (void)dealloc
{
    [dictionaryStack release];
    [textInProgress release];
    [super dealloc];
}

- (NSDictionary *)objectWithData:(NSData *)data
{
    // Clear out any old data
    [dictionaryStack release];
    [textInProgress release];
    
    dictionaryStack = [[NSMutableArray alloc] init];
    textInProgress = [[NSMutableString alloc] init];
    
    // Initialize the stack with a fresh dictionary
    [dictionaryStack addObject:[NSMutableDictionary dictionary]];
    
    // Parse the XML
    NSXMLParser *parser = [[NSXMLParser alloc] initWithData:data];
    parser.delegate = self;
    BOOL success = [parser parse];
    
    // Return the stack’s root dictionary on success
    if (success)
    {
        NSDictionary *resultDict = [dictionaryStack objectAtIndex:0];
        return resultDict;
    }
    
    return nil;
}

#pragma mark -
#pragma mark NSXMLParserDelegate methods

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
    // Get the dictionary for the current level in the stack
    NSMutableDictionary *parentDict = [dictionaryStack lastObject];
    
    // Create the child dictionary for the new element, and initilaize it with the attributes
    NSMutableDictionary *childDict = [NSMutableDictionary dictionary];
    [childDict addEntriesFromDictionary:attributeDict];
    
    // If there’s already an item for this key, it means we need to create an array
    id existingValue = [parentDict objectForKey:elementName];
    if (existingValue)
    {
        NSMutableArray *array = nil;
        if ([existingValue isKindOfClass:[NSMutableArray class]])
        {
            // The array exists, so use it
            array = (NSMutableArray *) existingValue;
        }
        else
        {
            // Create an array if it doesn’t exist
            array = [NSMutableArray array];
            [array addObject:existingValue];
            
            // Replace the child dictionary with an array of children dictionaries
            [parentDict setObject:array forKey:elementName];
        }
        
        // Add the new child dictionary to the array
        [array addObject:childDict];
    }
    else
    {
        // No existing value, so update the dictionary
        [parentDict setObject:childDict forKey:elementName];
    }
    
    // Update the stack
    [dictionaryStack addObject:childDict];
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    // Update the parent dict with text info
    NSMutableDictionary *dictInProgress = [dictionaryStack lastObject];
    
    // Set the text property
    if ([textInProgress length] > 0)
    {
        // Get rid of leading + trailing whitespace
        [dictInProgress setObject:textInProgress forKey:kXMLReaderTextNodeKey];
        
        // Reset the text
        [textInProgress release];
        textInProgress = [[NSMutableString alloc] init];
    }
    
    // Pop the current dict
    [dictionaryStack removeLastObject];
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    // Build the text value
    [textInProgress appendString:string];
}

- (void)parser:(NSXMLParser *)parser parseErrorOccurred:(NSError *)parseError
{
    // Set the error pointer to the parser’s error object
    *errorPointer = parseError;
}

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

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        
        // insert code here...
        NSLog(@"Hello, World!");
        //convert xml to NSDictionary
//        NSString *testXMLString = @"<items><item id=\"0001\" type=\"donut\"><name>Cake</name><ppu>0.55</ppu><batters><batter id=\"1001\">Regular</batter><batter id=\"1002\">Chocolate</batter><batter id=\"1003\">Blueberry</batter></batters><topping id=\"5001\">None</topping><topping id=\"5002\">Glazed</topping><topping id=\"5005\">Sugar</topping></item></items>";
        
        NSString *testXMLString = @"<sentence content1=\"sent\"><word content2=\"wor\"/></sentence>";
        
        // Parse the XML into a dictionary
        NSError *xmlConvert2DictError = nil;
        NSError *dictConvert2StringError = nil;
        NSDictionary *xmlDictionary = [XMLReader dictionaryForXMLString:testXMLString error:&xmlConvert2DictError];
        
        // Print the dictionary
        NSLog(@"%@", xmlDictionary);
        
 
        NSString *jsonString = nil;
//        jsonString = jsonStringForXMLDictionary:(NSDictionary *)dictionary error:(NSError **)error
        jsonString = [XMLReader jsonStringForXMLDictionary:xmlDictionary error:&dictConvert2StringError];
        NSLog(@"%@", jsonString);
        
    }
    return 0;
}