现在开发大多数时候都是通过json数据进行服务器与客户端的数据传输，但有时候也会遇到利用XML字符串进行交互的情况，本文将对这一功能进行基础讲解。

1.准备

• 下载第三方库，将GDataXMLNode导入到工程里。
• 在Xcode－－>Build Phases－－>Link Binary With Libraries里面添加libxml2.tbd
• 在Xcode－－>Build Phases－－>Complie Sources里面找到GDataXMLNode.m，双击Complier Flag区域，添加-fno-objc-arc字段
• 在Xcode－－>Build Settings－－>Header Search Paths里面添加/usr/include/libxml2项。
• 在Xcode－－>Build Settings－－>Other Linker Flags里面添加-lxml2项。

2.实现

• 拼接XML文件

//这是关于DLNA功能的DIDL-Lite标准字段值
-(void)appendXMLString
{
    //添加根节点
    GDataXMLElement * rootElement = [GDataXMLNode elementWithName:@"DIDL-Lite"];
    //根节点到属性及值
    GDataXMLElement * rootFirstArg = [GDataXMLNode attributeWithName:@"xmlns" stringValue:@"urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/"];
    GDataXMLElement * rootSecondArg = [GDataXMLNode attributeWithName:@"xmlns:dc" stringValue:@"http://purl.org/dc/elements/1.1/"];
    GDataXMLElement * rootThirdArg = [GDataXMLNode attributeWithName:@"xmlns:upnp" stringValue:@"urn:schemas-upnp-org:metadata-1-0/upnp/"];
    GDataXMLElement * rootFourthArg = [GDataXMLNode attributeWithName:@"xmlns:dlna" stringValue:@"urn:schemas-dlna-org:metadata-1-0/"];
    [rootElement addAttribute:rootFirstArg];
    [rootElement addAttribute:rootSecondArg];
    [rootElement addAttribute:rootThirdArg];
    [rootElement addAttribute:rootFourthArg];
    
    //添加item节点
    GDataXMLElement * itemElement = [GDataXMLNode elementWithName:@"item"];
    //添加item节点的属性及值
    GDataXMLElement * itemFirstArg = [GDataXMLNode attributeWithName:@"id" stringValue:@""];
    GDataXMLElement * itemSecondArg = [GDataXMLNode attributeWithName:@"parentID" stringValue:@"-1"];
    GDataXMLElement * itemThirdArg = [GDataXMLNode attributeWithName:@"restricted" stringValue:@"1"];//1 or ture
    [itemElement addAttribute:itemFirstArg];
    [itemElement addAttribute:itemSecondArg];
    [itemElement addAttribute:itemThirdArg];
    
    //添加title节点
    GDataXMLElement * titleElement = [GDataXMLNode elementWithName:@"dc:title"];
    //设置title的值
    [titleElement setStringValue:@"测试音频"];
    
    //添加res节点，属性和值
    GDataXMLElement * resElement = [GDataXMLNode elementWithName:@"res"];
    GDataXMLElement * resFisrtArg = [GDataXMLNode attributeWithName:@"duration" stringValue:@"04:48"];
    GDataXMLElement * resSecondArg = [GDataXMLNode attributeWithName:@"protocolInfo" stringValue:@"http-get:*::*"];
    [resElement setStringValue:@"www.baidu.com"];
    GDataXMLElement * upnpClassEle = [GDataXMLNode elementWithName:@"upnp:class"];
    [upnpClassEle setStringValue:@"object.item.audioItem.musicTrack"];
    
    //一层一层的往上加节点，构成xml结构
    [resElement addAttribute:resFisrtArg];
    [resElement addAttribute:resSecondArg];
    
    [itemElement addChild:titleElement];
    [itemElement addChild:resElement];
    [itemElement addChild:upnpClassEle];
    
    [rootElement addChild:itemElement];
    
    NSString * rootStr = [rootElement XMLString];
    NSLog(@"%@",rootStr);
    
    GDataXMLDocument * doc = [[GDataXMLDocument alloc] initWithRootElement:rootElement];
    [doc setVersion:@"1.0"];
    [doc setCharacterEncoding:@"utf-8"];
    NSString * docStr = [[NSString alloc] initWithData:doc.XMLData encoding:NSUTF8StringEncoding];
    [self saveXMLToDocDir:docStr];
}
-(void)saveXMLToDocDir:(NSString *)doc
{
    NSString * xml = [DOCDIR stringByAppendingPathComponent:@"test.xml"];
    [[NSFileManager defaultManager] createFileAtPath:xml contents:[doc dataUsingEncoding:NSUTF8StringEncoding] attributes:nil];
   
    NSLog(@"沙盒路径：%@",xml);
}

• 解析XML文件

-(NSString *)getXMLFile
{
    NSString * filePath = [DOCDIR stringByAppendingPathComponent:@"test.xml"];
    NSString * file = [NSString stringWithContentsOfFile:filePath encoding:NSUTF8StringEncoding error:nil];
    return file;
}
-(void)praseXMLStringWithFile
{
    NSString * file = [self getXMLFile];
    GDataXMLDocument * doc = [[GDataXMLDocument alloc] initWithXMLString:file options:0 error:nil];
    //获取根节点
    GDataXMLElement * rootElement = [doc rootElement];
    NSLog(@"根节点的标签是：%@",[rootElement name]);
    
    //获取所有item节点
    NSArray * itemElementArray = [rootElement elementsForName:@"item"];
    
    for (int i=0; i<itemElementArray.count; i++) {
        GDataXMLElement * itemElment = itemElementArray[i];
        //获取属性为parentID的值
        NSString * itemFirstArg = [[itemElment attributeForName:@"parentID"] stringValue];
        NSLog(@"itemFirstArg:%@",itemFirstArg);
        
        //获取所有title节点
        NSArray * dcTitleArray = [itemElment elementsForName:@"dc:title"];
        for (int j=0; j<dcTitleArray.count; j++) {
            GDataXMLElement * titleElement = dcTitleArray[j];
            //获取title节点的值
            NSString * title = [titleElement stringValue];
            NSLog(@"title:%@",title);
        }
    }
}

完成。
附上DEMO。
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