xcode - 使用 GData 库更新节点

Question

嗨，我正在使用 Gdata 库，我被困在一个地方，我想从 xml 节点更新特定数据。下面给出的是我正在尝试更新的代码

-(void)UpdateTheXMLNode
{
    NSArray *docdirpath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *fileLoc = [[docdirpath objectAtIndex:0] stringByAppendingPathComponent:@"SomeXML.xml"];

    NSData *xmlData = [NSData dataWithContentsOfFile:fileLoc];
    GDataXMLDocument *doc = [[GDataXMLDocument alloc]initWithData:xmlData options:0 error:nil];
    NSArray *a = [doc.rootElement elementsForName:@"row"];
    NSLog(@"data before = %@",[[[a objectAtIndex:0] childAtIndex:1]stringValue]);
   [[[a objectAtIndex:0] childAtIndex:1]setStringValue:@"Yahooo"];

    [a writeToFile:fileLoc atomically:YES];
     NSLog(@"data after = %@",[[[a objectAtIndex:0] childAtIndex:1]stringValue]);

}

但是，唉，它现在给了我任何结果，所以请帮帮我。