Ios 异步调用后返回可变字典

我是iOS编程新手，我正在尝试构建一个与另一台服务器通信的小应用程序，以检索XML并解析它。现在，我已经在同一个视图控制器中实现了NSXML解析器委托，我想编写一个单独的类来接受XML路径，解析它并返回有意义的数据

所以在视图控制器中我有这个

// On Foo Button Click
XMLParser* xmlParser = [[XMLParser alloc] init];
// XMLParser would be my class file which has a method to parse XML
xmlParser.readXMLFromPath(pathToXML);

在XMLParser类文件中：

- (NSMutableDictionary*) readXMLFromPath: (NSString* pathToXML) {
  NSMutableDictionary* resultSet;
  // Alloc NSXMLParser and implement its delegate methods
  // resultSet would now hold the needed Data
}

---

那么现在我应该如何将

resultSet

返回到viewController？

让XML解析器的客户端传入一个块，以便在结果准备好时执行，而不是立即返回它们。当出现问题时，您还可以让客户机在单独的errorBlock中传递

- (void)readXMLFromPathWithSuccessBlock:(void (^)(NSMutableDictionary *results))successBlock;
 {
  // Alloc NSXMLParser and implement its delegate methods
  // Save successBlock in a property
}

- (void)parserDidEndDocument:(NSXMLParser *)parser {
  // Call success block and pass results to the client
}

---

下面是NSOperation的一个子类，我使用它对NSOperationQueue执行所有xml解析：

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

@class ParseXMLOperation;

@protocol ParseXMLCallbackDelegate <NSObject>

-(void)parseOperationComplete:(ParseXMLOperation *)completedOperation;

@end

@interface ParseXMLOperation : NSOperation 
{
    GDBaseParser *xmlParserDelegate;
    NSData *dataToParse;
    id <ParseXMLCallbackDelegate> callbackDelegate;
}

@property(nonatomic,strong)GDBaseParser *xmlParserDelegate;
@property(nonatomic,strong)NSData *dataToParse;
@property(nonatomic,strong)id <ParseXMLCallbackDelegate> callbackDelegate;
-(id)initWithParser:(GDBaseParser *)inParserDelegate;
@end


@implementation ParseXMLOperation

@synthesize xmlParserDelegate, dataToParse, callbackDelegate;

-(id)initWithParser:(GDBaseParser *)inParserDelegate
{
    self = [super init];
    if( self != nil )
    {
        self.xmlParserDelegate = inParserDelegate;
    }
    return self;
}

-(void)main
{
    @autoreleasepool
    {

        NSXMLParser *parser  = [[NSXMLParser alloc] initWithData:dataToParse];
        xmlParserDelegate.currentContext = localContext;
        [parser setDelegate:xmlParserDelegate];
        [parser setShouldProcessNamespaces:NO];
        [parser setShouldReportNamespacePrefixes:NO];
        [parser setShouldResolveExternalEntities:NO];
        [parser parse];
        [self performSelectorOnMainThread:@selector(sendOperationComplete) withObject:nil waitUntilDone:NO];

    }


}


-(void)sendOperationComplete
{
    if( callbackDelegate != nil && [callbackDelegate     respondsToSelector:@selector(parseOperationComplete:)] )
    {
        [callbackDelegate parseOperationComplete:self];
    }
}

---

通常，这里的想法是向异步进程发送一个回调方法，当它完成时，它会调用该方法来更新UI或执行另一个任务，或者您应该了解的关于协议的内容

         MyParser *parserDelegate = [[MyParser alloc] init];
ParseXMLOperation *parseOperation = [[ParseXMLOperation alloc]   initWithParser:parserDelegate];
         parseOperation.dataToParse = parseData;
         parseOperation.completionBlock = ^{
             localOperation.messageHeaderDict = parserDelegate.messageHeaders;
             dispatch_async(dispatch_get_main_queue(), ^{
                 //notify your UI that you are done with your parsing
             });

         };
         [self.xmlParsingQueue addOperation:parseOperation];