如何在 NSOperation 中执行异步 NSURLConnection？

Question

我想在后台线程上的 NSOperation 内部执行异步 NSURLConnection 。

（这是因为我正在对数据进行一些非常昂贵的操作，因为它们返回时希望在数据进入和在后台时完成）

这是我的第一次尝试：

在我的AppDelegate中：

// create the opperation and add it to the queue:
self.sharedOperationQueue = [[[NSOperationQueue alloc] init] autorelease];
LibXMLOperation *op = [[[LibXMLOperation alloc] init] autorelease];
[self.sharedOperationQueue addOperation:op];

这是我的操作：

@interface EbirdLibXMLOperation : NSOperation {
@private
  NSURLConnection *urlConnection;
 // Overall state of the parser, used to exit the run loop.
 BOOL done;
 // properties to maintain the NSOperation
 BOOL finished;
 BOOL executing;  
}
- (void)downloadAndParse:(NSURL *)url;
- (void)start;
- (BOOL)isConcurrent;
- (BOOL)isFinished;
- (BOOL)isExecuting;

@property BOOL done;
@property (nonatomic, retain) NSURLConnection *ebirdConnection;
// The autorelease pool property is assign because autorelease pools cannot be retained.
@property (nonatomic, assign) NSAutoreleasePool *downloadAndParsePool;

@end


@implementation LibXMLOperation
@synthesize urlConnection, done;

- (void)start{
  if (![self isCancelled]) {
    [self willChangeValueForKey:@"isExecuting"];
    executing = YES;
    //set up the thread and kick it off...
    [[NSURLCache sharedURLCache] removeAllCachedResponses];
    NSURL *url = [NSURL URLWithString:@"http://google.com"];
    [NSThread detachNewThreadSelector:@selector(downloadAndParse:) toTarget:self withObject:url];
    [self didChangeValueForKey:@"isExecuting"];
  } else {
    // If it's already been cancelled, mark the operation as finished.
    [self willChangeValueForKey:@"isFinished"];
    finished = YES;
    [self didChangeValueForKey:@"isFinished"];
  }
}

- (BOOL)isConcurrent {
  return YES;
}

- (BOOL)isExecuting {
  return executing;
}

- (BOOL)isFinished {
  return finished;
}


- (void)downloadAndParse:(NSURL *)url {
  self.downloadAndParsePool = [[NSAutoreleasePool alloc] init];
  done = NO;
  self.characterBuffer = [NSMutableData data];
  [[NSURLCache sharedURLCache] removeAllCachedResponses];
  NSURLRequest *theRequest = [NSURLRequest requestWithURL:url];
  urlConnection = [[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
  if (urlConnection != nil) {
    do {
      [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    } while (!done);
  }
  [self willChangeValueForKey:@"isFinished"];
  [self willChangeValueForKey:@"isExecuting"];
  finished = YES;
  executing = NO;
  // Clean up.
  self.urlConnection = nil;
  [downloadAndParsePool release];
  NSLog(@"download and parse cleaning up");
  self.downloadAndParsePool = nil;
  [self didChangeValueForKey:@"isExecuting"];
  [self didChangeValueForKey:@"isFinished"];  
}


#pragma mark NSURLConnection Delegate methods

// Disable caching so that each time we run this app we are starting with a clean slate.

- (NSCachedURLResponse *)connection:(NSURLConnection *)connection willCacheResponse:(NSCachedURLResponse *)cachedResponse {
  return nil;
}

// Forward errors to the delegate.
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {
  done = YES;
}

// Called when a chunk of data has been downloaded.
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {
  // Process the downloaded chunk of data.
  NSLog(@"Did received %i bytes", [data length]);
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
  // Set the condition which ends the run loop.
  done = YES; 
}    

@end

当这个运行时，我在日志中看到以下消息：

2009-08-20 15:18:48.858 App[1001:3e03]*** _NSAutoreleaseNoPool(): Object 0x1126a20 of class NSCFArray autoreleased with no pool in place - just leaking
Stack: (0x305a2e6f 0x30504682 0x3057deba 0x305ced09 0x30577ddf 0x3056b43e 0x3050764a 0x58fc3 0x3050a79d 0x3050a338 0x94568155 0x94568012)

此事件发生在最后 [self didChangeValueForKey:@"isFinished"];这表明我设置的 NSOperation 是错误的。

Answer 1

将以下行移动

[downloadAndParsePool release];
self.downloadAndParsePool = nil;

到 -downloadAndParse: 方法的末尾。