NSInvocationOperation忽略maxConcurrentOperationCount

Question

我正在尝试使用NSInvocationOperation排队一些TWRequest调用。它似乎以正确的顺序添加方法调用，但doSomething：方法几乎同时被调用，即同时运行，而不是一个接一个地运行，这是我想要实现的。

此外，完整的顺序错误，这表明它没有一个接一个地运行......

- (void)prepare {

    if(!self.queue){
        self.queue = [[NSOperationQueue alloc] init];
        [self.queue setMaxConcurrentOperationCount:1];
    }

    for(NSString *text in calls){

        NSLog(@"Adding to Queue... %@", text);
        NSInvocationOperation *indexOperation = [[NSInvocationOperation alloc] initWithTarget:self  
                                                                                     selector:@selector(doSomething:) object:text];
        [self.queue addOperation:indexOperation];
    }     
}

- (void)doSomething:(NSString*)someText {

    TWRequest *request = [[TWRequest alloc] initWithURL:[NSURL URLWithString:@"http://something.com"] parameters:nil requestMethod:TWRequestMethodGET];
    NSLog(@"About to Perform Request... %@", someText);
    [request performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error)
     {
         dispatch_sync(dispatch_get_main_queue(), ^{
              // works fine
              NSLog(@"Network Finished... %@", someText);
         });
     }];
}

在日志中我看到了：

2011-12-30 18:34:34.553 app[32745:10703] Adding to Queue... 1
2011-12-30 18:34:34.555 app[32745:10703] Adding to Queue... 2
2011-12-30 18:34:34.556 app[32745:10703] Adding to Queue... 3
2011-12-30 18:34:34.557 app[32745:13e03] About to Perform Request... 1
2011-12-30 18:34:34.560 app[32745:13e03] About to Perform Request... 2
2011-12-30 18:34:34.563 app[32745:13e03] About to Perform Request... 3
2011-12-30 18:34:35.303 app[32745:10703] Network finished... 3
2011-12-30 18:34:35.454 app[32745:10703] Network finished... 2
2011-12-30 18:34:35.601 app[32745:10703] Network finished... 1

我希望在（1）完成之后看到（2）执行请求等...任何指针？

Answer 1

操作队列工作正常。正如@Joe在评论中所说，performRequestWithHandler:启动异步连接并立即返回。您可以通过在NSLog的末尾添加doSomething来查看此内容，如下所示：

- (void)doSomething:(NSString*)someText {
    TWRequest *request = [[TWRequest alloc] initWithURL:[NSURL URLWithString:@"http://something.com"] parameters:nil requestMethod:TWRequestMethodGET];
    NSLog(@"About to Perform Request... %@", someText);
    [request performRequestWithHandler:^(NSData *responseData, NSHTTPURLResponse *urlResponse, NSError *error)
     {
         dispatch_sync(dispatch_get_main_queue(), ^{
              // works fine
              NSLog(@"Network Finished... %@", someText);
         });
     }];
    NSLog(@"doSomething Finished");
}

要使每个请求按顺序发生，您需要在操作中使请求同步（使用signedRequest方法和同步NSURLConnection）或不使用操作队列并在完成时调用下一个请求当前请求的处理程序。请记住，如果使用操作队列，则执行操作的顺序不是基于它们的添加顺序。您可以考虑直接使用GCD串行调度队列。