ios - NSMutable 数组在退出函数后不保留数据

Question

我有一个 tableView，我正在尝试用数据填充它。我正在为函数内的数组赋值。所有内容都会保存起来，直到它离开 searchWithLocation 函数。查看日志让我认为这与排序有关，就像我没有足够快地填充数据一样。或者也许这不是原因，我真的不知道。

- (void)viewDidLoad {
    [super viewDidLoad];

    venueName = [[NSMutableArray alloc] init];

    [YLPClient authorizeWithAppId:@"sdgsfgfgfg"
                           secret:@"aegsgdgdfs"
                completionHandler:^
     (YLPClient *client, NSError *error) {
         // Save your newly authorized client
         self.client = client;

         [self.client searchWithLocation:@"Chicago"
                       completionHandler:^
          (YLPSearch *search, NSError *error) {
              for (YLPBusiness *business in search.businesses) {
                  [venueName addObject:business.name];
              }
              NSLog(@"I return results: %lu", (unsigned long)[venueName count]);
          }];
         NSLog(@"I return 0: %lu", (unsigned long)[venueName count]);
     }];
}

...

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSLog(@"number of rows in section: %lu", (unsigned long)[venueName count]);
    return [venueName count];
}

日志:

2017-09-02 14:46:39.708 whatever[67890:8535793] number of rows in section: 0
2017-09-02 14:46:39.714 whatever[67890:8535793] number of rows in section: 0
2017-09-02 14:46:39.715 whatever[67890:8535793] number of rows in section: 0
2017-09-02 14:46:40.448 whatever[67890:8535846] I return 0: 0
2017-09-02 14:46:41.174 whatever[67890:8535846] I return results: 20

Answer 1

你对异步程序执行有误解。每个完成处理程序都可以在“调用”执行路径已经终止后执行。对于您的情况:

[self.client searchWithLocation:@"Chicago"
              completionHandler:
  // This completion handler can be executed after seconds, minutes or even hours.
  ^(YLPSearch *search, NSError *error) 
  {
    NSLog( @"As times go by – sometime in the future" );
    for (YLPBusiness *business in search.businesses) 
    {
      [venueName addObject:business.name];
    }
    NSLog(@"I return results: %lu", (unsigned long)[venueName count]);
  }];
  // This path is executed immediately. esp. likely before the cmpletion handler is executed
  NSLog( @"It is now or never" );
  NSLog(@"I return 0: %lu", (unsigned long)[venueName count]);

将完成处理程序后面的代码移到其中。