等待一个块完成 [英] Waiting for a block to finish

问题描述

我有一个UITableView，我正在尝试获取行数。但是，我在使用块时遇到了麻烦。在下面的代码中，我只想返回count，但是我现在理解块是异步的。我环顾四周试图找到一个解决方案，但没有一个工作。我试过的一个解决方案是：我该怎么做等待一个异步调度的块完成？但是当我点击按钮转到带有表格的视图时，它只是在点击按钮时冻结。我尝试了其他一些，但它们也没有用。

I have a UITableView and I'm attempting to get the number of rows. However, I'm having trouble using blocks. In the code below I'd just like to return count, but as I now understand blocks are asynchronous. I've looked around trying to find a solution but none of them worked. One solution I tried was this: How do I wait for an asynchronously dispatched block to finish? but when I clicked on the button to go to the view with the table, it just froze when the button was clicked. I tried some others, but they also did not work.

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
  GlobalVars *globals = [GlobalVars sharedInstance];

  __block int count = 0;
  GKLocalPlayer *localPlayer = [[GameCenterHelper sharedInstance] getLocalPlayer];
  [[GameCenterHelper sharedInstance] getMatches:^(NSArray *matches) {
    NSLog(@"Matches: %@", matches);
    for (GKTurnBasedMatch *match in matches) {
      for (GKTurnBasedParticipant *participant in match.participants) {
        if ([participant.playerID isEqualToString:localPlayer.playerID]) {
          if (participant.status == GKTurnBasedParticipantStatusInvited) {
            [globals.matchesReceived addObject:match];
            count++;
            NSLog(@"INVITED");
          }
        }
      }
    }
  }];

  return count;
}

有人可以帮我正确获取数退回了吗？

Could someone help me properly get count returned?

推荐答案

您应该使用回调块。不要试图让异步代码同步运行。

You should be using callback blocks. Don't try to make asynchronous code behave synchronously.

此外，没有必要让你的GlobalVars单例保持在匹配数组上。它可能被认为是糟糕的设计。

Also, there's no need to have your GlobalVars singleton hold onto the array of matches. It could be considered bad design.

typedef void(^CallbackBlock)(id value);

- (void)viewDidLoad {
    [super viewDidLoad];
    //show some sort of loading "spinner" here
    [self loadMatchesWithCallback:(NSArray *matches) {
        //dismiss the loading "spinner" here
        self.matches = matches;
        [self.tableView reloadData];
    }];
}

- (void)loadMatchesWithCallback:(CallbackBlock)callback {
    GlobalVars *globals = [GlobalVars sharedInstance];
    GKLocalPlayer *localPlayer = [[GameCenterHelper sharedInstance] getLocalPlayer];
    [[GameCenterHelper sharedInstance] getMatches:^(NSArray *matches) {
        NSLog(@"Matches: %@", matches);
        NSMutableArray *filteredMatches = [NSMutableArray array];
        for (GKTurnBasedMatch *match in matches) {
            for (GKTurnBasedParticipant *participant in match.participants) {
                if ([participant.playerID isEqualToString:localPlayer.playerID]) {
                    if (participant.status == GKTurnBasedParticipantStatusInvited) {
                        [filteredMatches addObject:match];
                        break; //you don't want to add multiples of the same match do you?
                    }
                }
            }
        }
        if (callback) callback(filteredMatches);
    }];
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return self.matches.count;
}

这篇关于等待一个块完成的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！