使用FacebookSDK从异步块返回值的方法 [英] Method returning value from asynchronous block with FacebookSDK

问题描述

我想要做的是Facebook iOS SDK的Facebook包装器。基本上我的想法是我的ViewController除了显示ex之外什么都不做。我的朋友将通过简单的电话获得，例如

  self.friends = [FacebookWrapper myFriends]; 
 [self.tableView reloadData]; 
  

我的包装myFriends方法应如下所示

  +（NSArray *）myFriends 
 {
 __block NSArray * friends = nil; 
 [FBSession openActiveSessionWithReadPermissions：无allowLoginUI：YES completionHandler：^（FBSession *会话，FBSessionState状态，NSError *错误）{
如果（FB_ISSESSIONOPENWITHSTATE（状态））{
 [FBRequestConnection startForMyFriendsWithCompletionHandler：^（ FBRequestConnection * connection，id data，NSError * error）{
 CFRunLoopStop（CFRunLoopGetCurrent（））; 
 if（error）{
 return; 
} 
 NSArray * friendsData =（NSArray *）[数据数据]; 
 NSMutableArray * fbFriends = [NSMutableArray array]; 
 for（friendData中的朋友数据）{
朋友*朋友= [朋友friendWithDictionary：friendData]; 
 fbFriends addObject：friend]; 
} 
 friends = [NSArray arrayWithArray：fbFriends]; 
}]; 
 CFRunLoopRun（）; 
} 
}]; 
返回朋友; 
} 
  

问题是openActiveSessionWithReadPermissions和startForMyFriendsWithCompletionHandler是异步块，所以方法之前返回这些街区完成了他们的任务。

任何帮助都会非常感激。

解决方案

我过去创建了一个类似的包装器，我的方法是在调用我的包装器方法时传递一个完成块;一旦所有异步调用都完成运行，就会触发此完成块，并且它会接收您的方法在同步方案中返回的任何数据（在您的情况下，是朋友数组）。

为了说明 - 您可以将myFriends方法重新定义为：

+（void）myFriendsWithCompletionBlock：（void（^） （NSArray *朋友））completionBlock;

然后在实现中，紧跟在 friends = [NSArray arrayWithArray： fbFriends]; 一行，你会加上这个：

  if（completionBlock！= nil）{
 completionBlock（朋友）; 
} 
  

...并删除返回最后的声明。

最后，在你的视图控制器（或任何使用该方法的对象上，你会做这样的事情：

  [FacebookWrapper myFriendsWithCompletionBlock：^（NSArray * friends）{
 //做你需要做的朋友数组
 } ;; 
  

当然，这仍然是异步的 - 但是没有办法解决，因为这就是Facebook的方式SDK是构建的（而且，公平地说，这可能是最好的方法 - 等待完成同步的请求会很糟糕！）

编辑：我注意到了如果失败，你也会从包装器方法返回;在这种情况下，你可以这样做而不是返回：

  if（completionBlock！= nil）{
 completionBlock（nil）; 
} 
  

这将导致朋友 arra y当你的完成块被调用时， nil 然后你就可以在那里看到那个错误了。

<希望这有帮助！

What I am trying to do is a Facebook wrapper for the Facebook iOS SDK. Basically the idea is that my ViewController should do nothing but showing ex. my friends that will be acquired with a simple call like

self.friends = [FacebookWrapper myFriends];
[self.tableView reloadData];

My wrapper myFriends method should look like this

+ (NSArray *)myFriends
{
   __block NSArray *friends = nil;
   [FBSession openActiveSessionWithReadPermissions:nil allowLoginUI:YES completionHandler:^(FBSession *session, FBSessionState status, NSError *error) {
    if(FB_ISSESSIONOPENWITHSTATE(status)) {
    [FBRequestConnection startForMyFriendsWithCompletionHandler:^(FBRequestConnection *connection, id data, NSError *error) {
       CFRunLoopStop(CFRunLoopGetCurrent());
        if(error) {
            return;
        }
        NSArray *friendsData = (NSArray *)[data data];
        NSMutableArray *fbFriends = [NSMutableArray array];
        for(id friendData in friendsData) {
            Friend *friend = [Friend friendWithDictionary:friendData];
            fbFriends addObject:friend];
        }
        friends = [NSArray arrayWithArray:fbFriends];
    }];
    CFRunLoopRun();
    }
  }];
  return friends;
}

The issue is that the openActiveSessionWithReadPermissions and startForMyFriendsWithCompletionHandler are asynchronous blocks so the method returns before the blocks complete their task.

Any help would be much appreciated.

解决方案

I created a similar wrapper in the past and my approach was passing a "completion block" when calling my wrapper method; this completion block is then triggered once all the asynchronous calls are done running, and it receives whatever data your method would return in a synchronous scenario (in your case, the array of friends).

To illustrate - you could have your "myFriends" method redefined as:

+ (void)myFriendsWithCompletionBlock:(void (^)(NSArray *friends))completionBlock;

Then in the implementation, right after the friends = [NSArray arrayWithArray:fbFriends]; line, you would add this:

if (completionBlock != nil) {
    completionBlock(friends);
}

... and remove the return statement at the end.

Finally, on your view controller (or any object using the method, you would do something like this:

[FacebookWrapper myFriendsWithCompletionBlock:^(NSArray *friends){
    // do what you need to do with the friends array
}];

Of course, this is still asynchronous - but there's no way around since that's how the Facebook SDK was build (and, to be fair, this is probably the best way to do it - waiting for requests to finish synchronous would be terrible!)

Edit: I noticed you're also returning from the wrapper method in case it fails; in that situation, instead of returning you would do something like this:

if (completionBlock != nil) {
    completionBlock(nil);
}

That would cause the friends array to be nil when your completion block is called - you can then treat that error there however seems appropriate to you.

Hope this helped!

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