iOS 中的多线程和 NSNotification

Question

我在 AppDelegate.m 中写了几个这样的函数：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    debugMethod();
    self.WeiboStatusesDatabaseContext = [self createMainQueueManagedObjectContext];
    return YES;
}

- (void)setWeiboStatusesDatabaseContext:(NSManagedObjectContext *)WeiboStatusesDatabaseContext
{
    debugMethod();
    _WeiboStatusesDatabaseContext = WeiboStatusesDatabaseContext;
    NSDictionary *userInfo = self.WeiboStatusesDatabaseContext ? @{WeiboSTATUSESDatabaseAvailabilityContext : self.WeiboStatusesDatabaseContext} : nil;
    [[NSNotificationCenter defaultCenter] postNotificationName:WeiboSTATUSESDatabaseAvailabilityNotification
                                                    object:self
                                                  userInfo:userInfo];
}

我还在我的 MainPageCDTVC.m 中写了一个函数，它是一个 CoreData 表ViewController :

- (void)awakeFromNib
{
    debugMethod();
    [[NSNotificationCenter defaultCenter] addObserverForName:WeiboSTATUSESDatabaseAvailabilityNotification
                                                  object:nil
                                                   queue:nil
                                              usingBlock:^(NSNotification *note) {
                                                  self.managedObjectContext = note.userInfo[WeiboSTATUSESDatabaseAvailabilityContext];
                                                  debugLog(@"context = %@", self.managedObjectContext);
                                              }];
    debugLog(@"Context = %@", self.managedObjectContext);
}

当我将 MainPageCDTVC 设置为 Initial ViewController 和运行这个应用程序时，我从 Xcode 控制台得到了一个结果：

2015-04-02 11:37:38.650 WeiboDemo[962:48379] -[MainPageCDTVC awakeFromNib]
2015-04-02 11:37:38.665 WeiboDemo[962:48379] Context = (null)
2015-04-02 11:37:38.669 WeiboDemo[962:48379] -[AppDelegateapplication:didFinishLaunchingWithOptions:]
2015-04-02 11:37:38.673 WeiboDemo[962:48379] file:///Users/wlSong/Library/Developer/CoreSimulator/Devices/7DCCFF56-7A91-4DCC-BB20-CE33FCAE42BF/data/Containers/Data/Application/82C32B6F-A842-4BFD-A9DF-0126A7C290BC/Documents/
2015-04-02 11:37:38.691 WeiboDemo[962:48379] managedObjectContext have created.
2015-04-02 11:37:38.691 WeiboDemo[962:48379] -[AppDelegate setWeiboStatusesDatabaseContext:]
2015-04-02 11:37:38.695 WeiboDemo[962:48379] context = < NSManagedObjectContext: 0x7b84da00 >

我的问题是：

为什么最后出现"context = < NSManagedObjectContext: 0x7b84da00 >"？
-[AppDelegate application:didFinishLaunchingWithOptions:] 和 -[MainPageCDTVC awakeFromNib] 是否在同一个线程中？
如果他们是谁运行第一？

PS: 我是中国人，英语很差。见谅。

Answer 1

顺序是：

awakeFromNib
applicationWillFinishLaunching
applicationDidFinishLaunching

这里不用担心multi-threading/parallelism。如果您按照顺序操作，您将看到：

awakeFromNib => defaultCenter 观察者添加 => 打印（空）上下文
applicationDidFinishLaunching => 调用 setter => setter 发布通知 => 打印上下文

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