swift - 等到异步 api 调用完成 - Swift/IOS

Question

我正在开发一个 ios 应用程序，在我的 appDelegate 中我有:

func application(application: UIApplication!, didFinishLaunchingWithOptions launchOptions: NSDictionary!) -> Bool {    
    self.api.signInWithToken(emailstring, token: authtokenstring) {
        (object: AnyObject?, error:String?) in            
            if(object != nil){
                self.user = object as? User
                // go straight to the home view if auth succeeded
                var rootViewController = self.window!.rootViewController as UINavigationController
                let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
                var homeViewController = mainStoryboard.instantiateViewControllerWithIdentifier("HomeViewController") as HomeViewControllerenter
                // code here
                rootViewController.pushViewController(homeViewController, animated: true)
            }
        }
    return true
}

api.signInWithToken 是使用 Alamofire 进行的异步调用，我想等待它完成，然后在 func 应用程序结束时返回 true。

Answer 1

Note: You should not do it this way, as it blocks the thread. See Nate's comment above for a better way.

有一种方法可以使用 GCD 等待异步调用完成。代码如下所示

var semaphore = dispatch_semaphore_create(0)

performSomeAsyncTask {
    ...
    dispatch_semaphore_signal(semaphore)
}

dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)
dispatch_release(semaphore)

维基百科有一个 OK article如果您对信号量一无所知。