ios - 回调中的 Swift UI 更新有时不执行

Question

当执行下面的代码时，我看到回调执行(通过“成功!”验证)，但 UI activityIndi​​cator 上的 activityIndi​​cator 不会停止旋转。

有时它会在 10-20 秒后停止，有时它会一直运行。回调应该在主线程上运行，所以我不确定是什么导致它延迟/失败。

activityIndicator.startAnimating()
loadData("data") {(success: Bool) in
    if success {
        // I see this being printed
        println("success!")
    }

    // This isn't updating on the UI! The wheel keeps spinning
    self.activityIndicator.stopAnimating()
}

loadData 函数正在使用 Core Data 执行 block 保存:

public func loadData(completionHandler: (success: Bool) -> Void) {
    let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
    let appContext = appDelegate.managedObjectContext!
    let managedContext = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
    managedContext.persistentStoreCoordinator = appContext.persistentStoreCoordinator

    managedContext.performBlock({

        //NSManagedObject inserts - working...

        if !managedContext.save(&error) {
            completionHandler(success: false)
        }
    completionHandler(success: true)
    })
}

非常感谢这里的任何帮助!

Answer 1

    activityIndicator.startAnimating()
loadData("data") {(success: Bool) in
    if success {
        // I see this being printed
        println("success!")
    }

    dispatch_async(dispatch_get_main_queue()) {
    // This isn't updating on the UI! The wheel keeps spinning
    self.activityIndicator.stopAnimating()
    }
}

我还注意到，如果出现错误，您将调用完成 block 两次。因此，在第一个完成 block 之后添加一个返回。像这样:

public func loadData(completionHandler: (success: Bool) -> Void) {
let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let appContext = appDelegate.managedObjectContext!
let managedContext = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)
managedContext.persistentStoreCoordinator = appContext.persistentStoreCoordinator

managedContext.performBlock({

    //NSManagedObject inserts - working...

    if !managedContext.save(&error) {
        completionHandler(success: false)
        return
    }
completionHandler(success: true)
})