Swift UI 回调中的更新有时不执行

Question

当执行下面的代码时，我看到回调执行（由 "success!" 验证），但是 UI activityIndicator 上的 activityIndicator 没有停止旋转。

有时会在 10-20 秒后停止，有时会运行永远停止。回调应该在主线程上运行ning，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 执行块保存：

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 error.So 在第一个完成块之后添加 return，您将调用完成块两次。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)
})

}

Answer 2

我有一个类似的问题并通过首先为 activity 指示器设置动画，然后将其余代码放到后台线程，然后在主线程上调用停止动画来解决它。

activityIndicator.startAnimating()
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), { ()->() in
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
 dispatch_async(dispatch_get_main_queue(), {
self.activityIndicator.stopAnimating()
})
}

我没有更新这里的右括号，假设你有更多，因为你正在使用闭包。

Swift UI 回调中的更新有时不执行

Swift UI update in callback is sometimes not executed

callback

ios

swift