Question

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

有时它会在10-20秒后停止，有时会永远运行。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()
    }
}

此外，我注意到如果出现错误，您将调用完成块两次。所以在第一个完成块之后添加一个返回。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)
})

}

Answer 2

我有一个类似的问题并通过首先设置活动指示器的动画，然后将剩下的代码放到后台线程，然后在主线程上调用stop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()
})
}

我没有在这里更新结束括号，假设你有更多因为你正在工作的闭包。

回调中的Swift UI更新有时不会执行

2 个答案: