ios - 为什么 label.text 更新没有反射(reflect)在屏幕上？

Question

我有一个简单的测试应用程序，它向 NSOperationQueue 提交一些作业，然后等待它们完成。然后我有一个例程来检查队列中的作业数量，并应该更新屏幕上的值。同时它将值打印到控制台。控制台的工作方式完全符合我的预期，每十秒打印一个数字。数字减少到零，警报被触发。但标签(进度)在任何阶段都不会从“你好”改变。

我有一种感觉，与其说它是我代码中的错误，不如说它是我对 Swift 的理解中的一个大漏洞。请帮忙。

我的代码:

Import UIKit

class TestUpload: UIViewController {


@IBOutlet weak var progress: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    progress.text = "Hello"

    // submit some jobs ….        
    // * I have omitted this code as I don't think it has a problem. * //

    let time = dispatch_time(dispatch_time_t(DISPATCH_TIME_NOW), 10 * Int64(NSEC_PER_SEC))
    dispatch_after(time, dispatch_get_main_queue()) {

        self.showProgress()
    }

}

func showProgress() {

    while Int(session.operationQueue.operationCount) > 0 {
        sleep(10)
        print(session.operationQueue.operationCount)
        progress.text = String(session.operationQueue.operationCount)
    }

    let confirmUpload = UIAlertController(title: "Your Tasks have been performed.", message: "Congratulation!", preferredStyle: UIAlertControllerStyle.Alert)
    confirmUpload.addAction(UIAlertAction(title: "Ok", style: .Default, handler: { (action: UIAlertAction!) in  self.navigationController?.popViewControllerAnimated(true)}))

    presentViewController(confirmUpload, animated: true, completion: nil)


}

Answer 1

在 showProgress 方法结束之前，UI 不会更新。因此，如果您想要的话，您可以执行类似下面的操作。

作为不同的线程调用，

NSThread.detachNewThreadSelector("showProgress", toTarget: self, withObject: nil)

然后在主线程上更新UI

func showProgress() {

    while Int(session.operationQueue.operationCount) > 0 {
        sleep(10)
        print(session.operationQueue.operationCount)

        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            progress.text = String(session.operationQueue.operationCount)
        })
    }

    dispatch_async(dispatch_get_main_queue(), { () -> Void in
    let confirmUpload = UIAlertController(title: "Your Tasks have been performed.”, message: “Congratulation!”, preferredStyle: UIAlertControllerStyle.Alert)
        confirmUpload.addAction(UIAlertAction(title: "Ok", style: .Default, handler: { (action: UIAlertAction!) in  self.navigationController?.popViewControllerAnimated(true)}))

        presentViewController(confirmUpload, animated: true, completion: nil)
    })


}

在主线程中同时运行不会解决您的问题，即使您将其设为异步调度也是如此