从按钮动作调用时，UIActivityIndi​​catorView不显示 [英] UIActivityIndicatorView not showing up when invoked from button action

问题描述

我正在尝试通过按钮按压调用来显示一个微调器，但是我无法显示它.这是我的代码:

I'm trying to show a spinner during a possibly lengthy action invoked by a button press, but I can't get it to show up. Here's my code:

class ViewController: UIViewController {

   var actInd : UIActivityIndicatorView!
   [...]

   override func viewDidLoad() {

      super.viewDidLoad()

      self.actInd = UIActivityIndicatorView(frame: CGRectMake(0,0, 50, 50)) as UIActivityIndicatorView

      self.actInd.center = view.center
      self.actInd.hidesWhenStopped = true
      self.actInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
      self.view.addSubview(actInd)

      [...]
    }

    @IBAction func buttonPressed(sender: UIBarButtonItem) {
        self.actInd.startAnimating()
        // [...] do some work
        self.actInd.stopAnimating()
    }
}

在我看来，当从执行按下按钮的UI线程中启动时，动画没有显示(如果我仅在不停止的情况下在按钮调用中启动动画，则它在buttonPressed回调后立即开始显示完成).我试着玩dispatch_async，但没有得到任何结果.这是我尝试过的:

It looks to me like the animation doesn't get shown when started from within the UI thread executing the button pressed (if I only start the animation in the button call without stopping, it starts to display as soon as the buttonPressed callback finishes). I tried to play around with dispatch_async but didn't get anywhere. Here's what I tried:

第一:

    @IBAction func buttonPressed(sender: UIBarButtonItem) {

        dispatch_async(dispatch_get_main_queue()) {
            self.actInd.startAnimating()
        }
        shufflePlaylist()
        dispatch_async(dispatch_get_main_queue()) {
            self.actInd.stopAnimating()
        }
    }

第二:

    @IBAction func buttonPressed(sender: UIBarButtonItem) {

        dispatch_async(dispatch_get_main_queue()) {
            shufflePlaylist()
        }
    }

    func shufflePlaylist() {

        self.actInd.startAnimating()
        // [...] do the work
        self.actInd.stopAnimating()
    }

第三:

    @IBAction func buttonPressed(sender: UIBarButtonItem) {

        self.actInd.startAnimating()

        dispatch_async(dispatch_get_main_queue()) {
            shufflePlaylist()
        }
    }

    func shufflePlaylist() {

        // [...] do the work
        self.actInd.stopAnimating()
    }

在用户删除commitEditingStyle中的表视图行(这也会触发一些冗长的数据更新操作)之后，尝试显示微调器时，我遇到了同样的问题.

I run into the same problem when trying to show the spinner after the user deletes a table view row in (which also can trigger some lengthy data update operation) in commitEditingStyle.

那么在这些情况下显示活动指标的正确方法是什么?

So what's the right approach to show an activity indicator in those cases?

推荐答案

您想要的东西是:

@IBAction func buttonPressed(sender: UIBarButtonItem) {
  spinner.startAnimating()
  let dispatchPriority = DISPATCH_QUEUE_PRIORITY_DEFAULT
  dispatch_async(dispatch_get_global_queue(dispatchPriority, 0)) { 

    NSThread.sleepForTimeInterval(5.0) //your task here instead of this line

    dispatch_async(dispatch_get_main_queue(), {
      self.spinner.stopAnimating()
    })
  }
}

这将启动微调器，然后将其分派到后台线程，在其中执行任务(我假设您正在执行的任务是可以在后台线程上执行的任务-即它不涉及UI东西).任务完成后，该方法将分派回主UI线程，并停止微调器.

This starts the spinner,then dispatches to a background thread, performs a task there (I'm assuming the task you are performing is one that can be performed on a background thread - i.e it doesn't involve UI stuff). Once the task is complete, the method dispatches back to the main UI thread, and stops the spinner.

这篇关于从按钮动作调用时，UIActivityIndi​​catorView不显示的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！