ios - 如何在 SWIFT 中关闭没有任何操作的 UIAlertController？

Question

我在下载图像时显示一个 UIAlertController。下载完成后，我想推送一个 View Controller 。我在控制台中遇到错误，因为我没有关闭警报 Controller :

pushViewController:animated: called on <UINavigationController 0x7fb190c6ee00> while an existing transition or presentation is occurring; the navigation stack will not be updated.

在我的主视图 Controller 中，下载完成后，我推送另一个 View :

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {

    //....

    var alert = UIAlertController(title: "Alert", message: text, preferredStyle: UIAlertControllerStyle.Alert)
    self.presentViewController(alert, animated: true, completion: nil)


    dispatch_async(dispatch_get_main_queue(), {
        if let cellToUpdate = tableView.cellForRowAtIndexPath(indexPath) {
               self.performSegueWithIdentifier("postview", sender: self)

        }
   })
}

我尝试了 dismissViewControllerAnimated 但我有完全相同的错误:

dispatch_async(dispatch_get_main_queue(), {
            if let cellToUpdate = tableView.cellForRowAtIndexPath(indexPath) {
                   alert.dismissViewControllerAnimated(true, completion: nil)
                   self.performSegueWithIdentifier("postview", sender: self)

            }
       })

Answer 1

在关闭前一个 View Controller 之前，您不应该调用 performSegueWithIdentifier。要正确计时，请从完成处理程序执行:

dispatch_async(dispatch_get_main_queue(), {
    if let cellToUpdate = tableView.cellForRowAtIndexPath(indexPath) {
       alert.dismissViewControllerAnimated(true, completion: {
           self.performSegueWithIdentifier("postview", sender: self)
       })
    }
})

现在执行 segue 的调用在解雇结束之前不会开始，从而防止出现您看到的错误。