我有一个调度异步,我希望在屏幕上弹出4个警报。然后在显示新警报之前,每个警报都会被解雇。 (我在警报之间设置了3秒的延迟)
class ViewController: UIViewController {
var counter = 1
override func viewDidLoad() {
super.viewDidLoad()
for _ in 1...4{
DispatchQueue.main.asyncAfter(deadline: .now() + 3.0 * Double(counter) , execute: {
print("called")
self.showAlert()
})
}
}
func showAlert(){
let alert = UIAlertController(title: "sampleTitle \(counter)", message: "sampleMessage \(counter)", preferredStyle: .alert)
let action = UIAlertAction(title: "OK", style: .default, handler: nil)
alert.addAction(action)
counter += 1
if self.presentedViewController != nil {
dismiss(animated: true, completion: nil)
UIApplication.topViewController()?.present(alert, animated: true, completion: nil)
}else{
UIApplication.topViewController()?.present(alert, animated: true, completion: nil)
}
}
}
问题1:但由于某种原因,整个for loop
执行时没有任何延迟。我猜我不理解主队列是一个串行队列。
问题2:我在控制台中也得到以下日志,即使我正在解雇presentViewController。
called
called
called
called
2017-06-26 11:10:57.000 topViewAndAlertTest[3360:210226] Warning: Attempt to dismiss from view controller <topViewAndAlertTest.ViewController: 0x7fe630c03350> while a presentation or dismiss is in progress!
2017-06-26 11:10:57.001 topViewAndAlertTest[3360:210226] Warning: Attempt to present <UIAlertController: 0x7fe630c04180> on <UIAlertController: 0x7fe630f06fe0> while a presentation is in progress!
2017-06-26 11:10:57.001 topViewAndAlertTest[3360:210226] Warning: Attempt to dismiss from view controller <topViewAndAlertTest.ViewController: 0x7fe630c03350> while a presentation or dismiss is in progress!
2017-06-26 11:10:57.001 topViewAndAlertTest[3360:210226] Warning: Attempt to present <UIAlertController: 0x7fe630c06b40> on <UIAlertController: 0x7fe630f06fe0> while a presentation is in progress!
仅供参考我的topviewcontroller正在使用此answer
中的代码问题3:只有2个提醒弹出...我从未看到第3次,第4次提醒!
修改
在rmaddy的建议之后,我的错误略有改变:
called
called
called
called
2017-06-26 11:59:33.417 topViewAndAlertTest[4834:441163] Warning: Attempt to dismiss from view controller <topViewAndAlertTest.ViewController: 0x7fb596d05a30> while a presentation or dismiss is in progress!
2017-06-26 11:59:33.417 topViewAndAlertTest[4834:441163] Warning: Attempt to dismiss from view controller <topViewAndAlertTest.ViewController: 0x7fb596d05a30> while a presentation or dismiss is in progress!
我收到少2个警告。但仍然:一旦警报1出现在屏幕上,警报2就会解除警报,就是这样!没有延迟没有第3,第4警报!
答案 0 :(得分:2)
xCode 8.3.2,Swift 3.1
import UIKit
class ViewController: UIViewController {
var counter = 1
private var alertViewController: UIAlertController?
override func viewDidLoad() {
super.viewDidLoad()
DispatchQueue.global(qos: .utility).async {
for _ in 1...4 {
sleep(2)
DispatchQueue.main.async {
print("called")
self.showAlert()
}
}
}
}
private func createAlertView() -> UIAlertController {
let alertViewController = UIAlertController(title: "sampleTitle \(counter)", message: "sampleMessage \(counter)", preferredStyle: .alert)
let action = UIAlertAction(title: "OK", style: .default, handler: nil)
alertViewController.addAction(action)
return alertViewController
}
func showAlert(){
let presentAlert = {
DispatchQueue.main.async { [weak self] in
if let _self = self {
_self.alertViewController = _self.createAlertView()
UIApplication.topViewController()?.present(_self.alertViewController!, animated: true, completion: nil)
}
}
}
DispatchQueue.main.async { [weak self] in
if let alertViewController = self?.alertViewController {
alertViewController.dismiss(animated: true) {
presentAlert()
}
} else {
presentAlert()
}
self?.counter += 1
}
}
}
extension UIApplication {
class func topViewController(base: UIViewController? = (UIApplication.shared.delegate as! AppDelegate).window?.rootViewController) -> UIViewController? {
if let nav = base as? UINavigationController {
return topViewController(base: nav.visibleViewController)
}
if let tab = base as? UITabBarController {
if let selected = tab.selectedViewController {
return topViewController(base: selected)
}
}
if let presented = base?.presentedViewController {
return topViewController(base: presented)
}
return base
}
}