代码：
func showAlert(vc:UIViewController, title:String, message:String? = nil){
dispatchMain_async({
let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
let sureAlertAction = UIAlertAction(title: "确定", style: UIAlertActionStyle.Destructive, handler: nil)
alertController.addAction(sureAlertAction)
vc.presentViewController(alertController, animated: true, completion: nil)
})
}
当前vc，已经通过点击导航栏的返回按钮，消失了，然后调用到：
vc.presentViewController(alertController, animated: true, completion: nil)
出错：
Presenting view controllers on detached view controllers is discouraged
界面效果：
此处情况是：
调用
vc.presentViewController(alertController, animated: true, completion: nil)
时
对应的vc，已经（通过点击导航栏中的返回按钮）消失了
也的确是有问题的。
Presenting view controllers on detached view controllers is discouraged
Swift: "Presenting view controllers on detached view controllers is discouraged"
ios – Presenting view controllers on detached view controllers – Stack Overflow
ios – Presenting view controllers on detached view controllers is discourage – Stack Overflow
swift check view controller not detached
最后改为：
func showAlert(vc:UIViewController, title:String, message:String? = nil){
dispatchMain_async({
let alertController = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.Alert)
let sureAlertAction = UIAlertAction(title: "确定", style: UIAlertActionStyle.Destructive, handler: nil)
alertController.addAction(sureAlertAction)
if isCurrentShowingVc(vc) {
vc.presentViewController(alertController, animated: true, completion: nil)
}
})
}
即可。
至少目前实现了：
当前的vc不是当前页面的话，就不提示了。
－》之前的case是：
点击返回按钮，当前页面已经不在导航栏的视图堆栈中了，所以就不显示了。
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