场景:用户点击视图控制器上的按钮。视图控制器是导航堆栈中最顶层的(很明显)。tap调用在另一个类上调用的实用程序类方法。这里发生了不好的事情我想在控件返回到视图控制器之前在那里显示一个警告。
+ (void)myUtilityMethod {
// do stuff
// something bad happened, display an alert.
}
这是可能的UIAlertView(但可能不太合适)。
在这种情况下，你如何在myUtilityMethod中呈现UIAlertController ?
当前回答
我尝试了上面提到的所有方法，但都没有成功。我在Swift 3.0中使用的方法:
extension UIAlertController {
func show() {
present(animated: true, completion: nil)
}
func present(animated: Bool, completion: (() -> Void)?) {
if var topController = UIApplication.shared.keyWindow?.rootViewController {
while let presentedViewController = topController.presentedViewController {
topController = presentedViewController
}
topController.present(self, animated: animated, completion: completion)
}
}
}
其他回答
斯威夫特
let alertController = UIAlertController(title: "title", message: "message", preferredStyle: .alert)
//...
var rootViewController = UIApplication.shared.keyWindow?.rootViewController
if let navigationController = rootViewController as? UINavigationController {
rootViewController = navigationController.viewControllers.first
}
if let tabBarController = rootViewController as? UITabBarController {
rootViewController = tabBarController.selectedViewController
}
//...
rootViewController?.present(alertController, animated: true, completion: nil)
objective - c
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Title" message:@"message" preferredStyle:UIAlertControllerStyleAlert];
//...
id rootViewController = [UIApplication sharedApplication].delegate.window.rootViewController;
if([rootViewController isKindOfClass:[UINavigationController class]])
{
rootViewController = ((UINavigationController *)rootViewController).viewControllers.firstObject;
}
if([rootViewController isKindOfClass:[UITabBarController class]])
{
rootViewController = ((UITabBarController *)rootViewController).selectedViewController;
}
//...
[rootViewController presentViewController:alertController animated:YES completion:nil];
我在我的AppDelegate类中使用了这段代码和一些个人变化
-(UIViewController*)presentingRootViewController
{
UIViewController *vc = self.window.rootViewController;
if ([vc isKindOfClass:[UINavigationController class]] ||
[vc isKindOfClass:[UITabBarController class]])
{
// filter nav controller
vc = [AppDelegate findChildThatIsNotNavController:vc];
// filter tab controller
if ([vc isKindOfClass:[UITabBarController class]]) {
UITabBarController *tbc = ((UITabBarController*)vc);
if ([tbc viewControllers].count > 0) {
vc = [tbc viewControllers][tbc.selectedIndex];
// filter nav controller again
vc = [AppDelegate findChildThatIsNotNavController:vc];
}
}
}
return vc;
}
/**
* Private helper
*/
+(UIViewController*)findChildThatIsNotNavController:(UIViewController*)vc
{
if ([vc isKindOfClass:[UINavigationController class]]) {
if (((UINavigationController *)vc).viewControllers.count > 0) {
vc = [((UINavigationController *)vc).viewControllers objectAtIndex:0];
}
}
return vc;
}
另一个选择:
var topController:UIViewController = UIApplication.shared.keyWindow!.rootViewController!
while ((topController.presentedViewController) != nil) {
topController = topController.presentedViewController!
}
topController.present(alert, animated:true, completion:nil)
你可以用Swift 2.2做以下事情:
let alertController: UIAlertController = ...
UIApplication.sharedApplication().keyWindow?.rootViewController?.presentViewController(alertController, animated: true, completion: nil)
Swift 3.0:
let alertController: UIAlertController = ...
UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true, completion: nil)
斯威夫特5
我刚刚创建了一个新窗口，并在其中添加了警报视图控制器。
查看类TopViewController:
https://gist.github.com/odnaks/3f3fd0d20f318c6276e76d0f9d7de5a7
我使用它很简单，像UIAlertController:
let alert = TopAlertController()
alert.title = "title"
alert.message = "message"
alert.addAction(UIAlertAction(title: "Ок", style: .default, handler: { _ in }))
alert.show()
