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
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];
其他回答
斯威夫特 4+
解决方案我使用多年没有任何问题。首先，我扩展UIWindow来找到它的visibleViewController。注意:如果您使用自定义集合*类(如侧菜单)，您应该在以下扩展中为这种情况添加处理程序。在获得top most视图控制器后，很容易呈现UIAlertController，就像UIAlertView一样。
extension UIAlertController {
func show(animated: Bool = true, completion: (() -> Void)? = nil) {
if let visibleViewController = UIApplication.shared.keyWindow?.visibleViewController {
visibleViewController.present(self, animated: animated, completion: completion)
}
}
}
extension UIWindow {
var visibleViewController: UIViewController? {
guard let rootViewController = rootViewController else {
return nil
}
return visibleViewController(for: rootViewController)
}
private func visibleViewController(for controller: UIViewController) -> UIViewController {
var nextOnStackViewController: UIViewController? = nil
if let presented = controller.presentedViewController {
nextOnStackViewController = presented
} else if let navigationController = controller as? UINavigationController,
let visible = navigationController.visibleViewController {
nextOnStackViewController = visible
} else if let tabBarController = controller as? UITabBarController,
let visible = (tabBarController.selectedViewController ??
tabBarController.presentedViewController) {
nextOnStackViewController = visible
}
if let nextOnStackViewController = nextOnStackViewController {
return visibleViewController(for: nextOnStackViewController)
} else {
return controller
}
}
}
在Swift 3中
let alertLogin = UIAlertController.init(title: "Your Title", message:"Your message", preferredStyle: .alert)
alertLogin.addAction(UIAlertAction(title: "Done", style:.default, handler: { (AlertAction) in
}))
self.window?.rootViewController?.present(alertLogin, animated: true, completion: nil)
你可以使用两种方法:
-使用UIAlertView或'UIActionSheet'代替(不推荐，因为它在iOS 8中已弃用，但现在可以使用了)
-记得上次显示的视图控制器。举个例子。
@interface UIViewController (TopController)
+ (UIViewController *)topViewController;
@end
// implementation
#import "UIViewController+TopController.h"
#import <objc/runtime.h>
static __weak UIViewController *_topViewController = nil;
@implementation UIViewController (TopController)
+ (UIViewController *)topViewController {
UIViewController *vc = _topViewController;
while (vc.parentViewController) {
vc = vc.parentViewController;
}
return vc;
}
+ (void)load {
[super load];
[self swizzleSelector:@selector(viewDidAppear:) withSelector:@selector(myViewDidAppear:)];
[self swizzleSelector:@selector(viewWillDisappear:) withSelector:@selector(myViewWillDisappear:)];
}
- (void)myViewDidAppear:(BOOL)animated {
if (_topViewController == nil) {
_topViewController = self;
}
[self myViewDidAppear:animated];
}
- (void)myViewWillDisappear:(BOOL)animated {
if (_topViewController == self) {
_topViewController = nil;
}
[self myViewWillDisappear:animated];
}
+ (void)swizzleSelector:(SEL)sel1 withSelector:(SEL)sel2
{
Class class = [self class];
Method originalMethod = class_getInstanceMethod(class, sel1);
Method swizzledMethod = class_getInstanceMethod(class, sel2);
BOOL didAddMethod = class_addMethod(class,
sel1,
method_getImplementation(swizzledMethod),
method_getTypeEncoding(swizzledMethod));
if (didAddMethod) {
class_replaceMethod(class,
sel2,
method_getImplementation(originalMethod),
method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
}
@end
用法:
[[UIViewController topViewController] presentViewController:alertController ...];
在调用类方法之前注册通知。
斯威夫特代码:
NSNotificationCenter.defaultCenter().addObserver(self, selector: "displayAlert", name: "ErrorOccured", object: nil)
在displayAlert实例方法中，您可以显示警报。
在Objective-C中显示警报的简单方法:
[[[[UIApplication sharedApplication] keyWindow] rootViewController] presentViewController:alertController animated:YES completion:nil];
alertController是你的UIAlertController对象。
注意:你还需要确保你的助手类扩展了UIViewController
