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
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
其他回答
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 ...];
extension UIApplication {
/// The top most view controller
static var topMostViewController: UIViewController? {
return UIApplication.shared.keyWindow?.rootViewController?.visibleViewController
}
}
extension UIViewController {
/// The visible view controller from a given view controller
var visibleViewController: UIViewController? {
if let navigationController = self as? UINavigationController {
return navigationController.topViewController?.visibleViewController
} else if let tabBarController = self as? UITabBarController {
return tabBarController.selectedViewController?.visibleViewController
} else if let presentedViewController = presentedViewController {
return presentedViewController.visibleViewController
} else {
return self
}
}
}
有了这个，你可以很容易地呈现你的警告，就像这样
UIApplication.topMostViewController?.present(viewController, animated: true, completion: nil)
需要注意的一件事是，如果有一个UIAlertController当前正在显示，UIApplication。topMostViewController将返回一个UIAlertController。在UIAlertController的顶部呈现有奇怪的行为，应该避免。因此，你应该手动检查!topMostViewController is UIAlertController)，或者如果self是UIAlertController，添加一个else if case返回nil
extension UIViewController {
/// The visible view controller from a given view controller
var visibleViewController: UIViewController? {
if let navigationController = self as? UINavigationController {
return navigationController.topViewController?.visibleViewController
} else if let tabBarController = self as? UITabBarController {
return tabBarController.selectedViewController?.visibleViewController
} else if let presentedViewController = presentedViewController {
return presentedViewController.visibleViewController
} else if self is UIAlertController {
return nil
} else {
return self
}
}
}
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。
下面的解决方案没有发挥作用，尽管它在所有版本中看起来都很有前途。这个解决方案正在生成WARNING。
警告:试图显示不在窗口层次结构中的视图!
https://stackoverflow.com/a/34487871/2369867 = > 这在当时看起来很有希望。但在Swift 3中没有。 所以我在Swift 3中回答这个问题，这不是模板示例。
一旦粘贴到任何函数中，这是相当完整的功能代码。
快速Swift 3自包含代码
let alertController = UIAlertController(title: "<your title>", message: "<your message>", preferredStyle: UIAlertControllerStyle.alert)
alertController.addAction(UIAlertAction(title: "Close", style: UIAlertActionStyle.cancel, handler: nil))
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alertController, animated: true, completion: nil)
这是在Swift 3中测试和工作的代码。
创建扩展像在Aviel Gross回答。这里有Objective-C扩展。
这里有头文件*.h
// UIAlertController+Showable.h
#import <UIKit/UIKit.h>
@interface UIAlertController (Showable)
- (void)show;
- (void)presentAnimated:(BOOL)animated
completion:(void (^)(void))completion;
- (void)presentFromController:(UIViewController *)viewController
animated:(BOOL)animated
completion:(void (^)(void))completion;
@end
和实现:*.m
// UIAlertController+Showable.m
#import "UIAlertController+Showable.h"
@implementation UIAlertController (Showable)
- (void)show
{
[self presentAnimated:YES completion:nil];
}
- (void)presentAnimated:(BOOL)animated
completion:(void (^)(void))completion
{
UIViewController *rootVC = [UIApplication sharedApplication].keyWindow.rootViewController;
if (rootVC != nil) {
[self presentFromController:rootVC animated:animated completion:completion];
}
}
- (void)presentFromController:(UIViewController *)viewController
animated:(BOOL)animated
completion:(void (^)(void))completion
{
if ([viewController isKindOfClass:[UINavigationController class]]) {
UIViewController *visibleVC = ((UINavigationController *)viewController).visibleViewController;
[self presentFromController:visibleVC animated:animated completion:completion];
} else if ([viewController isKindOfClass:[UITabBarController class]]) {
UIViewController *selectedVC = ((UITabBarController *)viewController).selectedViewController;
[self presentFromController:selectedVC animated:animated completion:completion];
} else {
[viewController presentViewController:self animated:animated completion:completion];
}
}
@end
你在你的实现文件中使用这个扩展，就像这样:
#import "UIAlertController+Showable.h"
UIAlertController* alert = [UIAlertController
alertControllerWithTitle:@"Title here"
message:@"Detail message here"
preferredStyle:UIAlertControllerStyleAlert];
UIAlertAction* defaultAction = [UIAlertAction
actionWithTitle:@"OK"
style:UIAlertActionStyleDefault
handler:^(UIAlertAction * action) {}];
[alert addAction:defaultAction];
// Add more actions if needed
[alert show];
