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
除了给出的很好的答案(agilityvision, adib, malhal)。为了达到像以前的UIAlertViews那样的排队行为(避免警报窗口重叠)，使用这个块来观察窗口级别的可用性:
@interface UIWindow (WLWindowLevel)
+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block;
@end
@implementation UIWindow (WLWindowLevel)
+ (void)notifyWindowLevelIsAvailable:(UIWindowLevel)level withBlock:(void (^)())block {
UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;
if (keyWindow.windowLevel == level) {
// window level is occupied, listen for windows to hide
id observer;
observer = [[NSNotificationCenter defaultCenter] addObserverForName:UIWindowDidBecomeHiddenNotification object:keyWindow queue:nil usingBlock:^(NSNotification *note) {
[[NSNotificationCenter defaultCenter] removeObserver:observer];
[self notifyWindowLevelIsAvailable:level withBlock:block]; // recursive retry
}];
} else {
block(); // window level is available
}
}
@end
完整的例子:
[UIWindow notifyWindowLevelIsAvailable:UIWindowLevelAlert withBlock:^{
UIWindow *alertWindow = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
alertWindow.windowLevel = UIWindowLevelAlert;
alertWindow.rootViewController = [UIViewController new];
[alertWindow makeKeyAndVisible];
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:@"Alert" message:nil preferredStyle:UIAlertControllerStyleAlert];
[alertController addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleCancel handler:^(UIAlertAction *action) {
alertWindow.hidden = YES;
}]];
[alertWindow.rootViewController presentViewController:alertController animated:YES completion:nil];
}];
这将允许您避免警报窗口重叠。同样的方法可以用于为任意数量的窗口层分离和放入队列视图控制器。
其他回答
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。
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 ...];
似乎有效:
static UIViewController *viewControllerForView(UIView *view) {
UIResponder *responder = view;
do {
responder = [responder nextResponder];
}
while (responder && ![responder isKindOfClass:[UIViewController class]]);
return (UIViewController *)responder;
}
-(void)showActionSheet {
UIAlertController *alertController = [UIAlertController alertControllerWithTitle:nil message:nil preferredStyle:UIAlertControllerStyleActionSheet];
[alertController addAction:[UIAlertAction actionWithTitle:@"Cancel" style:UIAlertActionStyleCancel handler:nil]];
[alertController addAction:[UIAlertAction actionWithTitle:@"Do it" style:UIAlertActionStyleDefault handler:nil]];
[viewControllerForView(self) presentViewController:alertController animated:YES completion:nil];
}
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)
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
}
}
}
