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
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 ...];
Kevin Sliech提供了一个很好的解决方案。
我现在在我的主UIViewController子类中使用下面的代码。
我做的一个小改动是检查最好的表示控制器是不是一个普通的UIViewController。如果不是，那就一定是某个VC表示一个普通VC。因此，我们返回正在呈现的VC。
- (UIViewController *)bestPresentationController
{
UIViewController *bestPresentationController = [UIApplication sharedApplication].keyWindow.rootViewController;
if (![bestPresentationController isMemberOfClass:[UIViewController class]])
{
bestPresentationController = bestPresentationController.presentedViewController;
}
return bestPresentationController;
}
在我的测试中似乎一切正常。
谢谢你，凯文!
@agilityvision的回答非常好。我有在swift项目中使用的感觉，所以我想我将分享我使用swift 3.0的答案
fileprivate class MyUIAlertController: UIAlertController {
typealias Handler = () -> Void
struct AssociatedKeys {
static var alertWindowKey = "alertWindowKey"
}
dynamic var _alertWindow: UIWindow?
var alertWindow: UIWindow? {
return objc_getAssociatedObject(self, &AssociatedKeys.alertWindowKey) as? UIWindow
}
func setAlert(inWindow window: UIWindow) {
objc_setAssociatedObject(self, &AssociatedKeys.alertWindowKey, _alertWindow, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
}
func show(completion: Handler? = nil) {
show(animated: true, completion: completion)
}
func show(animated: Bool, completion: Handler? = nil) {
_alertWindow = UIWindow(frame: UIScreen.main.bounds)
_alertWindow?.rootViewController = UIViewController()
if let delegate: UIApplicationDelegate = UIApplication.shared.delegate, let window = delegate.window {
_alertWindow?.tintColor = window?.tintColor
}
let topWindow = UIApplication.shared.windows.last
_alertWindow?.windowLevel = topWindow?.windowLevel ?? 0 + 1
_alertWindow?.makeKeyAndVisible()
_alertWindow?.rootViewController?.present(self, animated: animated, completion: completion)
}
fileprivate override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
_alertWindow?.isHidden = true
_alertWindow = nil
}
}
为了改进敏捷视觉的答案，你需要创建一个带有透明根视图控制器的窗口，并从那里显示警报视图。
然而，只要在警报控制器中有一个动作，就不需要保持对窗口的引用。作为动作处理程序块的最后一步，您只需要将窗口隐藏为清理任务的一部分。通过在处理程序块中有一个对窗口的引用，这将创建一个临时的循环引用，一旦警报控制器被解除，该引用将被打破。
UIWindow* window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
window.rootViewController = [UIViewController new];
window.windowLevel = UIWindowLevelAlert + 1;
UIAlertController* alertCtrl = [UIAlertController alertControllerWithTitle:... message:... preferredStyle:UIAlertControllerStyleAlert];
[alertCtrl addAction:[UIAlertAction actionWithTitle:NSLocalizedString(@"OK",@"Generic confirm") style:UIAlertActionStyleCancel handler:^(UIAlertAction * _Nonnull action) {
... // do your stuff
// very important to hide the window afterwards.
// this also keeps a reference to the window until the action is invoked.
window.hidden = YES;
}]];
[window makeKeyAndVisible];
[window.rootViewController presentViewController:alertCtrl animated:YES completion:nil];
更新到与iOS 13场景，打破了新的UIWindow方法。斯威夫特5.1。
fileprivate var alertWindows = [UIAlertController:UIWindow]()
extension UIAlertController {
func presentInNewWindow(animated: Bool, completion: (() -> Void)?) {
let foregroundActiveScene = UIApplication.shared.connectedScenes.filter { $0.activationState == .foregroundActive }.first
guard let foregroundWindowScene = foregroundActiveScene as? UIWindowScene else { return }
let window = UIWindow(windowScene: foregroundWindowScene)
alertWindows[self] = window
window.rootViewController = UIViewController()
window.windowLevel = .alert + 1
window.makeKeyAndVisible()
window.rootViewController!.present( self, animated: animated, completion: completion)
}
open override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
alertWindows[self] = nil
}
}
