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
iOS13场景支持(当使用UIWindowScene时)
import UIKit
private var windows: [String:UIWindow] = [:]
extension UIWindowScene {
static var focused: UIWindowScene? {
return UIApplication.shared.connectedScenes
.first { $0.activationState == .foregroundActive && $0 is UIWindowScene } as? UIWindowScene
}
}
class StyledAlertController: UIAlertController {
var wid: String?
func present(animated: Bool, completion: (() -> Void)?) {
//let window = UIWindow(frame: UIScreen.main.bounds)
guard let window = UIWindowScene.focused.map(UIWindow.init(windowScene:)) else {
return
}
window.rootViewController = UIViewController()
window.windowLevel = .alert + 1
window.makeKeyAndVisible()
window.rootViewController!.present(self, animated: animated, completion: completion)
wid = UUID().uuidString
windows[wid!] = window
}
open override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
if let wid = wid {
windows[wid] = nil
}
}
}
其他回答
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 ...];
斯威夫特5
在显示消息后隐藏窗口是很重要的。
func showErrorMessage(_ message: String) {
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
let alertController = UIAlertController(title: "Error", message: message, preferredStyle: UIAlertController.Style.alert)
alertController.addAction(UIAlertAction(title: "Close", style: UIAlertAction.Style.cancel, handler: { _ in
alertWindow.isHidden = true
}))
alertWindow.windowLevel = UIWindow.Level.alert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.present(alertController, animated: true, completion: nil)
}
这在Swift中适用于普通的视图控制器，即使屏幕上有一个导航控制器:
let alert = UIAlertController(...)
let alertWindow = UIWindow(frame: UIScreen.main.bounds)
alertWindow.rootViewController = UIViewController()
alertWindow.windowLevel = UIWindowLevelAlert + 1;
alertWindow.makeKeyAndVisible()
alertWindow.rootViewController?.presentViewController(alert, animated: true, completion: nil)
几个月前我发过一个类似的问题，我想我终于解决了这个问题。如果你只是想看代码，请点击我文章底部的链接。
解决方案是使用一个额外的UIWindow。
当你想要显示你的UIAlertController:
使你的窗口成为键和可见窗口(window. makekeyandvisible ()) 只需使用一个普通的UIViewController实例作为新窗口的rootViewController。(窗口。rootViewController = UIViewController()) 在你窗口的rootViewController上显示你的UIAlertController
有几点需要注意:
你的UIWindow必须是强引用的。如果它没有被强引用，它将永远不会出现(因为它已经被释放了)。我建议使用属性，但我也成功地使用了关联对象。 为了确保窗口显示在其他所有内容之上(包括系统UIAlertControllers)，我设置了windowLevel。(窗口。windowLevel = UIWindowLevelAlert + 1)
最后，我有一个完整的实现，如果你只是想看看。
https://github.com/dbettermann/DBAlertController
