为何NotificationCenter+Rx属于RxCocoa而非RxSwift？

Great question—this is a common point of confusion since NotificationCenter lives in Foundation, not UIKit/AppKit. Let’s break this down clearly:

The Core Split Between RxSwift and RxCocoa #

First, let’s recap the fundamental roles of these two frameworks:

• RxSwift: This is the lightweight, platform-agnostic core of the reactive toolkit. It handles all the basic reactive primitives like Observable, Observer, operators, and scheduling—with no ties to Apple’s Cocoa/CocoaTouch frameworks. It’s designed to be usable even outside Apple ecosystems, though most developers use it alongside Apple platforms.
• RxCocoa: This layer bridges RxSwift to Apple’s native frameworks. Its sole job is to wrap Cocoa/CocoaTouch APIs (including parts of Foundation deeply tied to platform behavior) into reactive extensions. That includes UIKit controls, AppKit components, and yes—NotificationCenter.

Why NotificationCenter Lands in RxCocoa #

Even though NotificationCenter is part of Foundation, its most common use cases on Apple platforms are tightly coupled to Cocoa/CocoaTouch workflows:

• Listening to system notifications like UIApplication.didEnterBackgroundNotification or UIResponder.keyboardWillShowNotification
• Observing app-specific events tied to UI state changes
• Integrating with other Cocoa framework components that rely on notifications for communication

RxCocoa is home to all these platform-specific reactive bindings. Keeping NotificationCenter+Rx here keeps RxSwift clean, focused solely on core reactive logic without platform dependencies.

Fixing Your Error #

If your project only uses RxSwift and can’t add RxCocoa, you can easily implement a minimal version of this extension yourself using RxSwift’s core APIs:

import RxSwift
import Foundation

extension Reactive where Base: NotificationCenter {
    func notification(_ name: Notification.Name, object: AnyObject? = nil) -> Observable<Notification> {
        return Observable.create { observer in
            // Add the notification observer
            let observerToken = self.base.addObserver(
                forName: name,
                object: object,
                queue: nil
            ) { notification in
                observer.onNext(notification)
            }
            
            // Return a disposable to clean up the observer when done
            return Disposables.create {
                self.base.removeObserver(observerToken)
            }
        }
    }
}

Drop this extension into your codebase, and NotificationCenter.default.rx.notification() will work just like the RxCocoa version.

内容的提问来源于stack exchange，提问作者Jake Lin