Subjects

Lesson in the iOS Roadmap · Stage 16: Delegate Pattern

Last updated 14 September 2026

What is Subjects?

Subjects in RxSwift act as both Observables and Observers, making them useful for bridging non-reactive code into reactive streams. PublishSubject emits only new items to subscribers; BehaviorSubject replays the last value to new subscribers; and ReplaySubject replays a configurable number of past values. Subjects are commonly used as input channels in MVVM ViewModels.

Study this in the interactive course See the whole iOS roadmap

Free resources to learn Subjects

Official docsReactiveX Subject Documentation
ArticleRxSwift Subjects Reference
ArticleRxSwift Subjects

Subjects: common questions

Can I learn Subjects in Hindi?

This lesson is written in English. Once you sign in, open it in the interactive course and ask the AI tutor to explain Subjects in Hindi or Hinglish. The tutor answers from this lesson’s own text, so it stays on the syllabus, and it runs on your own Google, OpenAI or Anthropic key.

Is this Subjects tutorial for beginners?

It is lesson 98 of 170 in the free iOS roadmap, in stage 16, Delegate Pattern. If you are new to iOS, start from stage 1 and come back here in order; if you already know the earlier stages, this lesson stands on its own.