AsyncStreamPatternDemo

A small iOS SwiftUI app showing how to use the AsyncStream.Continuation → AsyncStream pattern in Swift Concurrency:

• Networking: Bridge URLSession callbacks into AsyncStream using AsyncStream.Continuation.
• Location: Bridge CLLocationManagerDelegate into AsyncStream using AsyncStream.Continuation.
• NotificationCenter: Bridge notifications to an AsyncStream via AsyncStream.Continuation.
• CADisplayLink: Bridge frame ticks to an AsyncStream via AsyncStream.Continuation.
• Reachability (NWPathMonitor): Bridge network path updates to an AsyncStream.
• UIControl (UITextField): Bridge target–action editingChanged to an AsyncStream.

Screenshots

Run

• Open AsyncStreamPatternDemoApp.xcodeproj in Xcode 16+.
• Select the AsyncStreamPatternDemoApp scheme and a simulator/device, then press Cmd+R.
• When prompted, allow Location for the demo.

Notes: Networking uses https://jsonplaceholder.typicode.com/todos/1. DisplayLink runs on the main runloop. Reachability uses NWPathMonitor.

Why This Matters

This pattern is the async/await equivalent of the Combine Subject → Publisher pattern:

• Convert delegate-style APIs to AsyncStreams
• Drive SwiftUI UIs with async state using @Observable
• Decouple imperative event sources from async/await subscribers
• Modern Swift Concurrency approach without third-party frameworks

Architecture

• SwiftUI + MVVM
• Swift Concurrency (async/await + AsyncStream)
• @Observable and @MainActor for ViewModels
• No third-party dependencies

Comparison with Combine

Combine	Swift Concurrency
PassthroughSubject	AsyncStream.Continuation (stateless)
CurrentValueSubject	AsyncStream.Continuation (with stored value)
Publisher	AsyncStream
.sink { } / .assign	for await value in stream

Key Concepts

1. AsyncStream.Continuation is the bridge between imperative and async/await programming
2. Use continuation.yield() to send values into the stream
3. Use continuation.finish() to complete the stream
4. Handle cleanup with continuation.onTermination
5. Use @MainActor and @Observable for SwiftUI integration

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💡 Author: Banghua Zhao
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