HarmonyOS 5 Smart Terminals Hands-On: Building Responsive UI and State Management with Cangjie Language

In the era of HarmonyOS 5, the diversity of devices has expanded to include smartphones, smartwatches, smart screens, and IoT mini-terminals. Against this backdrop, user experience has become a critical factor in the success of applications. Developing smooth responsive interfaces and ensuring consistent system stability across dynamic states are challenges that every developer must address.

This article presents a hands-on implementation of a lightweight, elegant, and high-performance responsive UI and state management system using the Cangjie language, balancing performance experience with clear architectural design.

1. Responsive Architecture Design

Why Responsive UI?

Traditional imperative UI update methods look like this:

if (dataChanged) {
    updateUI()
}

This approach has several issues:

1. Scattered update logic prone to omissions and errors.
2. Difficulty synchronizing data state changes with UI updates.
3. Complex system maintenance and scaling.

The responsive UI model features automatic UI updates triggered by data changes, offering these advantages:

1. Clear data-driven principles make UI updates intuitive.
2. Unified update channels simplify management and maintenance.
3. Easier extension and testing.

How Cangjie Language Helps

1. Property Mechanism (prop / mut prop): Transparently encapsulates getters/setters to monitor data changes.
2. Pipeline Operator (|>) + Lambda: Builds clear data processing chains for optimized workflows.
3. Trailing Lambda: Makes control logic closer to natural language, improving code readability.
4. Lightweight Threads: Ensures UI updates do not block the main process, maintaining smooth operation.

Architecture Diagram

graph TD;
    A[Model State Change] --> B[Auto-Trigger View Update];
    B --> C[Render UI];

The core idea is to decouple Model and View for automatic change detection.

2. Building the State Management Model

Basic State Model Design

Use Algebraic Data Types (ADT) to manage application states and pattern matching (match-case) to dispatch update logic.

Define State Enum

enum UIState {
    | Loading
    | Loaded(String)
    | Error(String)
}

• Explicitly lists all valid states.
• Each state can carry relevant data (e.g., success data or error messages).

Define View Controller

class ViewController {
    mut prop currentState: UIState {
        get() {
            _state
        }
        set(newState) {
            _state = newState
            this.render(newState)
        }
    }

    private var _state: UIState = Loading

    private func render(state: UIState) {
        match(state) {
            case Loading => println("UI: Loading...")
            case Loaded(data) => println("UI: Displaying ${data}")
            case Error(msg) => println("UI: Error - ${msg}")
        }
    }
}

• currentState is a mutable property (mut prop).
• Assigning to it automatically triggers rendering logic—no manual updateUI calls needed.

Simulate State Transitions

main() {
    let controller = ViewController()

    thread.start {
        sleep(2 * Duration.Second)
        controller.currentState = Loaded("Sensor Data: 25°C")

        sleep(3 * Duration.Second)
        controller.currentState = Error("Connection lost")
    }

    while (true) {
        sleep(10 * Duration.Second)
    }
}

Output Example:

UI: Loading...
UI: Displaying Sensor Data: 25°C
UI: Error - Connection lost

Key Design Points

Technical Point	Role
Property-based listening	Transparently triggers rendering
ADT for state management	Ensures state completeness
Pattern matching	Clearly handles each state case

This model is clearer, more organized, and more scalable than traditional if-else logic.

3. Enhancing Performance and Experience

How to Ensure Smoothness During High-Frequency Updates?

1. Lightweight Thread Updates: Separate UI update triggers from data collection to avoid blocking.
2. Batch Rendering: Merge multiple state changes to reduce UI refresh frequency and improve performance.
3. Pipeline Data Processing: Use Cangjie’s pipeline operators to optimize data handling chains.

Example: Data Stream + Batching Optimization

class DataProvider {
    let updates = concurrent.Queue()

    public func push(state: UIState) {
        updates.enqueue(state)
    }

    public func listenUpdates(viewController: ViewController) {
        thread.start {
            while (true) {
                if (let state = updates.dequeue()) {
                    viewController.currentState = state!!
                }
            }
        }
    }
}

main() {
    let viewController = ViewController()
    let dataProvider = DataProvider()

    dataProvider.listenUpdates(viewController)

    thread.start {
        dataProvider.push(Loading)
        sleep(1 * Duration.Second)
        dataProvider.push(Loaded("Humidity: 45%"))
        sleep(2 * Duration.Second)
        dataProvider.push(Error("Sensor failure"))
    }

    while (true) {
        sleep(10 * Duration.Second)
    }
}

• DataProvider uses a concurrency-safe queue to collect state changes.
• An independent thread listens and pushes states to ViewController.
• The main thread remains unblocked for smooth operation.

Summary

The responsive UI and state management system built with Cangjie language has these characteristics:

Characteristic	Description
Clear data-driven 架构	State = UI; no manual update triggers
Easy to extend/maintain	Add new states via pattern matching
High-performance	Lightweight threads + batching for seamless transitions
Clean code	Lambda and pipeline operators enhance readability

This model is suitable for HarmonyOS 5 development in scenarios such as:

1. Real-time smart screen display systems
2. IoT device interaction interfaces
3. Data visualization dashboards
4. Smart terminal control panels

In the future, combining Cangjie’s Async Stream and composable UI frameworks (e.g., ArkTS patterns) could further evolve this into a true Declarative Reactive UI system.