This document provides a detailed, step-by-step guide on building an iOS application integrated with ROS2 using the SwiftROS2 framework. In this guide, you will learn how to set up the project, configure ROS2 nodes, implement publishers and subscribers to exchange messages via DDS, and build a SwiftUI-based user interface for operating ROS2 functionality. In addition, this README offers an in-depth explanation of the dependency packages and how the DDS mechanism is implemented to support ROS2 communication. This guide assumes you have a basic understanding of Swift and iOS development. By the end, you will be able to create and run an iOS app that seamlessly interacts with ROS2 nodes.

The complete code can be found at https://github.com/LiaoChiawen/ROS2iOSApp

• Introduction
• Background and Key Concepts
• Step-by-Step Tutorial: Building an iOS App for ROS2
  • 1. Project Setup and Dependencies
  • 2. Creating the ROS2 Node
  • 3. Implementing Publishers and Subscribers
  • 4. Building the User Interface
  • 5. Running and Testing the App
• Detailed Explanation of Dependencies
  • swift-ros2
  • FastRTPSSwift
  • ros2msg
• Understanding the DDS Mechanism
• Usage Instructions
• Summary
• See Also
• Further Reading
• References

This tutorial explains how to build an iOS app that leverages ROS2 capabilities using the SwiftROS2 framework. In this guide you will learn to initialize a ROS2 node, set up publishers and subscribers via a DDS-based system, and construct a simple user interface with SwiftUI to operate core functionalities including initialization, message publishing, and node shutdown. The first 100 words of this introduction will be used as an excerpt on the Wiki index.

Before diving into the code, it is useful to understand these key concepts:

• ROS2 (Robot Operating System 2): A set of libraries and tools for building robot applications, which employs nodes, topics, and messaging to facilitate robust communication.
• DDS (Data Distribution Service): A middleware protocol used in ROS2 for real-time, scalable, and high-performance data exchange. It allows configuration of Quality of Service (QoS) parameters such as reliability and latency.
• Nodes: The computational executables in ROS2 that handle processing and communication.
• Publishers and Subscribers: Mechanisms for sending (publishing) and receiving (subscribing) messages across nodes.
• SwiftROS2: A simulated Swift library that provides interfaces to create ROS2 nodes, publishers, and subscribers.
• iOS Development using SwiftUI: SwiftUI is utilized for building modern, responsive user interfaces on iOS.

1. Clone the Repository:
   Begin by cloning the codebase. Your repository key directories are:

   • /ROS2iOS: Contains the main source code.
   • /ROS2iOSAppTests: Holds unit tests.
   • /Preview Content: Contains sample packages and resources.

2. Install Dependencies:
   This project uses Swift Package Manager. Open your Xcode workspace (e.g. ROS2iOS.xcodeproj) and ensure the following packages are correctly resolved:

   • swift-ros2
   • FastRTPSSwift
   • ros2msg

   Verify that your Package.resolved file lists the correct versions.

3. Configure Xcode:
   In Xcode, set the deployment target to iOS 17.0 and ensure proper code signing configurations.

The heart of the app is the ROS2 node. The CentralNode class encapsulates ROS2 functionalities including initialization and resource management.

• Initialization:
  In ContentView.swift, the initialize() function performs the following:
  • Retrieves the device IP using getWiFiIPv4Address().
  • Creates a new CentralNode instance with a domain ID and IP address.
  • Calls asynchronous initialization on the node and associated publishers.

// Example snippet from ContentView.swift:
func initialize(){
    Task {
        configViewIP = getWiFiIPv4Address() ?? "127.0.0.1"
        observableCentralNode.centralNode = CentralNode(
            domainID: 0,
            ipAddress: configViewIP
        )
        
        guard let cn = observableCentralNode.centralNode else {
            logger.error("Central Node is not ready/available. Cannot initialize.")
            return
        }
        await cn.initialize()
        await publisherModel.initialize(centralNode: cn)
    }
}

Communication between nodes is achieved by creating both publishers and subscribers.

• Publishing:
  The PublisherModel.swift file demonstrates setting up a publisher.

// Excerpt from PublisherModel.swift:
public func sendString() {
    guard let publisher = self.publisher else {
        logger.error("Publisher is not initialized.")
        return
    }
    
    let ros2str = ROS2String()
    ros2str.data = "Hello World!"
    
    let ddsMsg = DDSString(val: ros2str)
    
    Task {
        await publisher.publish(ddsMsg)
        logger.info("Published \(ros2str.data)")
    }
}

The UI is built using SwiftUI and consists of three main buttons:

• Initialize: Sets up the ROS2 node and publishers.
• Publish Message: Sends a test message.
• Destroy Node: Tears down the node and cleans up.

// Example snippet from ContentView.swift:
var body: some View {
    VStack(spacing: 20) {
        Button("Initialize") {
            initialize()
        }
        .font(.headline)
        .frame(width: 140, height: 44)
        .padding()
        .background(Color.orange)
        .foregroundColor(.white)
        .cornerRadius(8)
        
        Button("Publish Message") {
            publisherModel.sendString()
        }
        .font(.headline)
        .frame(width: 140, height: 44)
        .padding()
        .background(Color.blue)
        .foregroundColor(.white)
        .cornerRadius(8)
        
        Button("Destroy Node") {
            destroyNode()
        }
        .font(.headline)
        .frame(width: 140, height: 44)
        .padding()
        .background(Color.red)
        .foregroundColor(.white)
        .cornerRadius(8)
    }
    .padding()
}

• Build the Project:
  Use Xcode to build the project ensuring that all dependencies are properly integrated.
• Run on Simulator or Device:
  Launch the app on an iOS device or Simulator. Use the buttons to initialize the ROS2 node, publish a message, and destroy the node.
• Testing:
  Verify the functionality by checking Xcode console logs and running unit tests located in /ROS2iOSAppTests.

• Purpose:
  Provides a high-level Swift interface to interact with ROS2, allowing creation of nodes, publishers, and subscribers.
• Usage:
  Classes such as CentralNode use this package to encapsulate ROS2 operations and expose easy-to-use methods to initialize nodes and create communication channels.
• Implementation:
  Utilizes Swift’s async/await for asynchronous operations and error-handling mechanisms for reliable integration with ROS2 middleware.

• Purpose:
  Bridges ROS2 DDS functionalities by leveraging the Fast RTPS (Real-Time Publish-Subscribe) protocol.
• Usage:
  Manages low-level DDS operations such as registering writers (publishers) and readers (subscribers) and handles QoS settings (e.g., reliability, durability).
• Implementation:
  Wraps the native C/C++ Fast RTPS libraries into Swift-friendly APIs, abstracting the complexity involved in direct DDS communications.

• Purpose:
  Defines message types and data structures used in ROS2 communications.
• Usage:
  Provides message models like ROS2String to package data and ensure proper serialization and deserialization using Swift’s Codable protocol.
• Implementation:
  Structures messages in a way that aligns with ROS2 standards, facilitating seamless interaction between different nodes and platforms.

DDS (Data Distribution Service) underpins the efficient and reliable exchange of data between ROS2 nodes. Key points include:

• DDS Communication Model:
  Uses a publish/subscribe model where publishers send messages to topics and subscribers receive them based on topic subscriptions.
• Quality of Service (QoS):
  DDS allows customization of parameters (e.g., reliability, durability, latency) ensuring high-performance communication even in real-time applications.
• Fast RTPS Integration:
  The FastRTPSSwift package bridges the Fast RTPS library with SwiftROS2, managing:
  • Participant Creation: The ROS2 node (CentralNode) acts as a participant joining a DDS domain.
  • Writer and Reader Registration: Publishers (writers) and subscribers (readers) are registered with the DDS participant.
  • Message Routing: DDS middleware routes messages efficiently between registered writers and readers, applying QoS policies.
• Abstraction in SwiftROS2:
  SwiftROS2 simplifies these complex operations into easy-to-use Swift classes and methods, allowing developers to focus on application logic rather than low-level protocol details.

1. Clone and Open the Project:
   Clone the repository and open ROS2iOS.xcodeproj with Xcode.
2. Resolve Dependencies:
   Ensure that the Swift packages (swift-ros2, FastRTPSSwift, ros2msg) are downloaded and configured.
3. Build and Run:
   Build the project and run the app on the desired iOS simulator or device.
4. Interact with the App:
   • Tap Initialize to set up the ROS2 node.
   • Tap Publish Message to send a test ROS2 message.
   • Tap Destroy Node to gracefully shut down the ROS2 node.
5. Review Logs:
   Monitor the Xcode console for log messages confirming successful node initialization, message publishing, and node destruction.

This guide provided a comprehensive walkthrough for building an iOS app integrated with ROS2:

• Project setup, dependency resolution, and Xcode configuration.
• Initializing a ROS2 node with CentralNode and configuring communication via DDS.
• Implementing publishers and subscribers to exchange messages.
• Designing a user interface with SwiftUI and testing the functionality.
• Detailed insights into the core dependency packages and DDS integration research.

• ROS2 Official Documentation
• Fast RTPS Documentation
• Swift Package Manager Documentation
• SwiftUI Tutorials

• Advanced DDS configuration and Quality of Service (QoS) settings.
• Detailed tutorials on integrating C/C++ libraries with Swift.
• Comprehensive studies of ROS2 communication patterns and best practices.

1. Y. Hu, swift-ros2 – ROS2-like node that supports subscription and publication of DDS messages in ROS2 message format” GitHub Repository, https://github.com/strapsai/swift-ros2.
2. ROS Documentation, “Getting Started with ROS2,” available at https://docs.ros.org/.
3. Fast RTPS Documentation, available at https://fast-dds.docs.eprosima.com/en/latest/.
4. Apple Developer Documentation, “SwiftUI,” available at https://developer.apple.com/documentation/swiftui.