Simple Publisher

Simple Publisher is the smallest useful Qt ROS2 application: it wraps one PoseStampedPublisher in a Node and publishes a randomly generated geometry_msgs/PoseStamped every time you press a button. It is the natural starting point for learning how the bridge turns ROS 2 topics into QML types.

Running the example

1. Source your ROS 2 environment, then launch Qt Creator from the same shell so it can find the generated QML modules.
2. Open examples/simple_publisher/CMakeLists.txt in Qt Creator, then build and run.
3. Watch the published messages from a separate, ROS-sourced terminal:

   ros2 topic echo /simple_publisher_pose

Pair this example with Simple Subscriber to see both ends of a topic in two Qt windows.

Declaring a Node and a publisher

Everything ROS-facing lives inside a Node. A publisher is declared as a child of the node; the node owns the underlying rclcpp publisher and tears it down automatically:

import QtRos2.GeometryMsgs

Node {
    id: rosNode
    nodeName: "simple_publisher_node"

    PoseStampedPublisher {
        id: posePublisher
        topic: topicField.text
        autoStamp: autoStampSwitch.checked
    }
}

A few things worth noting:

• The topic is bound to a text field, so it can be edited live — the publisher re-advertises on the new topic when the binding changes.
• Node exposes an initialized property. The example keeps the Publish button disabled until rosNode.initialized is true, so the application never tries to publish before the ROS 2 context is ready.
• posePublisher.subscriberCount reports how many subscribers are currently connected — a convenient way to confirm the topic is wired up before you publish.

Publishing with a JavaScript object literal

Message value types are constructible from plain JavaScript objects, so you never have to build a message imperatively. Nested fields map directly to nested objects, and field names use Qt's camelCase spelling (frameId, not frame_id):

posePublisher.publish({
    header: {
        frameId: frameField.text
        // header.stamp is intentionally omitted — see below
    },
    pose: {
        position:    { x: 1.0, y: 2.0, z: 0.5 },
        orientation: { x: 0.0, y: 0.0, z: 0.0, w: 1.0 }
    }
})

Automatic timestamps

PoseStampedPublisher is a stamped publisher, which means its message carries a std_msgs/Header. When autoStamp is enabled (the default), the publisher fills header.stamp from the ROS 2 node clock at publish time — not from Qt's clock — so downstream nodes and TF see a consistent ROS time source. That is why the snippet above leaves header.stamp unset. The example exposes a switch so you can turn autoStamp off and supply your own stamp when you need to.

Files:

• simple_publisher/CMakeLists.txt
• simple_publisher/Main.qml
• simple_publisher/main.cpp

Images:

• simple_publisher/simple_publisher.png