Simple Service Client

Simple Service Client is the calling side of the Simple Service example: it wraps one SetBoolServiceClient in a Node and keeps a std_srvs/SetBool service in sync with a switch — the switch expresses the desired lamp state, and the service response reports what the server actually did.

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_service_client/CMakeLists.txt in Qt Creator, then build and run.
3. Provide the service by running the Simple Service example with the same topic.

Calling a service by binding

A service client is declared as a child of a Node. Binding the request property is all it takes to call the service: every change of the bound value schedules a call (multiple changes per event-loop iteration coalesce into one), and the result lands in the read-only response property:

import QtRos2.StdSrvs

Node {
    id: rosNode
    nodeName: "simple_service_client_node"

    SetBoolServiceClient {
        id: lampClient
        topic: topicField.text
        request: lampSwitch.checked
    }
}

Label {
    text: lampClient.response.message
}

The request binding behaves like desired state that is reconciled with the server: if the service is not available yet, or a call is still in flight, the latest value is remembered and dispatched as soon as possible. Flip the switch before starting the server and the state is applied the moment the server appears. This behavior is controlled by autoCall (on by default; auto-calls only happen when request is actually written).

Run it against Simple Service and burn the bulb out: the response switches to success: false with an explanatory message — service failure is in-band, part of the response value, so it is bindable state like everything else.

Imperative calls

callService() remains for one-shot, imperative calls; it returns a JavaScript promise:

lampClient.callService(true).then(response => {
    console.log(response.success, response.message)
}, error => {
    console.log("call failed:", error)
})

Either way, isServiceReady reports whether a server was discovered on the graph, isCallPending is true while a response is awaited, and transport-level failures (the server disappearing mid-call) are reported through the callFailed signal and the promise rejection.

Files:

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

Images:

• simple_service_client/simple_service_client.png