lmxopcua/docs/Client.UI.md

Client UI

Overview

ZB.MOM.WW.OtOpcUa.Client.UI is a cross-platform Avalonia desktop application for connecting to and interacting with the LmxOpcUa OPC UA server. It targets .NET 10 and uses the shared IOpcUaClientService from Client.Shared for all OPC UA operations.

The UI provides a single-window interface for browsing the address space, reading and writing values, monitoring live subscriptions, managing alarms, and querying historical data.

Build and Run

cd src/ZB.MOM.WW.OtOpcUa.Client.UI
dotnet build
dotnet run

Technology Stack

Component	Technology
Framework	.NET 10
UI Toolkit	Avalonia 11.2
MVVM	CommunityToolkit.Mvvm
OPC UA	OPCFoundation.NetStandard.Opc.Ua.Client
Logging	Serilog
Theme	Avalonia Fluent

Window Layout

The application uses a single-window layout with five main areas:

┌─────────────────────────────────────────────────────────────┐
│ [Endpoint URL                    ] [Connect] [Disconnect]   │
│ ▸ Connection Settings                                       │
│ Redundancy: Warm  Service Level: 200  URI: urn:...          │
├──────────────┬──────────────────────────────────────────────┤
│              │ ┌─Read/Write─┬─Subscriptions─┬─Alarms─┬─History─┐│
│  Address     │ │                                              ││
│  Space       │ │                                              ││
│  Tree        │ │         (active tab content)                 ││
│  Browser     │ │                                              ││
│              │ │                                              ││
│  (lazy-load) │ └──────────────────────────────────────────────┘│
├──────────────┴──────────────────────────────────────────────┤
│ Connected to opc.tcp://... | LmxOpcUa | Session: ... | 3 subs│
└─────────────────────────────────────────────────────────────┘

Connection Panel

The top bar provides the endpoint URL, Connect, and Disconnect buttons. The Connection Settings expander reveals additional options when expanded:

Setting	Description
Endpoint URL	OPC UA server endpoint (e.g., opc.tcp://localhost:4840/LmxOpcUa)
Username / Password	Credentials for UserName token authentication
Security Mode	Transport security: None, Sign, SignAndEncrypt
Failover URLs	Comma-separated backup endpoints for redundancy failover
Session Timeout	Session timeout in seconds (1–3600, default 60)
Certificate Store Path	Path to the client certificate store (folder chooser)
Auto-accept certificates	Whether to accept untrusted server certificates

Settings Persistence

Connection settings are saved to {LocalAppData}/LmxOpcUaClient/settings.json after each successful connection and on window close. The settings are reloaded on next launch, including:

• All connection parameters
• Active subscription node IDs (restored after reconnection)
• Alarm subscription source node (restored with condition refresh)

Redundancy

When connected, the redundancy row displays the server's redundancy mode, service level, and application URI. The shared service handles automatic failover to backup endpoints if configured.

Browse Tree

The left panel shows the OPC UA address space as a lazy-loaded tree. Nodes are loaded on demand when expanded.

Context Menu

Right-click on tree nodes to access:

Action	Description
Subscribe	Subscribe to data changes on the selected node(s). For Object nodes, recursively subscribes all Variable descendants (up to 10 levels deep). Switches to the Subscriptions tab.
View History	Set the selected Variable node as the target in the History tab and switch to it. Only enabled for Variable nodes.
Monitor Alarms	Stop any active alarm subscription and subscribe to alarm events on the selected node. Switches to the Alarms tab with automatic condition refresh.

Multi-select is supported (Ctrl+Click, Shift+Click) for the Subscribe action.

Read/Write Tab

Select a node in the browse tree to auto-read its current value. The tab displays:

• Node ID
• Current value (arrays displayed as [0,1,2,3])
• Status code (e.g., 0x00000000 (Good))
• Source and server timestamps

To write a value, enter the new value and click Send. The service reads the current value first to determine the target type, then converts and writes.

Subscriptions Tab

Monitor live data changes from subscribed nodes. The tab shows a data grid with:

Column	Description
Node ID	The monitored node identifier
Value	Current value (arrays formatted as [v1,v2,...])
Status	OPC UA status code with description (e.g., 0x00000000 (Good))
Timestamp	Source timestamp in ISO 8601 format

Adding Subscriptions

• Type a node ID and click Add, or
• Right-click nodes in the browse tree and select Subscribe

Removing Subscriptions

Select one or more rows (Ctrl+Click for multi-select) and click Remove.

Writing Values

Double-click a subscription row to open a write dialog. The dialog:

1. Pre-fills the current value
2. Validates the input can parse to the target type before writing
3. Shows the write result status
4. Closes automatically on success, shows error in red on failure

Tab Header

The tab header shows the active subscription count: Subscriptions (26).

Persistence

Active subscription node IDs are saved when the application closes or disconnects, and restored on the next connection.

Alarms Tab

Monitor alarm/condition events from the server.

Subscribing

Enter an optional source node ID and click Subscribe. A condition refresh is automatically requested to display current retained alarms. Alternatively, right-click a node in the browse tree and select Monitor Alarms.

Alarm Display

The data grid shows retained alarm conditions with color-coded rows:

Severity Range	Color
Inactive	Light grey
Low (0–332)	Light blue
Medium (333–665)	Light yellow
High (666–899)	Light red
Critical (900–1000)	Red

Alarms are updated in place when the server re-sends condition state changes. Non-retained alarms are automatically removed.

Acknowledging Alarms

Right-click an active, unacknowledged alarm and select Acknowledge.... Enter an acknowledgment comment in the popup dialog. The alarm is acknowledged via the OPC UA Acknowledge method on the condition node.

Tab Header

The tab header shows active unacknowledged alarm count: Alarms (2).

Persistence

The alarm subscription source node is saved and restored on reconnection with automatic condition refresh.

History Tab

Read historical data from the Wonderware Historian.

Time Range

The date/time range picker provides:

• Text input — Type start and end times in yyyy-MM-dd HH:mm:ss format (UTC)
• Preset buttons — Quick selection: 5m (last 5 minutes), 1h (last hour), 1d (last day), 1w (last week)

All times are in UTC. Invalid input turns red on blur.

Query Options

Option	Description
Aggregate	Raw (default), Average, Minimum, Maximum, Count, Start, End
Interval (ms)	Processing interval for aggregate queries (shown only for aggregates)
Max Values	Maximum number of raw values to return (default 1000)

Results

The results grid displays:

Column	Description
Value	The historical value (arrays formatted)
Status	OPC UA status code with description
Source Timestamp	When the value was recorded
Server Timestamp	When the server processed the value

Status Bar

The bottom status bar shows:

• Connection state and endpoint URL
• Server name and session identifier
• Active subscription count

Architecture

Deferred Initialization

The OPC UA SDK is not loaded until the user clicks Connect. This keeps application startup instant. The IOpcUaClientService and all child ViewModels are created on first connection.

UI Thread Dispatch

All service event handlers (data changes, alarm events, connection state changes) are dispatched through an IUiDispatcher abstraction before updating ObservableCollections. In production this wraps Dispatcher.UIThread.Post(); in tests it runs synchronously.

ViewModels

ViewModel	Responsibility
MainWindowViewModel	Connection lifecycle, tab coordination, settings persistence
BrowseTreeViewModel	Root node loading, tree clearing
TreeNodeViewModel	Lazy-load children on expand via BrowseAsync
ReadWriteViewModel	Auto-read on selection, write with type coercion
SubscriptionsViewModel	Add/remove subscriptions, DataChanged event handling
AlarmsViewModel	Alarm subscribe/unsubscribe, event filtering, acknowledge
HistoryViewModel	Raw and aggregate history reads

Custom Controls

Control	Description
DateTimeRangePicker	UTC start/end text inputs with preset duration buttons

Testing

The UI has 102 unit tests covering ViewModel logic and headless rendering:

dotnet test tests/ZB.MOM.WW.OtOpcUa.Client.UI.Tests

Tests use:

• FakeOpcUaClientService — configurable fake implementing IOpcUaClientService
• SynchronousUiDispatcher — runs dispatch actions inline for deterministic testing
• FakeSettingsService — tracks save/load calls for settings persistence tests
• Avalonia headless rendering — screenshot capture for visual verification