alarm-notification

name	alarm-notification
description	Handles alarm management, Prism events for alarms, and notification display in the Desktop Boilerplate WPF/Prism repository. Invoke when adding alarm features, alarm configuration, notification display, or working with alarm-related Prism events.

Alarm Notification Skill

Overview

This skill covers the alarm and notification system in Desktop Boilerplate, which uses Prism's IEventAggregator for cross-module alarm event communication, IAlarmService for alarm management, and the shell's HeaderViewModel for alarm display.

Core Components

Prism Events for Alarms

Defined in src/Vk.Dbp.Contracts/Events/:

// Alarm triggered — new alarm occurred
public class AlarmTriggeredEvent : PubSubEvent<AlarmTriggeredEventArgs> { }

// Alarm count changed — update badge/count
public class AlarmCountChangedEvent : PubSubEvent<int> { }

// Alarm status changed — acknowledged, resolved, etc.
public class AlarmStatusChangedEvent : PubSubEvent<AlarmStatusChangedEventArgs> { }

IAlarmService

Registered as singleton in DbpAccountModule.RegisterTypes:

containerRegistry.RegisterSingleton<IAlarmService, AlarmService>();

The service is lazy-resolved in HeaderViewModel because it lives in AccountModule which may not be loaded yet:

private IAlarmService _alarmService;
private IAlarmService AlarmService =>
    _alarmService ??= _container.Resolve<IAlarmService>();

HeaderViewModel — Alarm Display

HeaderViewModel subscribes to all three alarm events:

_eventAggregator.GetEvent<AlarmTriggeredEvent>().Subscribe(OnAlarmTriggered);
_eventAggregator.GetEvent<AlarmCountChangedEvent>().Subscribe(OnAlarmCountChanged);
_eventAggregator.GetEvent<AlarmStatusChangedEvent>().Subscribe(OnAlarmStatusChanged);

Event handlers use Dispatcher.Invoke for UI thread safety:

private void OnAlarmTriggered(AlarmTriggeredEventArgs args)
{
    Application.Current.Dispatcher.Invoke(() =>
    {
        // Update alarm badge, show notification
    });
}

Alarm Configuration

Alarm types and thresholds are managed through the AccountModule's alarm configuration views. Configuration is persisted in the database via IAlarmService.

Alarm Flow

Triggering an Alarm

1. Condition detected (e.g. sensor threshold exceeded)
2. IAlarmService.CreateAlarmAsync(alarmInfo)
3. Publish AlarmTriggeredEvent via IEventAggregator
4. Publish AlarmCountChangedEvent with new count
5. HeaderViewModel receives events → updates UI
6. Notification displayed to user

Acknowledging an Alarm

1. User clicks alarm in notification/list
2. IAlarmService.AcknowledgeAlarmAsync(alarmId, userId)
3. Publish AlarmStatusChangedEvent
4. HeaderViewModel updates alarm badge

Resolving an Alarm

1. Condition returns to normal or user resolves
2. IAlarmService.ResolveAlarmAsync(alarmId)
3. Publish AlarmStatusChangedEvent + AlarmCountChangedEvent
4. UI updates accordingly

Adding a New Alarm Type

1. Define the alarm type in the alarm configuration (database-backed).
2. In the detecting module, inject IAlarmService and IEventAggregator.
3. Call IAlarmService.CreateAlarmAsync() when the condition is detected.
4. Publish AlarmTriggeredEvent via IEventAggregator.
5. The shell's HeaderViewModel will automatically display the notification.

Notification Display Patterns

Badge Count in Header

private int _alarmCount;
public int AlarmCount
{
    get => _alarmCount;
    set => SetProperty(ref _alarmCount, value);
}

private void OnAlarmCountChanged(int count)
{
    Application.Current.Dispatcher.Invoke(() =>
    {
        AlarmCount = count;
    });
}

Alarm Notification Popup

Use HandyControl's Growl or notification components for transient alarm notifications:

private void OnAlarmTriggered(AlarmTriggeredEventArgs args)
{
    Application.Current.Dispatcher.Invoke(() =>
    {
        HandyControl.Controls.Growl.Warning(new GrowlInfo
        {
            Message = args.Message,
            WaitTime = 10,
            StaysOpen = false
        });
    });
}

Key Files

Component	Location
Alarm events	src/Vk.Dbp.Contracts/Events/
IAlarmService	src/Vk.Dbp.Contracts/Services/ (interface)
AlarmService	prismModules/Vk.Dbp.AccountModule/Services/ (implementation)
HeaderViewModel	src/Vk.Dbp.WpfWindow/ViewModels/HeaderViewModel.cs
HeaderView	src/Vk.Dbp.WpfWindow/Layout/HeaderView.xaml
Alarm config views	prismModules/Vk.Dbp.AccountModule/Views/
Alarm entities	src/Vk.Dbp.Infrastructure/Entities/

Common Issues

Issue: AlarmService not available at startup

Solution: IAlarmService is registered in AccountModule. Use lazy resolution via _container.Resolve<IAlarmService>() in components that may initialize before the module loads.

Issue: Alarm events not received

Solution: Ensure the event class inherits PubSubEvent<T> and is defined in Vk.Dbp.Contracts. Both publisher and subscriber must reference the same event type from Contracts.

Issue: UI not updating on alarm

Solution: Ensure event handlers use Application.Current.Dispatcher.Invoke() to marshal updates to the UI thread.

Issue: Memory leak from event subscriptions

Solution: ViewModels that subscribe to alarm events must implement IDisposable and unsubscribe in Dispose(). Use _isDisposed guard to prevent double-unsubscribe.

Testing

[Fact]
public void AlarmTriggered_PublishesEvent()
{
    var eventAggregator = new Mock<IEventAggregator>();
    var alarmEvent = new Mock<AlarmTriggeredEvent>();
    eventAggregator.Setup(e => e.GetEvent<AlarmTriggeredEvent>())
        .Returns(alarmEvent.Object);

    // Trigger alarm
    alarmEvent.Verify(e => e.Publish(It.IsAny<AlarmTriggeredEventArgs>()), Times.Once);
}