ProviderEvent

IProviderEvent is observable event. IProvider class may optionally implement IObservable<IProviderEvent>.

/// <summary>Provider base event</summary>
public interface IProviderEvent
{
    /// <summary>Provider instance where event occured</summary>
    IProvider Provider { get; set; }
}

/// <summary>Previously acquired content may have been modified</summary>
public interface IProviderContentModifyingEvent : IProviderEvent { }
/// <summary>Previously acquired content may have been modified</summary>
public interface IProviderContentModifiedEvent : IProviderEvent { }

.TrySubscribeChain(observer, out subscription) tries to subscribe provider chain all the way to the root. Typically there is only one provider in a chain that can be subscribed.

// Create data source
var source = new Dictionary<string, string> { { "Key", "Value" } };
// Create cache
var provider = Providers.Func(new TryCreate<string, string>(source.TryGetValue!)).Cached();
// Create observer
IObserver<IProviderEvent> observer = new DelegateObserver<IProviderEvent>(null, null, @event => Console.WriteLine(@event));
// Subscribe provider
provider.TrySubscribeChain(observer, out IDisposable subsription);
// Get value from source through provider (gets cached)
WriteLine(provider["Key"]); // "Value"
// Modify source
source["Key"] = "New Value";
// Read again from provider that has previously cached value
WriteLine(provider["Key"]); // "Value"
// Invalidate cache, observer is notified with IProviderContentModifiedEvent.
provider.InvalidateCache(); // Observer prints "ProviderContentModifiedEvent { Provider = Avalanche.Utilities.Provider.Internal.TryCreateProvider<System.String,System.String>.Cached() }"
// Read again from provider that is invalidated.
WriteLine(provider["Key"]); // "New Value"
// Stop subscription
subsription.Dispose();

Full Example

Full example

using System;
using System.Collections.Generic;
using Avalanche.Utilities;
using Avalanche.Utilities.Provider;
using static System.Console;

class provider_event
{
    public static void Run()
    {
        {
            // <01>
            // Create data source
            var source = new Dictionary<string, string> { { "Key", "Value" } };
            // Create cache
            var provider = Providers.Func(new TryCreate<string, string>(source.TryGetValue!)).Cached();
            // Create observer
            IObserver<IProviderEvent> observer = new DelegateObserver<IProviderEvent>(null, null, @event => Console.WriteLine(@event));
            // Subscribe provider
            provider.TrySubscribeChain(observer, out IDisposable subsription);
            // Get value from source through provider (gets cached)
            WriteLine(provider["Key"]); // "Value"
            // Modify source
            source["Key"] = "New Value";
            // Read again from provider that has previously cached value
            WriteLine(provider["Key"]); // "Value"
            // Invalidate cache, observer is notified with IProviderContentModifiedEvent.
            provider.InvalidateCache(); // Observer prints "ProviderContentModifiedEvent { Provider = Avalanche.Utilities.Provider.Internal.TryCreateProvider<System.String,System.String>.Cached() }"
            // Read again from provider that is invalidated.
            WriteLine(provider["Key"]); // "New Value"
            // Stop subscription
            subsription.Dispose();
            // </01>
        }
    }
}