Introduce Activity Behaviors

Activity Behaviors allow for code reuse between activities. Useful for certain signal handling like Break for example.

src/core/Elsa.Core/Activities/For.cs

@@ -1,8 +1,8 @@
 using System.Text.Json.Serialization;
 using Elsa.Attributes;
+using Elsa.Behaviors;
 using Elsa.Contracts;
 using Elsa.Models;
-using Elsa.Signals;
 
 namespace Elsa.Activities;
 
@@ -20,7 +20,7 @@ public class For : Activity
     [JsonConstructor]
     public For()
     {
-        OnSignalReceived<BreakSignal>(OnBreakAsync);
+        Behaviors.Add<BreakBehavior>();
     }
 
     public For(int start, int end, ForOperator forOperator = ForOperator.LessThanOrEqual) : this()
@@ -85,16 +85,4 @@ public class For : Activity
         HandleIteration(ownerActivityExecutionContext);
         return ValueTask.CompletedTask;
     }
-    
-    private async ValueTask OnBreakAsync(BreakSignal signal, SignalContext context)
-    {
-        // Prevent bubbling.
-        context.StopPropagation();
-
-        // Remove child activity execution contexts.
-        context.ActivityExecutionContext.RemoveChildren();
-
-        // Mark this activity as completed.
-        await context.ActivityExecutionContext.CompleteActivityAsync();
-    }
 }

src/core/Elsa.Core/Activities/ForEach.cs

@@ -1,8 +1,8 @@
 using System.Text.Json.Serialization;
 using Elsa.Attributes;
+using Elsa.Behaviors;
 using Elsa.Contracts;
 using Elsa.Models;
-using Elsa.Signals;
 
 namespace Elsa.Activities;
 
@@ -13,7 +13,7 @@ public class ForEach : Activity
 
     public ForEach()
     {
-        OnSignalReceived<BreakSignal>(OnBreakAsync);
+        Behaviors.Add<BreakBehavior>();
     }
 
     /// <summary>
@@ -67,18 +67,6 @@ public class ForEach : Activity
     {
         await HandleIteration(context);
     }
-    
-    private async ValueTask OnBreakAsync(BreakSignal signal, SignalContext context)
-    {
-        // Prevent bubbling.
-        context.StopPropagation();
-
-        // Remove child activity execution contexts.
-        context.ActivityExecutionContext.RemoveChildren();
-
-        // Mark this activity as completed.
-        await context.ActivityExecutionContext.CompleteActivityAsync();
-    }
 }
 
 public class ForEach<T> : ForEach

src/core/Elsa.Core/Activities/While.cs

@@ -1,8 +1,8 @@
 using System.Text.Json.Serialization;
 using Elsa.Attributes;
+using Elsa.Behaviors;
 using Elsa.Contracts;
 using Elsa.Models;
-using Elsa.Signals;
 
 namespace Elsa.Activities;
 
@@ -18,8 +18,7 @@ public class While : Activity
     public While(IActivity? body = default)
     {
         Body = body!;
-        
-        OnSignalReceived<BreakSignal>(OnBreakAsync);
+        Behaviors.Add<BreakBehavior>();
     }
 
     public While(Input<bool> condition, IActivity? body = default) : this(body)
@@ -67,16 +66,4 @@ public class While : Activity
         else
             await context.CompleteActivityAsync();
     }
-    
-    private async ValueTask OnBreakAsync(BreakSignal signal, SignalContext context)
-    {
-        // Prevent bubbling.
-        context.StopPropagation();
-
-        // Remove child activity execution contexts.
-        context.ActivityExecutionContext.RemoveChildren();
-
-        // Mark this activity as completed.
-        await context.ActivityExecutionContext.CompleteActivityAsync();
-    }
 }

src/core/Elsa.Core/Behaviors/BreakBehavior.cs

@@ -0,0 +1,33 @@
+using Elsa.Contracts;
+using Elsa.Models;
+using Elsa.Signals;
+
+namespace Elsa.Behaviors;
+
+/// <summary>
+/// Implements a "break" behavior that handles the <see cref="BreakSignal"/> signal.
+/// </summary>
+public class BreakBehavior : IBehavior
+{
+    public async ValueTask HandleSignalAsync(object signal, SignalContext context)
+    {
+        if (signal is not BreakSignal breakSignal)
+            return;
+
+        await OnBreakAsync(breakSignal, context);
+    }
+
+    public ValueTask ExecuteAsync(ActivityExecutionContext context) => ValueTask.CompletedTask;
+
+    private async ValueTask OnBreakAsync(BreakSignal signal, SignalContext context)
+    {
+        // Prevent bubbling.
+        context.StopPropagation();
+
+        // Remove child activity execution contexts.
+        context.ActivityExecutionContext.RemoveChildren();
+
+        // Mark this activity as completed.
+        await context.ActivityExecutionContext.CompleteActivityAsync();
+    }
+}

src/core/Elsa.Core/Contracts/IBehavior.cs

@@ -0,0 +1,11 @@
+using Elsa.Models;
+
+namespace Elsa.Contracts;
+
+public interface IBehavior : ISignalHandler
+{
+    /// <summary>
+    /// Invoked when the activity executes.
+    /// </summary>
+    ValueTask ExecuteAsync(ActivityExecutionContext context);
+}

src/core/Elsa.Core/Contracts/ISignalHandler.cs

@@ -2,7 +2,7 @@ using Elsa.Models;
 
 namespace Elsa.Contracts;
 
-public interface ISignalHandler : IActivity
+public interface ISignalHandler
 {
     ValueTask HandleSignalAsync(object signal, SignalContext context);
 }

src/core/Elsa.Core/Extensions/BehaviorCollectionExtensions.cs

@@ -0,0 +1,8 @@
+using Elsa.Contracts;
+
+namespace Elsa;
+
+public static class BehaviorCollectionExtensions
+{
+    public static void Add<T>(this ICollection<IBehavior> behaviors) where T : IBehavior => behaviors.Add((T)Activator.CreateInstance(typeof(T))!);
+}

src/core/Elsa.Core/Models/Activity.cs

@@ -5,9 +5,10 @@ using Elsa.Signals;
 
 namespace Elsa.Models;
 
-public abstract class Activity : ISignalHandler
+public abstract class Activity : IActivity, ISignalHandler
 {
     private readonly ICollection<SignalHandlerRegistration> _signalHandlers = new List<SignalHandlerRegistration>();
+    
     protected Activity()
     {
         TypeName = TypeNameHelper.GenerateTypeName(GetType());
@@ -25,6 +26,8 @@ public abstract class Activity : ISignalHandler
     public IDictionary<string, object> ApplicationProperties { get; set; } = new Dictionary<string, object>();
     public IDictionary<string, object> Metadata { get; set; } = new Dictionary<string, object>();
     
+    public ICollection<IBehavior> Behaviors { get; } = new List<IBehavior>();
+    
     /// <summary>
     /// A value indicating whether this activity should complete automatically.
     /// Default is true.
@@ -89,6 +92,9 @@ public abstract class Activity : ISignalHandler
     async ValueTask IActivity.ExecuteAsync(ActivityExecutionContext context)
     {
         await ExecuteAsync(context);
+        
+        // Invoke behaviors.
+        foreach (var behavior in Behaviors) await behavior.ExecuteAsync(context);
     }
 
     async ValueTask ISignalHandler.HandleSignalAsync(object signal, SignalContext context)
@@ -102,6 +108,9 @@ public abstract class Activity : ISignalHandler
 
         foreach (var registration in handlers)
             await registration.Handler(signal, context);
+        
+        // Invoke behaviors.
+        foreach (var behavior in Behaviors) await behavior.HandleSignalAsync(signal, context);
     }
 }