LA0224: Binding Not Supported in an Instance Constructed Advice


Severity	Error
Reported by	PostSharp
Message	`The parameter "<Parameter>" of the advice "<Advice>" is bound by <Binding>, which a method annotated with [OnInstanceConstructedAdvice] does not support.`

Cause

An advice method annotated with OnInstanceConstructedAdvice runs once an object of the target type is constructed, whichever constructor ran. It runs in a method without parameters, and its target is the type, not a method. It therefore has no argument, no return value, no field or property value and no control flow to change. When a parameter of this advice is bound by ArgumentAttribute, ReturnValueAttribute, LocationValueAttribute or FlowBehaviorAttribute, PostSharp reports LA0224 on the parameter.

<Binding> is the binding attribute as you wrote it, such as [Argument("name")]. The other binding attributes that this advice does not accept report LA0151.

In the following example, the instance constructed advice of the [TraceCreation] aspect tries to receive the name argument of the constructor of Customer.

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using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Advices;
using PostSharp.Serialization;

namespace Errors.LA0224_Error;

[PSerializable]
public sealed class TraceCreationAttribute : InstanceLevelAspect
{
    // The advice runs after any constructor, so it has no argument to receive.
    [OnInstanceConstructedAdvice]
    public void OnInstanceConstructed( [Argument( "name" )] string name )
    {
        Console.WriteLine( $"Created {name}" );
    }
}

[TraceCreation]
public class Customer
{
    public Customer( string name )
    {
        this.Name = name;
    }

    public string Name { get; }

    public override string ToString() => $"Customer {this.Name}";
}

public static class Program
{
    public static void Main()
    {
        _ = new Customer( "Alice" );
    }
}

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error LA0224: LA0224_Error.cs(13,68): The parameter "name" of the advice "Errors.LA0224_Error.TraceCreationAttribute.OnInstanceConstructed(System.String)" is bound by [Argument("name")], which a method annotated with [OnInstanceConstructedAdvice] does not support.

Resolution

Receive the constructed object with a ThisAttribute parameter, and read the values that the constructor stored in it.
To receive the arguments of a constructor, apply a method-level aspect to the constructor instead, with an OnMethodEntryAdvice or OnMethodSuccessAdvice that binds them with ArgumentAttribute.

In the following example, the [TraceCreation] aspect receives the constructed Customer.

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using System;
using PostSharp.Aspects;
using PostSharp.Aspects.Advices;
using PostSharp.Serialization;

namespace Errors.LA0224_Fixed;

[PSerializable]
public sealed class TraceCreationAttribute : InstanceLevelAspect
{
    // The advice receives the constructed object, which holds the values passed to the constructor.
    [OnInstanceConstructedAdvice]
    public void OnInstanceConstructed( [This] object instance )
    {
        Console.WriteLine( $"Created {instance}" );
    }
}

[TraceCreation]
public class Customer
{
    public Customer( string name )
    {
        this.Name = name;
    }

    public string Name { get; }

    public override string ToString() => $"Customer {this.Name}";
}

public static class Program
{
    public static void Main()
    {
        _ = new Customer( "Alice" );
    }
}

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Created Customer Alice

Cause

Resolution

See Also