LA0107: Instance Advice Applied to a Static Member


Severity	Error
Reported by	PostSharp
Message	`Cannot apply an instance advice of the instance-scoped aspect "<Aspect>" to the static member "<Member>" (make the advice static).`

Cause

An instance-scoped aspect, such as an InstanceLevelAspect applied to a class, has one instance for each instance of its target class. An advice method that is not static runs on this aspect instance. A static member, such as a static property, is not related to any instance of the class, so no aspect instance exists to run the advice.

When the pointcut of an instance advice method selects a static member, PostSharp reports LA0107 on that member. This often happens with a MulticastPointcut that sets only Targets, which selects the static members as well as the instance ones.

In the following example, the pointcut of the [TrackChanges] aspect selects all the properties of Customer, including the static Count property.

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

namespace Errors.LA0107_Error;

[PSerializable]
public class TrackChangesAttribute : InstanceLevelAspect
{
    [OnLocationSetValueAdvice, MulticastPointcut( Targets = MulticastTargets.Property )]
    public void OnPropertySet( LocationInterceptionArgs args )
    {
        Console.WriteLine( $"Setting {args.LocationName} to {args.Value}." );
        args.ProceedSetValue();
    }
}

[TrackChanges]
public class Customer
{
    // The pointcut selects this static property, but the advice is an instance method of an instance-level aspect.
    public static int Count { get; set; }

    public string? Name { get; set; }
}

public static class Program
{
    public static void Main()
    {
        Customer.Count = 1;
        new Customer().Name = "Alice";
    }
}

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error LA0107: LA0107_Error.cs(24,23): Cannot apply an instance advice of the instance-scoped aspect "Errors.LA0107_Error.TrackChangesAttribute" to the static member "Errors.LA0107_Error.Customer.Count" (make the advice static).

Resolution

Exclude the static members from the pointcut, for instance with Attributes = MulticastAttributes.Instance in the MulticastPointcut, or by filtering them out in the method of a MethodPointcut.
Or make the advice method static, as the message suggests, when it does not use the state of the aspect instance. PostSharp does not report LA0107 for a static advice method.

In the following example, the pointcut selects only the instance properties, so the advice does not apply to Count.

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

namespace Errors.LA0107_Fixed;

[PSerializable]
public class TrackChangesAttribute : InstanceLevelAspect
{
    // The pointcut selects only the instance properties.
    [OnLocationSetValueAdvice, MulticastPointcut( Targets = MulticastTargets.Property, Attributes = MulticastAttributes.Instance )]
    public void OnPropertySet( LocationInterceptionArgs args )
    {
        Console.WriteLine( $"Setting {args.LocationName} to {args.Value}." );
        args.ProceedSetValue();
    }
}

[TrackChanges]
public class Customer
{
    public static int Count { get; set; }

    public string? Name { get; set; }
}

public static class Program
{
    public static void Main()
    {
        Customer.Count = 1;
        new Customer().Name = "Alice";
    }
}

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Setting Name to Alice.

Cause

Resolution

See Also