Import postsharp aspect field from class by name dynamically

Question

If I have a class:

class MyClass
{
  IMyInterface _mi;

  [MyAspectAttribute("_mi")]
  bool _myValue;

  // ...
}

Is there a way to create an aspect attribute MyAspectAttribute that intercepts getting and setting the value for (bool myValue) AND also imports the field that is specified in the attribute [MyAspectAttribute("_mi")] in this case _mi dynamically so I can use it in the aspect? (I want to call the interface before getting or setting the field in the aspect).

I know how to write the aspect I just don't know how to dynamically import the specified field (in this example _mi). All of the examples require that you know the exact field name to import (but I want the name passed to my aspect).

Thanks.

Answer 1

You can import the field dynamically by implementing IAdviceProvider.ProvideAdvices method and returning ImportLocationAdviceInstance for the field you want to import. The sample aspect below demonstrates this technique.

[PSerializable]
public class MyAspectAttribute : LocationLevelAspect, IAdviceProvider, IInstanceScopedAspect
{
    private string _importedFieldName;

    public MyAspectAttribute(string importedFieldName)
    {
        _importedFieldName = importedFieldName;
    }

    public ILocationBinding ImportedField;

    public IEnumerable<AdviceInstance> ProvideAdvices(object targetElement)
    {
        var target = (LocationInfo) targetElement;
        var importedField = target.DeclaringType
            .GetFields(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)
            .First(f => f.Name == this._importedFieldName);

        yield return new ImportLocationAdviceInstance(
            typeof(MyAspectAttribute).GetField("ImportedField"),
            new LocationInfo(importedField));
    }

    [OnLocationGetValueAdvice, SelfPointcut]
    public void OnGetValue(LocationInterceptionArgs args)
    {
        IMyInterface mi = (IMyInterface)this.ImportedField.GetValue(args.Instance);
        mi.SomeMethod();

        args.ProceedGetValue();
    }

    [OnLocationSetValueAdvice(Master = "OnGetValue"), SelfPointcut]
    public void OnSetValue(LocationInterceptionArgs args)
    {
        IMyInterface mi = (IMyInterface) this.ImportedField.GetValue(args.Instance);
        mi.SomeMethod();

        args.ProceedSetValue();
    }

    public object CreateInstance(AdviceArgs adviceArgs)
    {
        return this.MemberwiseClone();
    }

    public void RuntimeInitializeInstance()
    {
    }
}