How call a specific method from property aspect with property name and prefix?

Question

I want to develop a NotifyDataErrorInfoAspect with possharp.

The validation of the values depends on several changeable properties (MinValue, MaxValue ...). The contract can't work with variable parameters.

I want to build something similar to the DependencyPropertyAspect. Each property with [DependencyProperty] has a number of optional methods. For example ValidatePropertyName.

[DependencyProperty]
public string Email { get; set; }

private bool ValidateEmail(string value)
{
    return EmailRegex.IsMatch(value);
}

How can I do this?

[NotifyDataErrorInfo]
public string Name{ get; set; }
private IList<DataErrorInfo> ValidateName(string value)
{
    return this.IsValidName(value);
}

[NotifyDataErrorInfo]
public int Age{ get; set; }
private IList<DataErrorInfo> ValidateAge(int value)
{
    return this.IsValidAge(value);
}

[NotifyDataErrorInfo]
public string Email { get; set; }
private IList<DataErrorInfo> ValidateEmail(string value)
{
    return this.IsValidEmail(value);
}

The attribute ImportMethod () only allows a fixed method name. What is the best way?

Answer 1

When you need to import a method that doesn't have a fixed predefined name, you can implement IAdviceProvider interface in your aspect and provide ImportMethodAdviceInstance that takes a method name as a string argument.

Another important point is that your Validate methods take arguments of a specific type instead of object. Currently, it's not possible to create a generic attribute in C#, so you need to create two aspect classes to handle this case: an attribute that is an aspect provider and a generic aspect implementation.

Below is a sample implementation of NotifyDataErrorInfo aspect:

[PSerializable]
public class NotifyDataErrorInfoAttribute : LocationLevelAspect, IAspectProvider
{
    public IEnumerable<AspectInstance> ProvideAspects(object targetElement)
    {
        Type propertyType = ((LocationInfo)targetElement).LocationType;
        Type aspectType = typeof(NotifyDataErrorInfoAspectImpl<>).MakeGenericType(propertyType);

        yield return new AspectInstance(
            targetElement, (IAspect) Activator.CreateInstance(aspectType));
    }
}

[PSerializable]
public class NotifyDataErrorInfoAspectImpl<T> : ILocationInterceptionAspect,
                                                IInstanceScopedAspect,
                                                IAdviceProvider
{
    public Func<T, IList<DataErrorInfo>> ValidateDelegate;

    public IEnumerable<AdviceInstance> ProvideAdvices(object targetElement)
    {
        LocationInfo property = (LocationInfo)targetElement;
        string validateMethodName = "Validate" + property.Name;

        yield return new ImportMethodAdviceInstance(
            typeof(NotifyDataErrorInfoAspectImpl<>).GetField("ValidateDelegate"),
            validateMethodName,
            true);
    }

    public void OnSetValue(LocationInterceptionArgs args)
    {
        if (ValidateDelegate((T) args.Value)?.Any() == true)
            throw new ArgumentException("...");

        args.ProceedSetValue();
    }

    public void OnGetValue(LocationInterceptionArgs args)
    {
        args.ProceedGetValue();
    }

    public void RuntimeInitialize(LocationInfo locationInfo)
    {
    }

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

    public void RuntimeInitializeInstance()
    {
    }
}