Reflecting Over Nested Instances without Creating New Instance

I have been struggling a bit with some reflection code that I though would be simple. Essentially, I have an interface that defines a method. Then, I have an abstract class that provides a base implementation of that method.

The concrete classes can contain nested instances of other classes that can also derive from the same base class. It can be illustrated by the following sample:

using System.Linq;

public interface ISampleObject
{
    bool IsValid();
}

public abstract class SampleObjectBase : ISampleObject
{
    public bool IsValid()
    {
        var returnValue = true;

        // Self-validation sets the return value.

        var childProperties = this.GetType().GetProperties().Where(pi => typeof(ISampleObject).IsAssignableFrom(pi.PropertyType));

        foreach (var childProperty in childProperties)
        {
            // var childInstance = ????;  // Need the actual *existing* instance property, cast to ISampleObject.
            // if (childInstance.IsValid() != true)
            // {
            //     returnValue = false;
            // }
        }

        return returnValue;
    }
}

public sealed class InnerSampleObject : SampleObjectBase
{
}

public sealed class OuterSampleObject : SampleObjectBase
{
    public InnerSampleObject DerivedSampleObject { get; set; }    
}

My problem is that in the commented code for SampleObjectBase, I cannot get the concrete instance of the matching PropertyInfo value. If I look at the PropertyInfo object in the loop, I see that the type is correct, but I cannot find a way to directly access the instance that already exists in the implementation. So, when executing, for example, OuterSampleObject.IsValid(), the code finds the PropertyInfo for InnerSampleObject, as expected. I want to execute InnerSampleObject.IsValid().

I have tried (multiple variations of):

var childIsValid = (bool)contractProperty.PropertyType.InvokeMember("IsValid", BindingFlags.InvokeMethod, null, null, null);

And:

var chi开发者_StackOverflowldInstance = (ISampleContract)contractProperty;

The problem with the first one is that I can't pass null in as the target for InvokeMember, as IsValid() is not static (nor can it be, since I am focused on the actual instance). The second on is just a lame cast, but is the gist of what I want to accomplish.

The sample code above is just a minimalist example of what I want to achieve. The full code is part of a self-validating DTO that recursively checks the entire hierarchy and returns what children have validation issues and what they are.

Any help would be greatly appreciated.

---

How about:

var instance = childProperty.GetValue(this, null) as ISampleObject;
if (instance != null)
{
  if (!instance.IsValid())
    return false;
}

---

Please see if the code below is what you are looking for. My changes are marked with a comment starting with //VH:

public interface ISampleObject
{
    bool IsValid();
}

public abstract class SampleObjectBase : ISampleObject
{
    public virtual bool IsValid()
    {
        var returnValue = true; //VH: Changed value from false to true

        // Self-validation sets the return value.

        var childProperties = this.GetType().GetProperties().Where(pi => typeof(ISampleObject).IsAssignableFrom(pi.PropertyType));

        foreach (var childProperty in childProperties)
        {
            //VH: Here is how you get the value of the property
            var childInstance = (ISampleObject)childProperty.GetValue(this, null);
            if (childInstance.IsValid() != true)                
            {
                 returnValue = false;
            }
        }

        return returnValue;
    }
}

public sealed class InnerSampleObject : SampleObjectBase
{
}

public sealed class OuterSampleObject : SampleObjectBase
{
    //VH: Added this constructor
    public OuterSampleObject()
    {
        DerivedSampleObject = new InnerSampleObject();
    }

    public InnerSampleObject DerivedSampleObject { get; set; }
}


class Program
{
    static void Main(string[] args)
    {
        OuterSampleObject c = new OuterSampleObject();
        c.IsValid();

    }
}

---

Just use

var childInstance = (ISampleObject)childProperty.GetValue(this, null);