Question

I have a class derived from base class which has a private field.
How can I get the BaseType field value?

public class SuperClass : BaseClass
{
}

public class BaseClass
{
    private object theField;
}

I have the SuperClass instance and the code should be something like:

var baseType = super.GetType().BaseType;
var fieldInfo = baseType.GetField("theField", BindingFlags.NonPublic | BindingFlags.Instance);

Now how can I get the value from fieldInfo? Or my approach is wrong?

Answer 1

Use FieldInfo.GetValue

fieldInfo.GetValue(this)

Incidentally you don’t need super.GetType – you can just do:

this.GetType().BaseType

Equally, since you know the base type – it’s possibly marginally quicker to do

typeof(BaseClass).GetField("theField" ....)

Update

I used this because your question implies that the code you’ve written is part of SuperClass because you have written (despite it not being valid C#):

var baseType = super.GetType().BaseType; 

If that’s not the case, and you have an instance of SuperClass then this will do:

var obj = new SuperClass();
var privateValue = typeof(BaseClass).GetField("theField", 
  BindingFlags.NonPublic | BindingFlags.Instance).GetValue(obj);

I would actually strongly recommend against using obj.GetType().BaseType – because your reflection will immediately break if you choose to inject a base between SuperClass and BaseClass; whereas using typeof(BaseClass) won’t – unless you actually remove BaseClass from SuperClass‘s inheritance tree.