Get property of generic class

Question

I have a generic class, and an object value where obj.GetType().GetGenericTypeDefinition() == typeof(Foo<>).

class Foo<T>
{
    public List<T> Items { get; set; }
}

How do I get the value of Items from obj? Remember, obj is an Object, I can't cast obj as Foo because I don't know what T is.

I was hoping to use reflection for this, but each time I do GetProperty("Items") it returns null. However, if someone knows a good way to do this without reflection, by all means.

Let's say my code looks like this:

//just to demonstrate where this comes from
Foo<int> fooObject = new Foo<int>();
fooObject.Items = someList;
object obj = (object)fooObject;

//now trying to get the Item value back from obj
//assume I have no idea what <T> is
PropertyInfo propInfo = obj.GetType().GetProperty("Items"); //this returns null
object itemValue = propInfo.GetValue(obj, null); //and this breaks because it's null

Answer 1

You should be able to use:

Type t = obj.GetType();

PropertyInfo prop = t.GetProperty("Items");

object list = prop.GetValue(obj);

You will not be able to cast as a List<T> directly, of course, as you don't know the type T, but you should still be able to get the value of Items.

---

Edit:

The following is a complete example, to demonstrate this working:

// Define other methods and classes here
class Foo<T>
{
    public List<T> Items { get; set; }
}

class Program
{
    void Main()
    {   
        //just to demonstrate where this comes from
        Foo<int> fooObject = new Foo<int>();
        fooObject.Items = new List<int> { 1, 2, 3};
        object obj = (object)fooObject;

        //now trying to get the Item value back from obj
        //assume I have no idea what <T> is
        PropertyInfo propInfo = obj.GetType().GetProperty("Items"); //this returns null
        object itemValue = propInfo.GetValue(obj, null);

        Console.WriteLine(itemValue);
                    // Does not print out NULL - prints out System.Collections.Generic.List`1[System.Int32]


        IList values = (IList)itemValue;
        foreach(var val in values)
            Console.WriteLine(val); // Writes out values appropriately
    }
}

Answer 2

@ReedCopsey is absolutely correct, but in case you're really asking the question "How do I fish out the generic details of a type?", here's some "Fun with Reflection":

public void WhatsaFoo(object obj)
{
    var genericType = obj.GetType().GetGenericTypeDefinition();
    if(genericType == typeof(Foo<>))
    {
        // Figure out what generic args were used to make this thing
        var genArgs = obj.GetType().GetGenericArguments();

        // fetch the actual typed variant of Foo
        var typedVariant = genericType.MakeGenericType(genArgs);

        // alternatively, we can say what the type of T is...
        var typeofT = obj.GetType().GetGenericArguments().First();

        // or fetch the list...
        var itemsOf = typedVariant.GetProperty("Items").GetValue(obj, null);
    }
}

Answer 3

Something like this should do the trick:

var foo = new Foo<int>();
foo.Items = new List<int>(new int[]{1,2,3});

// this check is probably not needed, but safety first :)
if (foo.GetType().GetProperties().Any(p => p.Name == "Items"))
{
    var items = foo.GetType().GetProperty("Items").GetValue(foo, null);
}

Answer 4

You have to use System.Reflection namespace to execute the program successfully.

This program gives you Property Name and Value of any Generic Class

You can check this code fiddle on C# Online Rexter Tool Compiler at

using System;
using System.Reflection;

namespace GenericPropertyExample
{
    //Declaring a Sample Class 
    public class class1
    {
        public string prop1 { get; set; }
        public string prop2 { get; set; }

    }
    public class Program
    {
        public static void Main(string[] args)
        {
            //Creating Class Object
            class1 objClass1 = new class1 { prop1 = "value1", prop2 = "value2" };

            //Passing Class Object to GenericPropertyFinder Class
            GenericPropertyFinder<class1> objGenericPropertyFinder = new GenericPropertyFinder<class1>();
            objGenericPropertyFinder.PrintTModelPropertyAndValue(objClass1);
            Console.ReadLine();
        }

        //Declaring a Generic Handler Class which will actually give Property Name,Value for any given class.
        public class GenericPropertyFinder<TModel> where TModel : class
        {
            public void PrintTModelPropertyAndValue(TModel tmodelObj)
            {
                //Getting Type of Generic Class Model
                Type tModelType = tmodelObj.GetType();

                //We will be defining a PropertyInfo Object which contains details about the class property 
                PropertyInfo[] arrayPropertyInfos = tModelType.GetProperties();

                //Now we will loop in all properties one by one to get value
                foreach (PropertyInfo property in arrayPropertyInfos)
                {
                    Console.WriteLine("Name of Property is\t:\t" + property.Name);
                    Console.WriteLine("Value of Property is\t:\t" + property.GetValue(tmodelObj).ToString());
                    Console.WriteLine(Environment.NewLine);
                }
            }
        }
    }
}

Answer 5

Hey guys ive been struggeling with the same issue with generic typs and finally found the solution that gets the value --------Small code snippet of the method that does the trick ------------------

    public void printFields()
    {
        // Is the list empty
        if (this.list_.Count == 0)
        {
            //Y => Forced exit no object info
            return;
        }

        try
        {
            // Get first item from list
            T item = this.list_[0];

            // Get the type of object
            //**Type thisType = item.GetType();

            // Get array of all fields
            FieldInfo[] thisFieldInfo = item.GetType().GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

            // Loop through all fields and show its info
            for (int ix = 0; ix < thisFieldInfo.Length; ix++)
            {
                // Get Field value
                String strVal = thisFieldInfo[ix].GetValue(item).ToString();

                // Display item
                Console.WriteLine("'{0}' is a {1} and has value {2}", thisFieldInfo[ix].Name, thisFieldInfo[ix].FieldType, strVal);
            }


        }
        catch (SecurityException e)
        {
            Console.WriteLine("Exception: " + e.Message);
        }
    }