Is it possible to set private property via reflection?

Can I set a private property via reflection?

public abstract class Entity
{
    private int _id;
    private DateTime? _createdOn;
    public virtual T Id
    {
        get { return _id; }
        private set { ChangePropertyAndNotify(ref _id, value, x => Id); }
    }
    public virtual DateTime? CreatedOn
    {
        get { return _createdOn; }
        private set { ChangePropertyAndNotify(ref _createdOn, value, x => CreatedOn); }
    }
}

I've tried the following and it does not work, where t represents a type of Entity:

var t = typeof(Entity);
var mi = t.GetMethod("set_CreatedOn", BindingFlags.Instance | BindingFlags.NonPublic);

I guess I can do this but I can't work it out.

Yes, it is:

/// <summary>
/// Returns a _private_ Property Value from a given Object. Uses Reflection.
/// Throws a ArgumentOutOfRangeException if the Property is not found.
/// </summary>
/// <typeparam name="T">Type of the Property</typeparam>
/// <param name="obj">Object from where the Property Value is returned</param>
/// <param name="propName">Propertyname as string.</param>
/// <returns>PropertyValue</returns>
public static T GetPrivatePropertyValue<T>(this object obj, string propName)
{
	if (obj == null) throw new ArgumentNullException("obj");
	PropertyInfo pi = obj.GetType().GetProperty(propName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
	if (pi == null) throw new ArgumentOutOfRangeException("propName", string.Format("Property {0} was not found in Type {1}", propName, obj.GetType().FullName));
	return (T)pi.GetValue(obj, null);
}

/// <summary>
/// Returns a private Property Value from a given Object. Uses Reflection.
/// Throws a ArgumentOutOfRangeException if the Property is not found.
/// </summary>
/// <typeparam name="T">Type of the Property</typeparam>
/// <param name="obj">Object from where the Property Value is returned</param>
/// <param name="propName">Propertyname as string.</param>
/// <returns>PropertyValue</returns>
public static T GetPrivateFieldValue<T>(this object obj, string propName)
{
	if (obj == null) throw new ArgumentNullException("obj");
	Type t = obj.GetType();
	FieldInfo fi = null;
	while (fi == null && t != null)
	{
		fi = t.GetField(propName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
		t = t.BaseType;
	}
	if (fi == null) throw new ArgumentOutOfRangeException("propName", string.Format("Field {0} was not found in Type {1}", propName, obj.GetType().FullName));
	return (T)fi.GetValue(obj);
}

/// <summary>
/// Sets a _private_ Property Value from a given Object. Uses Reflection.
/// Throws a ArgumentOutOfRangeException if the Property is not found.
/// </summary>
/// <typeparam name="T">Type of the Property</typeparam>
/// <param name="obj">Object from where the Property Value is set</param>
/// <param name="propName">Propertyname as string.</param>
/// <param name="val">Value to set.</param>
/// <returns>PropertyValue</returns>
public static void SetPrivatePropertyValue<T>(this object obj, string propName, T val)
{
	Type t = obj.GetType();
	if (t.GetProperty(propName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance) == null)
		throw new ArgumentOutOfRangeException("propName", string.Format("Property {0} was not found in Type {1}", propName, obj.GetType().FullName));
	t.InvokeMember(propName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.SetProperty | BindingFlags.Instance, null, obj, new object[] { val });
}

/// <summary>
/// Set a private Property Value on a given Object. Uses Reflection.
/// </summary>
/// <typeparam name="T">Type of the Property</typeparam>
/// <param name="obj">Object from where the Property Value is returned</param>
/// <param name="propName">Propertyname as string.</param>
/// <param name="val">the value to set</param>
/// <exception cref="ArgumentOutOfRangeException">if the Property is not found</exception>
public static void SetPrivateFieldValue<T>(this object obj, string propName, T val)
{
	if (obj == null) throw new ArgumentNullException("obj");
	Type t = obj.GetType();
	FieldInfo fi = null;
	while (fi == null && t != null)
	{
		fi = t.GetField(propName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
		t = t.BaseType;
	}
	if (fi == null) throw new ArgumentOutOfRangeException("propName", string.Format("Field {0} was not found in Type {1}", propName, obj.GetType().FullName));
	fi.SetValue(obj, val);
}

t.GetProperty("CreatedOn")
    .SetValue(obj, new DateTime(2009, 10, 14), null);

EDIT: Since the property itself is public, you apparently don't need to use BindingFlags.NonPublic to find it. Calling SetValue despite the the setter having less accessibility still does what you expect.

You can access private setter from derived type via code

public static void SetProperty(object instance, string propertyName, object newValue)
{
    Type type = instance.GetType();

    PropertyInfo prop = type.BaseType.GetProperty(propertyName);

    prop.SetValue(instance, newValue, null);
}

None of these worked for me, and my property name was unique, so I just used this:

public static void SetPrivatePropertyValue<T>(T obj, string propertyName, object newValue)
{
	// add a check here that the object obj and propertyName string are not null
	foreach (FieldInfo fi in obj.GetType().GetFields(BindingFlags.Instance | BindingFlags.NonPublic))
	{
		if (fi.Name.ToLower().Contains(propertyName.ToLower()))
		{
			fi.SetValue(obj, newValue);
			break;
		}
	}
}

    //mock class
    public class Person{
    	public string Name{get; internal set;}
    }
    
    // works for all types, update private field through reflection
    public static T ReviveType<T>(T t, string propertyName, object newValue){
    	// add a check here that the object t and propertyName string are not null
    	PropertyInfo pi = t.GetType().GetProperty(propertyName, BindingFlags.Public | BindingFlags.Instance);
    	 pi.SetValue(t, newValue, null); 
    	return t;
    }
    
    // check the required function
    void Main()
    {
    	var p = new Person(){Name="John"};
    	Console.WriteLine("Name: {0}",p.Name);
    	
    	//box the person to object, just to see that the method never care about what type you pass it
    	object o = p;
    	var updatedPerson = ReviveType<Object>(o, "Name", "Webber") as Person;
    	 
    	 //check if it updated person instance
    	Console.WriteLine("Name: {0}",updatedPerson.Name);
    }



// Console Result: -------------------
Name: John
Name: Webber