Non-static method requires a target in PropertyInfo.SetValue

Question

Ok, so I'm learning about generics and I'm trying to make this thing run, but its keep saying me the same error. Here's the code:

    public static T Test<T>(MyClass myClass) where T : MyClass2
    {
        var result = default(T);
        var resultType = typeof(T);
        var fromClass = myClass.GetType();
        var toProperties = resultType.GetProperties();

        foreach (var propertyInfo in toProperties)
        {
            var fromProperty = fromClass.GetProperty(propertyInfo.Name);
            if (fromProperty != null)
                propertyInfo.SetValue(result, fromProperty, null );
        }

        return result;
    }

Answer 1

The problem here is that T derives from MyClass and is hence a reference type. So the expression default(T) will return the value null. The following call to SetValue is operating an a null value but the property is an instance property hence you get the specified message.

You'll need to do one of the following

1. Pass a real instance of T to the Test function to set the property values on
2. Only set the static properties on the type

Answer 2

This happens because default(T) returns null because T represents a reference type. Default values for reference types are null.

You could change your method to:

public static T Test<T>(MyClass myClass) where T : MyClass2, new()
{
    var result = new T();
    ...
}

and then it will work as you want it to. Of course, MyClass2 and its descendants must have a parameterless constructor now.