C# extension method to objects with specific attribute - serialization

Question

I created an extension method that will tell me the size of every object I create
like this:
public static int CalculateKilobytes(this object notSuspectingCandidate)
{
using (MemoryStream stream = new MemoryStream())
{
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(stream, notSuspectingCandidate);
return stream.ToArray().Count() / 1000;
}
}
Since I'm using serializaion, not all objects will be able to return answer, only the serializble ones. Is there a way to attach this method to an object that can be serialized?

Answer 1

you can use Type.IsSerializable Property.
public static int CalculateKilobytes(this object notSuspectingCandidate)
{
using (MemoryStream stream = new MemoryStream())
{
BinaryFormatter formatter = new BinaryFormatter();
if (notSuspectingCandidate.GetType().IsSerializable) {
formatter.Serialize(stream, notSuspectingCandidate);
return stream.ToArray().Count() / 1000;
}
return 0;
}
}

Answer 2

It's a really bad practice to serialize a object only to get its size, if you plan to serialize it again later.
Use with caution.
The extension method will be applied to all objects, you must check if it has the custom property in it.
This check can do the job.
if (notSuspectingCandidate.GetType().GetCustomAttributes(typeof(SerializableAttribute), true).Length == 0)
{
return -1; // An error
}
Another way is to put a extension method to ISerializable and use the interface in all your required types.
public static int CalculateKilobytes(this ISerializable notSuspectingCandidate)
{
using (MemoryStream stream = new MemoryStream())
{
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(stream, notSuspectingCandidate);
return stream.ToArray().Count() / 1000;
}
}