Today, I ran into something I didn't quite expect. I'm sure there is
a logical explanation for it so I want to post it and see if anyone
can explain the difference to me.
I came across a situation when I wanted to see if a public variable
inside a struct was null or not. Sample code below:
namespace SampleConsole
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Init
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main(string[] args)
{
MyStruct theStruct = new MyStruct();
theStruct.Variable1 = null;
try
{
if (theStruct.Variable1.Equals(null))
Console.WriteLine(".Equals evaluated");
}
catch
{
}
try
{
if (Convert.ReferenceEquals(theStruct.Variable1, null))
Console.WriteLine("ReferenceEquals evaluated");
}
catch
{
}
}
}
public struct MyStruct
{
public string Variable1;
public string Variable2;
}
}
What I found out was that theStruct.Variable1.Equals(null) throws an
System.NullReferenceException while
Convert.ReferenceEquals(theStruct.Variable1, null) returns true.
Well, there is clearly a difference between the two methods.
Looking in the MSDN library, I found the following definitions for the
two methods:
Object.Equals method: Determines whether two Object instances are
equal.
Convert.ReferenceEquals method: Determines whether the specified
Object instances are the same instance.
Well, I fail to see the difference in the two definitions. Being the
engineer that I am, I thought well let me look up the definition of a
System.NullReferenceException and the MSDN library offers:
The exception that is thrown when there is an attempt to dereference a
null object reference.
This doesn't help any either. Any thoughts?
