C# Antipatterns

Question

To cut a long story short: I find the Java antipatterns an indispensable resource. For beginners as much as for professionals. I have yet to find something like this for C#. So I'll open up this question as community wiki and invite everyone to share their knowledge on this. As I am new to C#, I am strongly interested in this, but cannot start with some antipatterns :/

Here are the answers which I find specifically true for C# and not other languages.

I just copy/pasted these! Consider throwing a look on the comments on these as well.

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Throwing NullReferenceException

Throwing the wrong exception:

if (FooLicenceKeyHolder == null)
    throw new NullReferenceException();

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Properties vs. public Variables

Public variables in classes (use a property instead).

Unless the class is a simple Data Transfer Object.

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Not understanding that bool is a real type, not just a convention

if (myBooleanVariable == true)
{
    ...
}

or, even better

if (myBooleanVariable != false)
{
    ...
}

Constructs like these are often used by C and C++ developers where the idea of a boolean value was just a convention (0 == false, anything else is true); this is not necessary (or desirable) in C# or other languages that have real booleans.

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Using using()

Not making use of using where appropriate:

object variable;
variable.close(); //Old code, use IDisposable if available.
variable.Dispose(); //Same as close.  Avoid if possible use the using() { } pattern.
variable = null; //1. in release optimised away.  2. C# is GC so this doesn't do what was intended anyway.

Answer 1

Rethrowing the exception incorrectly. To rethrow an exception :

try
{
    // do some stuff here
}
catch (Exception ex)
{
    throw ex;  // INCORRECT
    throw;     // CORRECT
    throw new Exception("There was an error"); // INCORRECT
    throw new Exception("There was an error", ex); // CORRECT
}