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Checking if an object is null in C#

Asked 2011-06-20T21:40:36.130
324

I would like to prevent further processing on an object if it is null.

In the following code I check if the object is null by either:

if (!data.Equals(null))

and

if (data != null)

However, I receive a NullReferenceException at dataList.Add(data). If the object was null, it should never have even entered the if-statement!

Thus, I'm asking if this is proper way of checking if an object is null:

public List<Object> dataList;
public  bool AddData(ref Object data)
    bool success = false;
    try
    {
        // I've also used "if (data != null)" which hasn't worked either
        if (!data.Equals(null))
        {
           //NullReferenceException occurs here ...
           dataList.Add(data);
           success = doOtherStuff(data);
        }
    }
    catch (Exception e)
    {
        throw new Exception(e.ToString());
    }
    return success;
}

If this is the proper way of checking if the object is null, what am I doing wrong (how can I prevent further processing on the object to avoid the NullReferenceException)?

c# null nullreferenceexception
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1 Answer

22

[Edited to reflect hint by @kelton52]

Simplest way is to do object.ReferenceEquals(null, data)

Since (null==data) is NOT guaranteed to work:

class Nully
{
    public static bool operator ==(Nully n, object o)
    {
        Console.WriteLine("Comparing '" + n + "' with '" + o + "'");
        return true;
    }
    public static bool operator !=(Nully n, object o) { return !(n==o); }
}
void Main()
{
    var data = new Nully();
    Console.WriteLine(null == data);
    Console.WriteLine(object.ReferenceEquals(null, data));
}

Produces:

Comparing '' with 'Nully'

True

False

answered 2012-04-11T11:17:34.497

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