Working with null values in the .NET Framework

One of the interesting aspect of application development is handling null/zero/non existing/non allocated values. We can say like "our code is expecting some value for a variable but it got nothing or some unexpected value" and this is the places where we have use proper null checking to make the system stable.

Null - The Most Common

A null value is a value that doesn't refer toany object. It's the default value of reference-type variables.

    1:  struct sTest

   2:  {
   3:      public string teststring;
   4:  }    
   5:   
   6:  sTest obj = new sTest();
   7:  if (obj.teststring == null) {
   8:  Console.WriteLine("sTest is Null")   9:  } }

This code works without any problems with C#,but,VB.NET uses the Nothing keyword. The following code demonstrate its use:

   1:  Dim sTest As String

   2:  If (sTest Is Nothing) Then

   3:  Console.WriteLine("sTest is Null")

   4:  End If

Another area of confusion stems from the factthat VB.NET doesn't treat null and Nothing as equals; consequently,a VB.NET programmer may have to check for both values.

Microsoft provides a uniform method for working with null values: The base System.Convert namespace includes the DBNull object.

DBNull

The use of the DBNull class indicates the absence of a known value. While the Microsoft documentation says it's typically in a database application, you may also use it withany type of data.

In database applications, a null object is avalid value for a field. This class differentiates between a null value (a null object) and an uninitialized value (the DBNull.Value instance). For example, a table can have records with uninitialized fields. By default, these uninitialized fields have the DBNullvalue.

You can utilize the DBNull object by way of its Value property. This represents a null value, which is never equal to anything. The following C# snippet revises the previous example to utilize the DBNull class:

   1:  if (sTest.Equals(System.DBNull.Value)) {

   2:  Console.WriteLine("sTest is null.");

same code, like this:

If (sTest.Equals(System.DBNull.Value) Then
Console.WriteLine("sTest is Null")
End If

You may also use the DBNull.Value constant on the right-hand of an assignment operation, thus storing a null value within a reference type. In addition, the .NET Frameworkprovides the IsDBNull function (in the System.Convert namespace),which is a shorthand approach for determining if a reference type contains a null value. The following VB.NET uses IsDBNull to checkan object's value:

   1:  Dim oTest As Object = DBNull.Value

   2:  If ((IsDBNull(oTest))) Then

   3:  Console.WriteLine("oTest is Null")

   4:  End If

Even if you check for null values at every conceivable location within your code, they still may creep into the application. So you have to provide the try/catch exception block; it allows you to catch any unhandled exceptions that null values cause. The System namespace provides the NullReferenceException for these situations.

   1:  try {

   2:   

   3:  if (sTest.Equals(System.DBNull.Value)) {

   4:  Console.WriteLine("sTest is null.");

   5:  }

   6:   

   7:  } catch (System.NullReferenceException e) {

   8:  Console.WriteLine("Error: " + e.ToString());

9: }Handle your data with care

So now you have a uniform mechanism for checking any uninitialized references in your application.......