Nullable in C# and Its Use

Introduction:

• Dot Net have two types of data types- Value type and Reference type. Reference type variables can contain null values but Value type variable cannot be null.
  
  
• Nullable allows value type variables to be assigned null like a reference type.
  
  
• Nullable will add Null value to existing datatype.

Syntax:

 

System.Nullable<T> variable       -or- T? variable

T can be any value type.

 

e.g. By default Bool can have values True, False.

Bool ?isTrue will have values True, False and Null.

Dot Net provides two properties:

• HasValue
• Value

HasValue:

• It is of type bool. It is set to true when the variable contains a non-null value.
• You Can use this property to check if variable contains value or not.

Value:

When variable's HasValue property is True, then you should use Value property to access the value of the variable.

Source Code: 

//Nullable Declaration
int? num1 = null;

//Below line will throw System.InvalidOperationException
//Error Message: Nullable object must have a value.
 Console.WriteLine(num1.Value);

//HasValue
if (!num1.HasValue)
{
           Console.WriteLine("num1 contains the Null value");
}
else
{
             //Access Value
             Console.WriteLine(num1.Value);
}

Practical use of Nullable:

e.g. the value in database is null.

e.g. When deserializing the data from xml or json,

It becomes difficult to deal with the situation if the value type property expects a value and it is not present in the source.

Nested nullable types are not allowed.

Nullable<Nullable<string>> str1;