Null-conditional operator short-circuits the remainder of the expression. - CSharp Language Basics

CSharp examples for Language Basics:Null Operator

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Introduction

In the following example, s evaluates to null, even with a standard dot operator between ToString() and ToUpper():

Demo Code

using System;/*  ww  w . j av  a  2  s.  c o m*/
class Test
{
   static void Main(){
      System.Text.StringBuilder sb = null;
      string s = sb?.ToString().ToUpper();   // s evaluates to null without error
      Console.WriteLine(s);
   }
}

Repeated use of ?. is necessary only if the operand immediately to its left may be null.

The following expression is robust to both x being null and x.y being null: 

x?.y?.z

The final expression must be capable of accepting a null.

The following is illegal: 

System.Text.StringBuilder sb = null;
int length = sb?.ToString().Length;   // Illegal : int cannot be null

We can fix this with the use of nullable value types: 

int? length = sb?.ToString().Length;   // OK : int? can be null

You can also use the null-conditional operator to call a void method: 

someObject?.SomeVoidMethod();

If someObject is null, this becomes a "no-operation" rather than throwing a NullReferenceException.

Null-conditional operator combines well with the null-coalescing operator: 

System.Text.StringBuilder sb = null;
string s = sb?.ToString() ?? "nothing";   // s evaluates to "nothing"

The last line is equivalent to: 

string s = (sb == null ? "nothing" : sb.ToString());

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