Why doesn't this ?: operator return null?

Question

I wrote this line of code to handle nulls but I still get an "Object reference not set to an instance of an object" error whenever I run this line of code when expectedItem is null. What gives? What's the proper way to write this? Since expectedItem is null, I'd expect expectedItem.ExpectedResultAmount to be null also so this statement should assign an empty string to x.

string x = expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "";

zerkms · Accepted Answer · 2012-08-28 23:23:20Z

3

You need to check if expectedItem is not null, not its property

string x = expectedItem != null ? expectedItem.ExpectedResultAmount : "";

answered Aug 28, 2012 at 23:23

zerkms

256k73 gold badges447 silver badges551 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Matthew Layton Over a year ago

should the op not check both the object instance and its property? see my answer.

zerkms Over a year ago

@activwerx: if they should - they will find this out soon ;-) Doing mistakes is the best way to learn

Matthew Layton · Accepted Answer · 2012-08-28 23:32:21Z

1

You should check both the object instance (expectedItem) and the property (expectedItem.ExpectedResultAmount) as either may fail:

string x = expectedItem != null && expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "";

answered Aug 28, 2012 at 23:32

Matthew Layton

42.9k59 gold badges213 silver badges346 bronze badges

6 Comments

starvingPhilosopher Over a year ago

I'm picking this one because it checks both the object and its property and I like this syntax style

FlavorScape Over a year ago

really? I find reading multiple nested ternary operators hard on the eyes.

Matthew Layton Over a year ago

@FlavorScape, I agree, but I wrote it in the same fashion as the OP posted in the question.

starvingPhilosopher Over a year ago

@FlavorScape, Which of the styles in the answers would you use or do you have a specific style to share? Thanks in advance

starvingPhilosopher Over a year ago

@activwerx Which of the styles in the answers would you use or do you have a specific style to share? Thanks in advance

|

D Stanley · Accepted Answer · 2012-08-28 23:23:45Z

1

Your expectation is wrong. try

string x = expectedItem == null ? "" : expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "";

answered Aug 28, 2012 at 23:23

D Stanley

153k12 gold badges189 silver badges257 bronze badges

1 Comment

psubsee2003 Over a year ago

+1 same as the selected answer, and you were first by several minutes

Simon Whitehead · Accepted Answer · 2012-08-28 23:23:48Z

1

expcetedItem is no doubt null:

string x;

if (expectedItem != null)
    x = expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "";

answered Aug 28, 2012 at 23:23

Simon Whitehead

65.3k10 gold badges120 silver badges140 bronze badges

Comments

Adam Mihalcin · Accepted Answer · 2012-08-28 23:24:06Z

1

The short answer: you're dereferencing expectedItem because you're checking expectedItem.ExpectedResultAmount for null rather than checking expectedItem itself. You should probably write

string x = expectedItem != null ? expectedItem.ExpectedResultAmount : "";

answered Aug 28, 2012 at 23:24

Adam Mihalcin

14.5k4 gold badges39 silver badges53 bronze badges

Comments

FlavorScape · Accepted Answer · 2012-08-28 23:29:43Z

0

expectedItem is null.

if( expectedItem != null)
  x = expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "";
else 
  x = "poop";

edited Aug 28, 2012 at 23:29

answered Aug 28, 2012 at 23:24

FlavorScape

14.5k13 gold badges79 silver badges124 bronze badges

1 Comment

Robert Harvey Over a year ago

You can't say if (expecteditem) in C#; you have to explicitly compare it to null.

Nicodemeus · Accepted Answer · 2012-08-28 23:30:24Z

0

Try this

string x = expectedItem != null && expectedItem.ExpectedResultAmount != null
    ? expectedItem.ExpectedResultAmount
    : string.Empty;

answered Aug 28, 2012 at 23:30

Nicodemeus

4,08322 silver badges23 bronze badges

Comments

Lele · Accepted Answer · 2012-08-29 10:44:29Z

0

The right way to write your code is as follows:

string x = expectedItem != null ? (expectedItem.ExpectedResultAmount != null ? expectedItem.ExpectedResultAmount : "") : "";

You first have to make sure expectedItem is not null, if it is you would have an illegal operation called null pointer; you should then assign x an empty string.

If it is not null, and you write it like this

string x = expectedItem != null ? expectedItem.ExpectedResultAmount : "";

x could be either null or expectedItem.ExpectedResultAmount, if you don't want x to be null, for instance, you would make string operations on it later such as Compare or Concat, you should also make sure its member ExpectedResultAmount is not null either.

edited Aug 29, 2012 at 10:44

answered Aug 28, 2012 at 23:43

Lele

12 bronze badges

Comments

Matthew Layton · Accepted Answer · 2012-08-30 19:33:45Z

0

As it has been suggested the the accepted answer is "not easy on the eye", you might also consider this:

string x = ""; //string is empty...
if (expectedItem != null && expectedItem.ExpectedResultAmount != null)
{
    x = expectedItem.ExpectedResultAmount; //...unless this exists.
}

answered Aug 30, 2012 at 19:33

Matthew Layton

42.9k59 gold badges213 silver badges346 bronze badges

1 Comment

Matthew Layton Over a year ago

It may be a 5 line (as opposed to my 1 line) solution, but it's very easy to read!

Collectives™ on Stack Overflow

Why doesn't this ?: operator return null?

9 Answers 9

2 Comments

6 Comments

1 Comment

Comments

Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

9 Answers 9

2 Comments

6 Comments

1 Comment

Comments

Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related