How to handle null exception when converting from object to string?

Question

Just curious:

These lines throw Invalid Cast Exception: Unable to cast object of type 'System.Double' to type 'System.String'.

 Object obj = new object();
 obj = 20.09089;
 string value = (string)obj;

I receive the obj value from a library.

How to simply convert to string when we don't know the type of object while enumerating?

In addition to the answers, note that there's a difference between (string)obj and obj.ToString()... — James Thorpe
– James Thorpe, Commented Nov 24, 2014 at 13:41
@SriramSakthivel - In this case, yes. But since there is "null exception" in the title, one might also have to take into account that obj could be null. — Corak
– Corak, Commented Nov 24, 2014 at 13:45
Btw. if you don't know the exact type, but are certain, that it can only be one of a handfull of known types, you could check that with is/as. if (obj is double) { \\ do double stuff } — Corak
– Corak, Commented Nov 24, 2014 at 13:50
Convert.ToString() does the same thing in the end. But it also checks if the given object implements IConvertible or IFormattable beforehand (and calls the more appropriate ToString methods if they do). So if you want those checks, or at least can live with them, then go for it. Yackov just showed the way with possibly the smallest footprint while still being safe. — Corak
– Corak, Commented Nov 25, 2014 at 7:17

ymz · Accepted Answer · 2014-11-24 13:41:06Z

5

that is why every object in .net has the ToString() method (inherited from Object)

string str = (obj == null) ? string.Empty : obj.ToString();

answered Nov 24, 2014 at 13:41

ymz

6,9641 gold badge26 silver badges41 bronze badges

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

1 Comment

now he who must not be named. Over a year ago

Great answer. BTW, I am now using Convert.ToString() instead of .ToString() since the former can handle null values too :)

Soner Gönül · Accepted Answer · 2014-11-24 13:57:34Z

2

This is an boxing / unboxing issue.

20.09089 is a double by default. When you wanna unbox a primitive type from object, you need to unbox it the original type first.

Object obj = new object();
obj = 20.09089;
string value = ((double)obj).ToString();

or simplify;

Object obj = new object();
obj = 20.09089;
string value = obj.ToString();

edited Nov 24, 2014 at 13:57

answered Nov 24, 2014 at 13:38

Soner Gönül

99.1k103 gold badges224 silver badges375 bronze badges

2 Comments

Sriram Sakthivel Over a year ago

That is superfluous, simply use obj.ToString

Soner Gönül Over a year ago

@SriramSakthivel That's right. I just want to point why OP can't cast directly to string as (string)obj in my answer instead of how to get it's string representation. But I added to my answer. Thanks.

Collectives™ on Stack Overflow

How to handle null exception when converting from object to string?

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related