CODEWITHSUNDEEP
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MrM
MrM

Reputation: 21999

.ToString(), (string), or as String. When to use what?

I ran into a bug that was bothering me. I had JObject that I thought would be fine with 

obj["role"].ToString()

The string was there and everything. A final resort was to change to a 

(string)obj["role"]

just to see what happens and it works. My question is how do I know when to use a .ToString() as opposed to a (string) as opposed to an "as String".

Upvotes: 10

Views: 4372

Answers (3)

Kirk Woll
Kirk Woll

Reputation: 77576

It shouldn't make a difference in your example. The only scenario where it would make a difference is if there is user-type-conversion (to a string) defined on whatever type obj["role"] is. In that case it's possibly that the cast to a string changed it to a different object, upon which the .ToString() was implemented differently.

Upvotes: 0

Darin Dimitrov
Darin Dimitrov

Reputation: 1039120

(string) casts the instance to string and it might throw an exception at runtime if the object you are trying to cast is not a string. The as operator also tries to cast but it doesn't throw an exception if the instance is not a string but returns null. And the ToString method of course comes from System.Object so it will depend on whether tyhe underlying type has overridden it.

Upvotes: 2

jason
jason

Reputation: 241701

If the object is a string, or there is an explicit cast operator to (string), then it is okay to say

string s = (string)obj["role"];

Otherwise, this will give you an InvalidCastException.

Note that here you could say

string s = obj["role"] as String;

which will set s to null if obj["role"] is not an instance of string. Note that for as, explicit cast operators are ignored.

If obj["role"] is neither a string nor an instance of a class that has an explicit cast operator to string, you have to say 

string s = obj["role"].ToString();

But be careful, the latter can throw a NullReferenceException.

Upvotes: 21

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