CODEWITHSUNDEEP
c#
frenchie
frenchie

Reputation: 51947

.Trim() when string is empty or null

I'm receiving some data from the client in the form of json. I'm writing this:

string TheText; // or whould it be better string TheText = ""; ?
TheText = ((serializer.ConvertToType<string>(dictionary["TheText"])).Trim());

If the variable that's being parsed from json comes back empty, does this code crash when I call the .Trim() method?

Thanks.

Upvotes: 36

Views: 113354

Answers (9)

TcKs
TcKs

Reputation: 26632

You can use elvis operator, also known as "null-conditional-operators":

GetNullableString()?.Trim(); // returns NULL or trimmed string

More info: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators

Upvotes: 44

Ioan Costea
Ioan Costea

Reputation: 11

Recently I had to check a string if it is null, empty or whitespace using just one if condition and for that I found out that you can add "" to a null string to make it non null.

string test = GetStringFromSomeWhere(); // null
if(string.IsNullOrEmpty(test.Trim())) { return true; } // Exception

So I did this instead

string test = GetStringFromSomeWhere() + ""; // ""
if(string.IsNullOrEmpty(test.Trim())) { return true; } // true

Upvotes: 1

Ry-
Ry-

Reputation: 224963

  • No, it would not be better to initialize TheText to "". You're assigning to it right afterwards.

  • No, it won't crash – Trim() works just fine on an empty string. If by "empty" you mean that it can be null, then yes, it will crash; you could have null remain null with a null-conditional call:

    string TheText =
    serializer.ConvertToType<string>(dictionary["TheText"])?.Trim();

Upvotes: 6

Jpsy
Jpsy

Reputation: 20862

Some basic techniques to check strings against null before you trim:

  • (mystring ?? "").Trim()
    The "null coalescing operator" ?? will return the first operand. Only when this operand is null, the second operand will be returned (as a kind of default value).
    The above example will return an empty string if mystring is null.
  • mystring?.Trim()
    The "null conditional operator" ? will short cirtuit a chain of operations in dot-notation. If the operand is null, the following operations will not be executed and null will be returned.
    The above example will return null if mystring is null.
  • if( string.IsNullOrWhiteSpace(mystring) ) { ... }
    the IsNullOrWhiteSpace() method may replace trimming if you actually want to check if there is real content in mystring. It returns true if the operand is null, empty, or nothing but whitespace characters.

Upvotes: 18

Trần Quốc Triển
Trần Quốc Triển

Reputation: 1

You can use this code as beblow

 string theText = (((serializer.ConvertToType<string>(dictionary["TheText"])))+ string.Empty).Trim();

Upvotes: 0

shanabus
shanabus

Reputation: 13115

As suggested in some of the comments, you may now use c# 6 Null-conditional operators with this syntax:

string TheText = (serializer.ConvertToType<string>(dictionary["TheText"]))?.Trim();

Documentation: https://msdn.microsoft.com/en-us/library/dn986595.aspx

Upvotes: 6

JsonStatham
JsonStatham

Reputation: 10374

If you have a few fields you wish to trim but your getting exceptions for those records that have nulls in certain fields, then writing a quick extension method will be the easiest method:

public static class ExtensionMethods
    {
        public static string TrimIfNotNull(this string value)
        {
            if (value != null)
            {
                return value.Trim();
            }
            return null;
        }
    }

Sample example of use:

string concatenated = String.Format("{0} {1} {2}", myObject.fieldOne.TrimIfNotNull(), myObject.fieldTwo.TrimIfNotNull(), myObject.fieldThree.TrimIfNotNull());

Upvotes: 16

Armen Tsirunyan
Armen Tsirunyan

Reputation: 133024

Calling Trim() on an empty string will result in an empty string. Calling Trim() on null will throw NullReferenceException

Upvotes: 18

Oded
Oded

Reputation: 499072

If the serializer returns an empty string, Trim will do nothing.

If the serializer returns null, you will get a NullReferenceException on the call to Trim.

Your code would be better written (as far as initialization is concerned) like this:

string theText = 
            ((serializer.ConvertToType<string>(dictionary["TheText"])).Trim());

There is no point in declaring and initializing the variable and the immediately assigning to it.

The following would be safest, if you don't know what the serializer might return:

string theText = ((serializer.ConvertToType<string>(dictionary["TheText"])));

if(!string.IsNullOrEmpty(theText))
{
    theText = theText.Trim();
}

Upvotes: 27

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