CODEWITHSUNDEEP
flutterdart
Chunsheng Wei
Chunsheng Wei

Reputation: 961

How to check a string null in Dart?

How do you check a string for "null" in Dart? (not a null object)

is there some Dart SDK API like Java's equals?

Upvotes: 4

Views: 11544

Answers (5)

Michael Codes
Michael Codes

Reputation: 135

Most of the time the application does not work especially when you are using Future<String> return type
the below code seems to work

myString == "null";
myFinalString = ["", null, "null", "\"null\""].contains(myString);
print(myFinalString)
Output: =>true

Upvotes: -1

Suragch
Suragch

Reputation: 512824

In addition to

myString == 'null'

or

myString == null

There is another meaning that "null" could take: the null character. In ASCII or Unicode this has the code value of 0. So you could check for this value like so:

myString == '\u0000'

or

myString.codeUnits.first == 0

Upvotes: 1

madhead
madhead

Reputation: 33511

Checking if the string is null:

if (s == null) {
    …
}

Checking if the string is not null:

if (s != null) {
    …
}

Returning the string if not null, 'other value' otherwise:

return s ?? 'other value'

Assigning a value to the string only if that string is null:

s ??= 'value'

Calling a method (property) on the string if it's not null

s?.length

Upvotes: 4

neohaojun
neohaojun

Reputation: 312

You can use the isEmpty property.

bool [string name] isEmpty;

Alternatively, you can do this:

String text = "text"; 
print(text.isEmpty);

Output: false

Edit: I believe that Mohammad Assad Arshad's answer is more accurate. Sorry about that.

Upvotes: 1

Mohammad Assad Arshad
Mohammad Assad Arshad

Reputation: 1784

I believe isEmpty property will return false since if your string is null, it still holds an object and won't be empty. So depending on what you mean in your post.

If you want to check for the string 'null', just do 

if (stringVar == 'null')

or if you want to check if your string is null, then

if (stringVar == null)

Upvotes: 7

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