How to do null/empty check of a String inside a TextFormField validator function in dart/flutter?

Question

Is there a shorter way to check if a string is either null or empty? Do I need to write every time 2 conditions inside if to check it?

validator: (value) {
    if (value == null || value.isEmpty){
        //....
    }
}

In python we can do if value and it works. In javascript we could do if(!value).

score 1 · Accepted Answer · answered Sep 13 '22 at 18:21

1

As from my understanding, the TextEditingController use TextEditingValue.empty which is providing empty string initially. I am not able to get null exception.

I think we can use ! while we are sure the value is empty, not null.

validator: (value) {
  if (value!.isEmpty) return "Empty";

I always prefer checking null first, for nullable data type.

answered Sep 13 '22 at 18:21

Md. Yeasin Sheikh

54,221
7
29
56

1

you can also create custom extension on String – Md. Yeasin Sheikh Sep 13 '22 at 18:27
Does this mean validator wont run if there is no value since you are using ! What if I click on a text field and do nothing and click on other text field. Does the value become '' or null? – Ramsudharsan Manoharan Sep 13 '22 at 18:49
1

I tried it. It will provide '' empty string and not null. But the point is we are forced to do a null check using ! even if the validator always gives empty string. I'll accept this answer for now. – Ramsudharsan Manoharan Sep 13 '22 at 19:07

score 0 · Answer 2 · answered Sep 13 '22 at 18:52

0

try this

validator: (value) {
if (value.isNotEmpty){
     print(value);
 }else{
   print("Empty");
 }
}

answered Sep 13 '22 at 18:52

Kundan mandal

73
4

Same issue as .isEmpty: The property 'isNotEmpty' can't be unconditionally accessed because the receiver can be 'null'. Im forced to do a null check. – Ramsudharsan Manoharan Sep 13 '22 at 19:03

score 0 · Answer 3 · answered Jul 18 '23 at 06:46

do a guard check

validator: (String? value) {
  if (value?.isNotEmpty == true) {
    return null;
  }
  
  return 'Value cannot be null or empty';
},

this will do, because the combination of ?. and == true will check for null.

while the .isNotEmpty checks as the method's usage, if not empty.

How to do null/empty check of a String inside a TextFormField validator function in dart/flutter?

3 Answers3