rephrase the if statement in Dart 2.0 using null

Question

I have following statement in flutter. weight is the text from _weightController i.e. _weightController.text

int.parse(weight).toString().isNotEmpty && int.parse(weight) > 0

But in Dart 2.0 it is not working properly. For empty TextField, it is giving the error.

====== Exception caught by gesture ==============================
The following FormatException was thrown while handling a gesture: 
Invalid number (at character 1)

The code block is like this.

if (int.parse(weight).toString().isNotEmpty && int.parse(weight) > 0)
    return int.parse(weight) * multiplier;
  else
    print('Error');

Naslausky · Accepted Answer · 2020-04-09 15:18:41Z

1

As an alternative to the other answer, you can use the tryParse() method:

Like parse except that this function returns null where a similar call to parse would throw a FormatException, and the source must still not be null.

If you use this approach, you should check the return value for null:

String weight ="";
int number = int.tryParse(weight);
if (number !=null){
  print(number );
}
else
  print("error");

Don't forget to also check the variable for null with weight ? "" or with weight != null

edited Apr 9, 2020 at 15:18

answered Apr 9, 2020 at 15:11

Naslausky

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2 Comments

GoharSahi Over a year ago

This worked for me. if (int.tryParse(weight) != null && int.tryParse(weight) > 0). Thanks. I also need to check for 0.

Sidak Over a year ago

You mean weight ?? " ", Not single ?

CopsOnRoad · Accepted Answer · 2020-04-11 06:53:45Z

1

Try this:

if (weight != null && weight.isNotEmpty) {
  return int.tryParse(weight) * multiplier;
} else {
  print("CoolTag: error");
  return -1;
}

edited Apr 11, 2020 at 6:53

answered Apr 9, 2020 at 12:16

CopsOnRoad

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2 Comments

GoharSahi Over a year ago

This worked partially though. I had to also check for 0 which was giving error. I used int.tryParse(weight) > 0 and that worked for me.

CopsOnRoad Over a year ago

Ok, but the accepted answer doesn't cover all the cases, which mine does.

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