In this post, we will do a simple example to check if a String is a number.

1. Use tryParse method:

bool isNumericUsing_tryParse(String string) {
  // Null or empty string is not a number
  if (string == null || string.isEmpty) {
    return false;
  }

  // Try to parse input string to number. 
  // Both integer and double work.
  // Use int.tryParse if you want to check integer only.
  // Use double.tryParse if you want to check double only.
  final number = num.tryParse(string);

  if (number == null) {
    return false;
  }

  return true;
}

2. Use RegExp (Regular Expression)

bool isNumericUsingRegularExpression(String string) {
  final numericRegex = 
    RegExp(r'^-?(([0-9]*)|(([0-9]*)\.([0-9]*)))$');

  return numericRegex.hasMatch(string);
}

Test it!

void main() {
  print(isNumericUsing_tryParse('12345')); // true
  print(isNumericUsing_tryParse('12345a')); // false
  print(isNumericUsing_tryParse('012345')); // true
  print(isNumericUsing_tryParse('-12345')); // true
  print(isNumericUsing_tryParse('1.23')); // true
  print(isNumericUsing_tryParse('1.23f')); // false

  print('---');

  print(isNumericUsingRegularExpression('12345')); // true
  print(isNumericUsingRegularExpression('12345a')); // false
  print(isNumericUsingRegularExpression('012345')); // true
  print(isNumericUsingRegularExpression('-12345')); // true
  print(isNumericUsingRegularExpression('1.23')); // true
  print(isNumericUsingRegularExpression('1.23f')); // false
}

If you are looking for mobile/web Software Engineers to build you next projects, please Drop us your request!

Phuc Tran

Creator of Coflutter.
Daddy at home.
Building education apps!
Follow him on Twitter, Github, StackOverflow, LinkedIn, Upwork.