How to Format an Interploated String In Flutter ?

• General

Earlier we have been through How to find Difference Between Two Dates In Flutter. So this time we will try something new like How to Format an Interpolated String In Flutter.

Let move ahead with it.

How to Format an Interpolated String In Flutter?

Dart supports string interpolation. Consider a code snippet as below:

var seconds = 5;
print("Send $seconds seconds ago");

var harryLikes = 'Silvia';
var otherName = 'Erik';
var otherLikes = 'Chess';
print("Harry like $harryLikes");
print("I think $otherName like $otherLikes");

Also, more complex expressions can be embedded with ${…}

print('Calc 3 + 5 = ${3 + 5}');

The number of types and the intl package provide more methods to format numbers and dates.

You can also try the below examples:

• NumberFormat Class
• Currency format in dart

You can also try the below way:

• Add the following to your pubspec.yaml

  dependencies:
    sprintf: "^4.0.0"

  then run pub install.

  Next, import dart-sprintf:

import 'package:sprintf/sprintf.dart';

void main() {
     double seconds = 5.0;
       String name = 'Dilki';
       List<String> pets = ['Cats', 'Dogs'];

       String sentence1 = sprintf('Sends %2.2f seconds ago.', [seconds]);
       String sentence2 = sprintf('Harry likes %s, I think %s likes %s.', [pets[0], name, pets[1]]);

       print(sentence1);
       print(sentence2);
}

The output will look like the below : 

Sends 5.00 seconds ago.
Harry likes Cats, I think Dilki likes Dogs.

If you want String interpolation similar to Android Today is %1$ and tomorrow is %2$, you can create a top-level function or an extension that can do something similar. In this instance, I keep it similar to Android strings as I’m currently porting an Android app.

Top Level Function

String interpolate(String string, List<String> params) {

  String result = string;
  for (int i = 1; i < params.length + 1; i++) {
    result = result.replaceAll('%${i}\$', params[i-1]);
  }

  return result;
}

You can then call interpolate(STRING_TO_INTERPOLATE, LIST_OF_STRINGS) and your string would be interpolated.

Extensions

You can create an extension function that does something similar to Android String.format()

extension StringExtension on String {
    String format(List<String> params) => interpolate(this, params);
}

This would then allow you to call text.format(placeHolders)

Testing

test('String.format extension works', () {
    // Given
    const String text = 'Today is %1\$ and tomorrow is %2\$';
    final List<String> placeHolders = List<String>()..add('Monday')..add('Tuesday');
    const String expected = 'Today is Monday and tomorrow is Tuesday';

    // When
    final String actual = text.format(placeHolders);

    // Then
    expect(actual, expected);
  })

So you could also have something simple like this:

• Usage

  interpolate('Hello {#}{#}, cool {#}',['world','!','?']);
  // Hello world!, cool ?

• Function

  static const needleRegex = r'{#}';
  static const needle = '{#}';
  static final RegExp exp = new RegExp(needleRegex);
  
  static String interpolate(String string, List l) {
    Iterable<RegExpMatch> matches = exp.allMatches(string);
  
    assert(l.length == matches.length);
  
    var i = -1;
    return string.replaceAllMapped(exp, (match) {
      print(match.group(0));
      i = i + 1;
      return '${l[i]}';
    });
  }

Conclusion:

Thanks for Reading. Hope you have enjoyed it.

So in this article, we have been through How to Format an Interpolated String In Flutter.

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Written by Abhishek Dhanani

Abhishek Dhanani, a skilled software developer with 3+ years of experience, masters Dart, JavaScript, TypeScript, and frameworks like Flutter and NodeJS. Proficient in MySQL, Firebase, and cloud platforms AWS and GCP, he delivers innovative digital solutions.