Check If A String Contains Only Letters In Dart

Dart is a powerful language now more popular with the advent of Flutter, a framework utilized for building cross-platform applications. This article will guide you through one of the basic yet essential String related tasks in Dart: verifying if a String contains only letters.

Code snippet for Checking if a String Contains Only Letters

The below code snippet demonstrates how to check if a string is composed of only letters in Dart:

bool isStringOnlyLetters(String str) {
  return str.trim().isNotEmpty && str.split('').every((char) => RegExp(r'^[a-zA-Z]+$').hasMatch(char));
}

void main() {
  print(isStringOnlyLetters('hello'));  // returns: true
  print(isStringOnlyLetters('hello2')); // returns: false
}

Code Explanation for Checking if a String Contains Only Letters

Let’s break down each part of the code to understand how it works:

1. Firstly, the function isStringOnlyLetters is defined which takes a string parameter. This function will be used to check if all characters of the string are letters.

2. Inside the function, the Dart trim() function is used which removes all whitespace at the beginning and at the end of the string. isNotEmpty then checks if the trimmed String is not empty.

3. The string is then split into a List of individual characters using split('').

4. The every method is used on the List of characters which takes a function that tests each character. If the function returns true for every character, then the every method also returns true.

5. Inside the every method, a pattern for only lower case and upper case English alphabets is defined using RegExp(r'^[a-zA-Z]+$'). hasMatch is then used on each character to verify if it matches the pattern. If it matches, it returns true.

6. The function isStringOnlyLetters therefore checks if every character of a string is an English letter and returns true only when all characters are letters.

7. In the main function, the isStringOnlyLetters function is called with a couple of different strings and the return value is printed. The return value is true when the string contains only English letters and false if there are any other characters.