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How to validate textform field for special characters when it can be null in flutter?

I want to validate textformfield for special characters but it can also be null, For Example: Middle name: Not every one has middle name so it can be null but for those who have middle name it has to be alphabets not special characters. How do i do it?

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2

Answers


  1. 0

    Example

    final RegExp _alphabetRegex = RegExp(r'^[a-zA-Z]+$');

TextFormField(
  decoration: InputDecoration(labelText: 'Middle name'),
  validator: (value) {
    if (value == null || value.isEmpty) {
      return null; // Return null if the value is empty or null
    } else if (!_alphabetRegex.hasMatch(value)) {
      return 'Middle name can only contain alphabets'; // Return an error message if the value contains special characters
    }
    return null; // Return null if the value is valid
  },
);
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  2. 0

    To validate a TextFormField for special characters but also allow it to be null, you can use a RegExp pattern in combination with the validator parameter of the TextFormField.

    Here’s an example:

    TextFormField(
  decoration: InputDecoration(
    labelText: 'Middle Name',
  ),
  validator: (value) {
    if (value == null || value.isEmpty) {
      // Allow null or empty values
      return null;
    }
    // Use a RegExp pattern to match only alphabets
    final pattern = RegExp(r'^[a-zA-Z]+$');
    if (!pattern.hasMatch(value)) {
      return 'Middle name should contain only alphabets';
    }
    return null;
  },
),

    • In this example, the validator parameter is used to define a function that takes the value of the TextFormField as input and returns an error message if the value is not valid. If the value is null or empty, the function returns null to indicate that the value is valid.

    • If the value is not null or empty, the function uses a RegExp pattern to match only alphabets. The pattern r’^[a-zA-Z]+$’ matches only strings that contain one or more alphabets, and the hasMatch() method of the RegExp class is used to check if the value matches the pattern.

    • If the value does not match the pattern, the function returns an error message indicating that the middle name should contain only alphabets.

    • By using this approach, you can validate a TextFormField for special characters while also allowing it to be null.

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