maxLength static method

FormFieldValidator<String> maxLength(int maxLength, String errorMessage)

Validator that requires the length of the field's value to be less than or equal to the provided maximum length.

Validate that the field has maximum of 5 characters

          TextFormField(
           decoration: InputDecoration(
             labelText: 'Maximum length 5',
           ),
           validator: Validators.maxLength(5, 'Characters are greater than 5'),
         ),

Implementation

static FormFieldValidator<String> maxLength(
    int maxLength, String errorMessage) {
  return (value) {
    if (value == null) {
      value = '';
    }
    if (value.isEmpty) return null;

    if (value.length > maxLength)
      return errorMessage;
    else
      return null;
  };
}