How can I implement custom validation in React Native?

How can I implement custom validation in React Native?

You can create custom validation in React Native by using libraries like Formik or by implementing your own validation logic.

Can you show me an example of using Formik for validation?

Sure! Here's a simple example using Formik with a custom validation function:

import React from 'react';
import { Formik } from 'formik';
import * as Yup from 'yup';

const validationSchema = Yup.object().shape({
  email: Yup.string().email('Invalid email').required('Required'),
});

const MyForm = () => (
  <Formik
    initialValues={{ email: '' }}
    validationSchema={validationSchema}
    onSubmit={values => { console.log(values); }}
  >
    {({ handleChange, handleSubmit, values, errors }) => (
      <>
        <input
          type="text"
          onChange={handleChange('email')}
          value={values.email}
        />
        {errors.email && <Text>{errors.email}</Text>}
        <Button onPress={handleSubmit} title="Submit" />
      </>
    )}
  </Formik>
);

This will validate the email field.

What if I want to add more fields with different validation rules?

You can extend the validationSchema by adding more fields with their respective validation rules. For example:

const validationSchema = Yup.object().shape({
  email: Yup.string().email('Invalid email').required('Required'),
  password: Yup.string().min(6, 'Password too short').required('Required'),
});

Just make sure to include the corresponding input fields in your form.