Formik Patterns

Basic Form Setup

const validationSchema = yup.object({
  email: yup.string().email('Invalid email').required('Email is required'),
  password: yup.string().min(8, 'Min 8 characters').required('Password is required'),
});

const LoginForm = () => {
  const formik = useFormik({
    initialValues: {
      email: '',
      password: '',
    },
    validationSchema,
    onSubmit: async (values) => {
      await loginMutation({ variables: { input: values } });
    },
  });

  return (
    
      

      

      
        Login
      
    
  );
};

Validation Schemas

Common Patterns

// Email
email: yup.string()
  .email('Invalid email address')
  .required('Email is required')

// Password with requirements
password: yup.string()
  .min(8, 'Must be at least 8 characters')
  .matches(/[a-z]/, 'Must contain lowercase letter')
  .matches(/[A-Z]/, 'Must contain uppercase letter')
  .matches(/[0-9]/, 'Must contain number')
  .required('Password is required')

// Confirm password
confirmPassword: yup.string()
  .oneOf([yup.ref('password')], 'Passwords must match')
  .required('Please confirm password')

// Phone number
phone: yup.string()
  .matches(/^\\+?[1-9]\\d{1,14}$/, 'Invalid phone number')
  .required('Phone is required')

// Optional field with validation when present
website: yup.string()
  .url('Must be a valid URL')
  .nullable()

// Number with range
quantity: yup.number()
  .min(1, 'Minimum 1')
  .max(100, 'Maximum 100')
  .required('Quantity required')

// Array with minimum items
tags: yup.array()
  .of(yup.string())
  .min(1, 'Select at least one tag')

Conditional Validation

const schema = yup.object({
  hasCompany: yup.boolean(),
  companyName: yup.string().when('hasCompany', {
    is: true,
    then: (schema) => schema.required('Company name required'),
    otherwise: (schema) => schema.nullable(),
  }),
});

Form Field Helpers

Input Helper

const getFieldProps = (name: keyof typeof formik.values) => ({
  value: formik.values[name],
  onChangeText: formik.handleChange(name),
  onBlur: formik.handleBlur(name),
  error: formik.touched[name] ? formik.errors[name] : undefined,
});

// Usage

Select/Picker Helper

 formik.setFieldValue('country', value)}
  error={formik.touched.country ? formik.errors.country : undefined}
  options={countryOptions}
/>

Form Submission with GraphQL

const CreateItemForm = () => {
  const [createItem] = useCreateItemMutation({
    onCompleted: () => {
      toast.success({ title: 'Item created' });
      navigation.goBack();
    },
    onError: (error) => {
      console.error('createItem failed:', error);
      toast.error({ title: 'Failed to create item' });
    },
  });

  const formik = useFormik({
    initialValues: { name: '', description: '' },
    validationSchema,
    onSubmit: async (values, { setSubmitting }) => {
      try {
        await createItem({ variables: { input: values } });
      } finally {
        setSubmitting(false);
      }
    },
  });

  return (
    
      
      
        Create
      
    
  );
};

Edit Form with Initial Values

const EditItemForm = ({ item }: { item: Item }) => {
  const [updateItem] = useUpdateItemMutation({
    onCompleted: () => toast.success({ title: 'Saved' }),
    onError: (error) => {
      console.error('updateItem failed:', error);
      toast.error({ title: 'Save failed' });
    },
  });

  const formik = useFormik({
    initialValues: {
      name: item.name,
      description: item.description ?? '',
    },
    enableReinitialize: true, // Update when item prop changes
    validationSchema,
    onSubmit: async (values) => {
      await updateItem({
        variables: { id: item.id, input: values },
      });
    },
  });

  // Track if form has changes
  const hasChanges = formik.dirty;

  return (
    
      
      
        Save Changes
      
    
  );
};

Form State Helpers

const {
  values,          // Current form values
  errors,          // Validation errors
  touched,         // Fields that have been touched
  isValid,         // Form passes validation
  isSubmitting,    // Submit in progress
  dirty,           // Values differ from initial
  handleSubmit,    // Submit handler
  handleChange,    // Change handler
  handleBlur,      // Blur handler
  setFieldValue,   // Set single field
  setFieldTouched, // Mark field touched
  resetForm,       // Reset to initial values
  setSubmitting,   // Control submitting state
} = formik;

Multi-Step Forms

const MultiStepForm = () => {
  const [step, setStep] = useState(0);

  const formik = useFormik({
    initialValues: {
      // Step 1
      name: '',
      email: '',
      // Step 2
      address: '',
      city: '',
      // Step 3
      cardNumber: '',
    },
    validationSchema: stepSchemas[step],
    onSubmit: async (values) => {
      if (step < steps.length - 1) {
        setStep(step + 1);
      } else {
        await submitOrder(values);
      }
    },
  });

  return (
    
      {step === 0 && }
      {step === 1 && }
      {step === 2 && }

      
        {step > 0 && (
           setStep(step - 1)}>
            Back
          
        )}
        
          {step < steps.length - 1 ? 'Next' : 'Submit'}
        
      
    
  );
};

Anti-Patterns

// WRONG - Not showing validation errors

// CORRECT - Show errors when touched

// WRONG - Submit button always enabled
Submit

// CORRECT - Disabled when invalid or submitting

  Submit

// WRONG - No error handling on mutation
onSubmit: async (values) => {
  await createItem({ variables: { input: values } });
}

// CORRECT - Handle errors
onSubmit: async (values, { setSubmitting }) => {
  try {
    await createItem({ variables: { input: values } });
  } catch (error) {
    toast.error({ title: 'Failed to save' });
  } finally {
    setSubmitting(false);
  }
}

Integration with Other Skills

• graphql-schema: Mutation submission patterns
• react-ui-patterns: Loading/error states
• testing-patterns: Test form validation and submission