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react-hook-form mit Controller einrichten

react-hook-form mit Controller einrichten ist eine kostenlose React Native Academy-Lektion auf CoddyKit. Dies ist Lektion 1 von 4. Du kannst die komplette Lektion unten kostenlos lesen – dann übst du sie direkt im Browser mit einem integrierten Code-Editor und einem KI-Tutor rund um die Uhr. Sie ist Teil des React Native Academy-Lernpfads, und dein Fortschritt wird über Web und CoddyKit-App synchronisiert. Der React Native Academy-Kurs umfasst insgesamt 4 Lektionen.

Teile dieser Lektion wurden noch nicht übersetzt und werden auf Englisch angezeigt.

Why react-hook-form?

react-hook-form is a performant, flexible library for building forms in React and React Native. Unlike manually wiring every input to useState, react-hook-form uses uncontrolled inputs to minimize re-renders. It integrates validation, error handling, and form submission into a single coherent API, and it works seamlessly with any UI component library through the Controller wrapper.

Installing react-hook-form

Install react-hook-form from npm. It has no dependencies and works with any React version 16.8+. No special configuration is needed — import its hooks and components directly into your React Native components after installation.

npm install react-hook-form

Creating a Form Instance with useForm

Call useForm() at the top of your component to create a form instance. It returns several utilities: control (for wiring inputs via Controller), handleSubmit (for form submission), formState.errors (for displaying validation errors), and reset (to clear all fields). Pass default values to useForm to pre-populate the form.

import { useForm } from 'react-hook-form';

interface LoginForm {
  email: string;
  password: string;
}

export default function LoginScreen() {
  const {
    control,
    handleSubmit,
    formState: { errors },
    reset,
  } = useForm<LoginForm>({
    defaultValues: { email: '', password: '' },
  });
}

Wrapping TextInput with Controller

In React Native, inputs are controlled components that need to be wrapped in Controller so react-hook-form can manage their values. Pass the control object, the field name, and a render prop. The render prop receives field which contains value, onChange, and onBlur to wire to the TextInput.

import { Controller } from 'react-hook-form';

<Controller
  control={control}
  name='email'
  render={({ field: { onChange, onBlur, value } }) => (
    <TextInput
      value={value}
      onChangeText={onChange}
      onBlur={onBlur}
      placeholder='Email'
      keyboardType='email-address'
      autoCapitalize='none'
    />
  )}
/>

Adding Validation Rules

Pass a rules prop to Controller to define validation constraints. The required rule marks a field as mandatory, minLength enforces a minimum character count, maxLength caps input length, and pattern validates against a regex. Each rule takes an object with a value and a message string shown when the rule fails.

<Controller
  control={control}
  name='email'
  rules={{
    required: { value: true, message: 'Email is required' },
    pattern: {
      value: /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/,
      message: 'Enter a valid email address',
    },
  }}
  render={({ field: { onChange, onBlur, value } }) => (
    <TextInput value={value} onChangeText={onChange} onBlur={onBlur} />
  )}
/>

Displaying Field Errors

After Controller validates a field, any error is available in formState.errors[fieldName]. Access its message property and render it below the input in a red Text component. Errors only appear after the field has been touched (onBlur) or after the first submit attempt, preventing premature error messages.

<Controller
  control={control}
  name='email'
  rules={{ required: 'Email is required' }}
  render={({ field: { onChange, onBlur, value } }) => (
    <View>
      <TextInput
        value={value}
        onChangeText={onChange}
        onBlur={onBlur}
        style={[styles.input, errors.email && styles.inputError]}
      />
      {errors.email && (
        <Text style={styles.errorText}>{errors.email.message}</Text>
      )}
    </View>
  )}
/>

Handling Form Submission with handleSubmit

Wrap your submit handler with handleSubmit. react-hook-form will run all validation rules first; if any field is invalid, it populates formState.errors and does not call your handler. If all fields are valid, your handler receives a typed object containing all field values — ready to send to an API.

async function onSubmit(data: LoginForm) {
  console.log('Submitting:', data.email, data.password);
  try {
    await authApi.login(data.email, data.password);
    navigation.replace('Home');
  } catch (err) {
    Alert.alert('Login Failed', 'Invalid email or password.');
  }
}

<Button title='Log In' onPress={handleSubmit(onSubmit)} />

Password Field Configuration

For password fields, set secureTextEntry to hide the typed characters and configure an appropriate keyboard type. Wire the field to Controller exactly like the email field. Many apps also add a 'show/hide' icon button that toggles secureTextEntry via local state — this improves accessibility for users with typos.

<Controller
  control={control}
  name='password'
  rules={{
    required: 'Password is required',
    minLength: { value: 8, message: 'Password must be at least 8 characters' },
  }}
  render={({ field: { onChange, onBlur, value } }) => (
    <TextInput
      value={value}
      onChangeText={onChange}
      onBlur={onBlur}
      secureTextEntry
      placeholder='Password'
    />
  )}
/>

Using watch to Observe Field Values

The watch function returned by useForm lets you subscribe to a field's current value and react to changes in real time. A common use case is a 'confirm password' field that validates its value matches the password field. Pass a field name to watch and use the returned value in the confirm field's validate rule.

const { control, handleSubmit, watch, formState: { errors } } = useForm<RegisterForm>();
const password = watch('password');

<Controller
  control={control}
  name='confirmPassword'
  rules={{
    validate: (value) =>
      value === password || 'Passwords do not match',
  }}
  render={({ field }) => <TextInput {...field} secureTextEntry />}
/>

Resetting the Form

Call reset() to clear all field values and errors, returning the form to its default values. You can also pass a new set of values to reset({ email: 'prefilled@example.com' }) to re-initialize the form with different defaults, which is useful for edit-profile forms that pre-populate with existing user data.

// Clear after successful submit:
async function onSubmit(data: LoginForm) {
  await api.login(data);
  reset(); // clears all inputs
}

// Pre-fill with existing profile data:
useEffect(() => {
  if (userProfile) {
    reset({
      name: userProfile.name,
      email: userProfile.email,
    });
  }
}, [userProfile]);

Form Validation Modes

react-hook-form offers several mode settings that control when validation runs: 'onSubmit' (default, validates only on submit), 'onBlur' (validates when a field loses focus), 'onChange' (validates on every keystroke), and 'all' (combines onBlur and onChange). For mobile forms, 'onBlur' offers the best balance between immediate feedback and avoiding distracting errors while typing.

const { control, handleSubmit } = useForm<LoginForm>({
  mode: 'onBlur',       // validate when user leaves a field
  defaultValues: { email: '', password: '' },
});

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: useForm creates the form instance with control, handleSubmit, and formState.errors, Controller wires native TextInput components to the form with onChange, onBlur, and value props, and rules define built-in validation constraints that populate errors automatically. Next up we explore validation rules and error message handling in depth.

Häufig gestellte Fragen

Ist die Lektion „react-hook-form mit Controller einrichten“ kostenlos?

Ja — der vollständige Text von „react-hook-form mit Controller einrichten“ ist hier im Web kostenlos zu lesen. Um sie interaktiv zu üben (integrierter Code-Editor und 24/7 KI-Tutor) und den Rest des React Native Academy-Kurses freizuschalten, upgrade auf CoddyKit PRO. Der React Native Academy-Kurs umfasst insgesamt 4 Lektionen.

Was lerne ich in „react-hook-form mit Controller einrichten“?

Installieren Sie react-hook-form, verwenden Sie useForm, um eine Formularinstanz zu erstellen, und umschließen Sie jedes TextInput mit einem Controller, um es zu registrieren sowie onChange/onBlur zu… Du übst React Native Academy mit praktischem Code, den du direkt im Browser ausführst, und ein 24/7 KI-Tutor beantwortet deine Fragen während du die Lektion bearbeitest.

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react-hook-form mit Controller einrichten
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