フォームの送信とリセット
handleSubmitでフォーム送信を処理し、検証済みの値でAPIを呼び出します。成功メッセージまたはサーバー側のエラーメッセージを表示し、成功時にフォームをリセットします。
「フォームの送信とリセット」はCoddyKit上の無料React Native Academyレッスンです。 これはレッスン4/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはReact Native Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 React Native Academyコースには全4レッスンが含まれています。
このレッスンの一部はまだ翻訳されておらず、英語で表示されています。
The handleSubmit Wrapper
handleSubmit from useForm is a higher-order function that wraps your submit handler. When called, it first runs all validation rules. If every field passes, it calls your handler with the typed form data. If any field fails, it populates formState.errors and does not call your handler. Never read form values directly from state inside the submit handler — always use the typed data argument that handleSubmit provides.
const { handleSubmit } = useForm<LoginForm>();
async function onSubmit(data: LoginForm) {
// data is fully typed — guaranteed to have passed validation
console.log(data.email, data.password);
await authApi.login(data.email, data.password);
}
// Wire to button:
<Button title='Log In' onPress={handleSubmit(onSubmit)} />Making an API Call in the Submit Handler
The submit handler is an async function — handleSubmit handles the Promise automatically. Make your API call inside a try-catch block. On success, navigate to the next screen or show a success message. On failure, use setError to show a field-level error or display a general error with Alert.
async function onSubmit(data: RegisterForm) {
try {
await api.register({
email: data.email,
password: data.password,
name: data.name,
});
navigation.replace('Home');
} catch (err: any) {
if (err.status === 409) {
setError('email', { message: 'This email is already in use.' });
} else {
Alert.alert('Registration Failed', 'Please try again later.');
}
}
}isSubmitting to Block Double Submissions
formState.isSubmitting is automatically set to true while your async submit handler is running and to false when it completes. Use it to disable the submit button during the API call. Without this guard, fast double-taps can submit the form twice, causing duplicate records on the server or charging a user twice.
const { handleSubmit, formState: { isSubmitting } } = useForm<LoginForm>();
return (
<View>
{/* ... form fields ... */}
<TouchableOpacity
onPress={handleSubmit(onSubmit)}
disabled={isSubmitting}
style={[styles.button, isSubmitting && styles.buttonDisabled]}
>
{isSubmitting
? <ActivityIndicator color='white' />
: <Text style={styles.buttonText}>Log In</Text>
}
</TouchableOpacity>
</View>
);Handling Submission Errors from the Server
When the server returns a general error (not tied to a specific field), display it near the submit button or in an error banner above the form. Use a local serverError state variable that you set in the catch block. This separates server-level errors from field-level validation errors and gives users a clear message about what went wrong.
const [serverError, setServerError] = React.useState<string | null>(null);
async function onSubmit(data: LoginForm) {
setServerError(null); // clear previous error
try {
await api.login(data);
navigation.replace('Dashboard');
} catch {
setServerError('Login failed. Please check your credentials.');
}
}
// In render:
{serverError && (
<Text style={styles.serverError}>{serverError}</Text>
)}Showing a Success State
After a successful submission, provide clear feedback before navigating away. An inline success message, a check-mark animation, or a brief delay before navigation all help users feel confident the action completed. For forms like contact or feedback submission that do not navigate away, reset the form and show a success banner in place of the submit button.
const [submitted, setSubmitted] = React.useState(false);
async function onSubmit(data: FeedbackForm) {
await api.sendFeedback(data);
setSubmitted(true);
reset();
}
if (submitted) {
return (
<View style={styles.success}>
<Ionicons name='checkmark-circle' size={64} color='green' />
<Text>Thank you! Your feedback was sent.</Text>
</View>
);
}Resetting to Default Values
Call reset() with no arguments to clear all fields back to their defaultValues and also clear all errors. This is useful for 'Send Another' flows where the user wants to submit the same form type multiple times, or for forms that appear in a modal and need to be blank when reopened. The reset is synchronous and immediate.
const { reset } = useForm<ContactForm>({
defaultValues: { name: '', email: '', message: '' },
});
async function onSubmit(data: ContactForm) {
await api.sendMessage(data);
reset(); // all fields cleared, errors cleared
Alert.alert('Sent!', 'Your message has been delivered.');
}Resetting to New Values
Pass a value object to reset(newValues) to replace the default values and repopulate the form at the same time. This is the correct way to pre-fill an edit form with data loaded from the server. Call reset inside a useEffect that runs when the server data arrives to populate all fields without triggering field-level validation.
const { reset } = useForm<ProfileForm>();
useEffect(() => {
if (userProfile) {
reset({
name: userProfile.name,
bio: userProfile.bio,
website: userProfile.website ?? '',
});
}
}, [userProfile, reset]);Resetting Individual Fields with setValue
Sometimes you only want to reset or update one specific field without clearing the entire form. Use setValue(fieldName, newValue) for targeted updates. An optional third argument { shouldValidate: true } re-runs validation for that field after the value is set, useful when you programmatically change a field and want errors to update immediately.
const { setValue } = useForm<AddressForm>();
async function handleLocationPress() {
const loc = await Location.getCurrentPositionAsync({});
const [address] = await Location.reverseGeocodeAsync(loc.coords);
setValue('city', address.city ?? '', { shouldValidate: true });
setValue('postalCode', address.postalCode ?? '');
}isDirty and Unsaved Changes Guard
formState.isDirty is true when any field value differs from its default value. Use this to warn the user before they navigate away from an unsaved form. Hook into navigation's beforeRemove event (React Navigation) to show a 'Discard changes?' alert when the form is dirty and the user tries to go back.
const { formState: { isDirty } } = form;
useEffect(() => {
const unsubscribe = navigation.addListener('beforeRemove', (e) => {
if (!isDirty) return;
e.preventDefault();
Alert.alert('Discard changes?', 'You have unsaved changes.', [
{ text: 'Keep Editing', style: 'cancel' },
{ text: 'Discard', style: 'destructive',
onPress: () => navigation.dispatch(e.data.action) },
]);
});
return unsubscribe;
}, [navigation, isDirty]);Validating on Demand with trigger
You can call trigger() with no arguments to validate all fields at any time — not just on submit. Call it when the user taps a 'Check' button, when they reach the end of a scrollable form, or to pre-validate before switching tabs. This is useful for showing all errors at once so users can fix everything before hitting the submit button.
const { trigger, formState: { errors } } = useForm<RegisterForm>();
async function handleCheckAll() {
const isValid = await trigger();
if (!isValid) {
Alert.alert('Please fix the highlighted fields before submitting.');
}
}Complete Login Form Example
Here is a production-ready login form combining everything from this lesson: typed useForm, Controller-wrapped inputs, validation rules, isSubmitting guard, server error display, and navigation on success. This template can be adapted for any authentication or data entry screen in a React Native app.
export default function LoginScreen() {
const { control, handleSubmit, formState: { errors, isSubmitting } } = useForm<LoginForm>();
const [serverError, setServerError] = React.useState<string | null>(null);
async function onSubmit(data: LoginForm) {
setServerError(null);
try {
await authApi.login(data.email, data.password);
navigation.replace('Home');
} catch { setServerError('Invalid credentials.'); }
}
return (
<View style={styles.container}>
{serverError && <Text style={styles.serverError}>{serverError}</Text>}
<EmailController control={control} error={errors.email} />
<PasswordController control={control} error={errors.password} />
<Button title={isSubmitting ? 'Logging in...' : 'Log In'}
onPress={handleSubmit(onSubmit)} disabled={isSubmitting} />
</View>
);
}Quick Check
Test your understanding of React Native Mobile Development concepts from this lesson.
Lesson Recap
In this lesson you learned: handleSubmit validates all fields before calling your async handler and sets isSubmitting automatically, reset() clears the form while reset(newValues) repopulates it for edit scenarios, and isDirty guards against accidental data loss by warning before navigation. Next we begin the B2 courses, starting with Supabase integration in React Native.
よくある質問
「フォームの送信とリセット」レッスンは無料ですか？
はい。「フォームの送信とリセット」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、React Native Academyコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 React Native Academyコースには全4レッスンが含まれています。
「フォームの送信とリセット」で何を学びますか？
handleSubmitでフォーム送信を処理し、検証済みの値でAPIを呼び出します。成功メッセージまたはサーバー側のエラーメッセージを表示し、成功時にフォームをリセットします。 ブラウザで直接実行するハンズオンコードでReact Native Academyを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。
React Native Academyを始めるのに経験は必要ですか？
事前経験は必要ありません。CoddyKitのReact Native Academyは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン4/4です。
「フォームの送信とリセット」レッスンにはどのくらい時間がかかりますか？
ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。
このReact Native Academyレッスンでコードを書いて実行できますか？
はい。すべてのReact Native Academyレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。