Why form handling captures user data in React Native - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to capture user input in a React Native TextInput.

React Native

const [name, setName] = useState('');

<TextInput value={name} onChangeText=[1] placeholder="Enter name" />

Drag options to blanks, or click blank then click option'

AhandleChange

Bname

CsetName

DgetName

Attempts:

3 left

💡 Hint

Common Mistakes

Using the state variable instead of the setter function.

Passing a function name that is not defined.

The onChangeText prop expects a function to update the state. setName updates the name state with user input.

2fill in blank

medium

Complete the code to handle form submission and log the captured data.

React Native

const handleSubmit = () => {
  console.log('User name:', [1]);
};

Drag options to blanks, or click blank then click option'

Aname

BsetName

ChandleSubmit

DuserName

Attempts:

3 left

💡 Hint

Common Mistakes

Using the setter function instead of the state variable.

Using an undefined variable.

The name variable holds the current user input captured from the form.

3fill in blank

hard

Fix the error in the code to correctly update multiple form fields in state.

React Native

const [form, setForm] = useState({ email: '', password: '' });

const handleEmailChange = (text) => {
  setForm({ ...form, [1]: text });
};

Drag options to blanks, or click blank then click option'

Apassword

Bemail

Ctext

Dform

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong key like 'password' when updating email.

Using a variable name instead of a key string.

To update the email field in the form state, use the key email in the object spread.

4fill in blank

hard

Fill both blanks to create a controlled TextInput for password with secure entry.

React Native

<TextInput value={form.[1] onChangeText={(text) => setForm({ ...form, [2]: text })} secureTextEntry={true} placeholder="Password" />

Drag options to blanks, or click blank then click option'

Apassword

Bemail

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up 'email' and 'password' keys.

Not matching the value and update keys.

The value and the key in setForm must both be password to keep the input controlled and update the correct field.

5fill in blank

hard

Fill all three blanks to create a form submission handler that prevents default, logs data, and resets form.

React Native

const handleSubmit = (event) => {
  event.[1]();
  console.log('Form data:', [2]);
  setForm({ [3] });
};

Drag options to blanks, or click blank then click option'

ApreventDefault

Bform

Cemail: '', password: ''

DstopPropagation

Attempts:

3 left

💡 Hint

Common Mistakes

Using stopPropagation instead of preventDefault.

Logging the setter function instead of form data.

Not resetting form fields properly.

Calling preventDefault() stops the page reload. Logging form shows the data. Resetting form clears the fields.

Practice

1. Why do we use state variables when handling forms in React Native?

easy

A. To store and update the user input dynamically

B. To style the form components

C. To navigate between screens

D. To fetch data from the internet

Solution

1. Step 1: Understand the role of state in forms

   State variables hold the current value typed by the user in the form fields.

2. Step 2: Recognize dynamic updates

   State updates as the user types, so the app always has the latest input data.

3. Final Answer:

   To store and update the user input dynamically -> Option A

4. Quick Check:

   State holds user input live for forms [OK]

Hint: State holds user input live for forms [OK]

Common Mistakes:

• Thinking state is for styling
• Confusing state with navigation
• Assuming state fetches data automatically

2. Which of the following is the correct way to update a state variable named name when user types in a TextInput?

easy

A. onInput={(text) => setName(text)}

B. onChange={(text) => setName(text)}

C. onTextChange={(text) => setName(text)}

D. onChangeText={(text) => setName(text)}

Solution

1. Step 1: Identify the correct event prop for TextInput

   React Native uses onChangeText to capture text changes.

2. Step 2: Match the syntax to update state

   The function setName is called with the new text value.

3. Final Answer:

   onChangeText={(text) => setName(text)} -> Option D

4. Quick Check:

   Use onChangeText to update input state [OK]

Hint: Use onChangeText to update input state [OK]

Common Mistakes:

• Using onChange instead of onChangeText
• Using wrong event names like onTextChange
• Not passing the text parameter correctly

3. What will be displayed on screen after typing 'Hello' in this React Native form snippet?

const [text, setText] = useState('');
return (
  <>
    
    You typed: {text}
  </>
);

medium

A. You typed: Hello

B. You typed:

C. You typed: undefined

D. You typed: null

Solution

1. Step 1: Understand state update on typing

   Typing 'Hello' triggers setText to update text to 'Hello'.

2. Step 2: Check displayed text

   The Text component shows 'You typed: ' plus the current text value.

3. Final Answer:

   You typed: Hello -> Option A

4. Quick Check:

   Text shows current state value typed by user [OK]

Hint: Text shows current state value typed by user [OK]

Common Mistakes:

• Expecting empty or undefined text after typing
• Not linking TextInput value to state
• Forgetting to update state on text change

4. Identify the error in this React Native form code:

const [email, setEmail] = useState('');
return (
  
);

medium

A. useState must be called inside the TextInput

B. value should not be set for controlled inputs

C. onChangeText should be a function, not a state variable

D. setEmail should be passed as value

Solution

1. Step 1: Check onChangeText prop usage

   It must be a function to update state, but here it is the state variable email.

2. Step 2: Understand correct usage

   We should pass setEmail to onChangeText to update the state.

3. Final Answer:

   onChangeText should be a function, not a state variable -> Option C

4. Quick Check:

   onChangeText must be a function to update state [OK]

Hint: onChangeText must be a function to update state [OK]

Common Mistakes:

• Passing state variable instead of setter function
• Removing value prop for controlled input
• Misplacing useState call

5. You want to capture user input from two fields, username and password, and show a message only when both are filled. Which approach correctly handles this in React Native?

const [form, setForm] = useState({username: '', password: ''});

// What should onChangeText for username be?
// And how to check if both fields are filled?

hard

A. Use separate states for each field and check username || password

B. Use onChangeText={text => setForm({...form, username: text})} and check form.username && form.password

C. Use onChangeText={setForm} and check form.username === ''

D. Use onChangeText={text => setForm(text)} and check form.length > 0

Solution

1. Step 1: Update nested state correctly

   Use spread operator to keep other fields and update only username: setForm({...form, username: text}).

2. Step 2: Check both fields are filled

   Check if both form.username and form.password are truthy (not empty strings).

3. Final Answer:

   Use onChangeText={text => setForm({...form, username: text})} and check form.username && form.password -> Option B

4. Quick Check:

   Use spread to update form object and check both fields [OK]

Hint: Use spread to update form object and check both fields [OK]

Common Mistakes:

• Overwriting whole form state instead of merging
• Using OR instead of AND to check fields
• Passing wrong function to onChangeText