TextField and TextEditingController in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a TextField that uses a controller.

Flutter

final myController = TextEditingController();

TextField(controller: [1]);

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

AmyController

BTextEditingController()

Ccontroller

DTextField()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a new TextEditingController() directly inside the TextField instead of the variable.

Using the wrong property name instead of controller.

The controller property of TextField needs the variable myController that holds the TextEditingController instance.

2fill in blank

medium

Complete the code to clear the text inside the TextEditingController.

Flutter

myController.[1]();

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

Aclear

Bremove

Creset

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using methods like reset() or delete() which do not exist on TextEditingController.

Trying to assign an empty string directly to the controller.

The clear() method empties the text inside the TextEditingController.

3fill in blank

hard

Fix the error in the code to properly dispose the TextEditingController in a StatefulWidget.

Flutter

@override
void dispose() {
  [1].dispose();
  super.dispose();
}

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

ATextEditingController

BmyController

Cdispose

Dcontroller

Attempts:

3 left

💡 Hint

Common Mistakes

Calling dispose() on the class name instead of the instance.

Forgetting to call super.dispose() after disposing the controller.

You must call dispose() on the controller variable (here myController) to free resources when the widget is removed.

4fill in blank

hard

Fill both blanks to create a TextField that updates a variable when text changes.

Flutter

String text = '';

TextField(
  onChanged: ([1]) {
    [2] = value;
  },
);

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

Avalue

Btext

Ccontroller

Dinput

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong parameter name that does not match the callback signature.

Assigning to a wrong variable name.

The onChanged callback receives the new text as value. We assign it to the variable text to keep track of the input.

5fill in blank

hard

Fill all three blanks to create a TextEditingController, assign it to a TextField, and dispose it properly.

Flutter

class MyWidget extends StatefulWidget {
  @override
  State<MyWidget> createState() => _MyWidgetState();
}

class _MyWidgetState extends State<MyWidget> {
  final [1] = TextEditingController();

  @override
  void dispose() {
    [2].dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return TextField(controller: [3]);
  }
}

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

AmyController

Dcontroller

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in different places causing errors.

Forgetting to dispose the controller.

The same variable myController is created, disposed, and assigned to the TextField controller.

Practice

1. What is the main purpose of a TextEditingController in Flutter when used with a TextField?

easy

A. To read, set, and listen to the text input in the TextField

B. To style the TextField with colors and fonts

C. To handle button clicks inside the TextField

D. To navigate between different screens

Solution

1. Step 1: Understand TextEditingController role

   TextEditingController connects your code to the TextField's text, allowing you to read or change it.

2. Step 2: Compare with other options

   Styling, button clicks, and navigation are unrelated to TextEditingController's main function.

3. Final Answer:

   To read, set, and listen to the text input in the TextField -> Option A

4. Quick Check:

   TextEditingController manages text content [OK]

Hint: Remember: Controller manages text, not style or navigation [OK]

Common Mistakes:

• Confusing controller with styling properties
• Thinking controller handles button clicks
• Assuming controller manages navigation

2. Which of the following is the correct way to create a TextEditingController and assign it to a TextField in Flutter?

easy

A. final controller = TextFieldController();
TextField(controller: controller);

B. final controller = TextEditingController();
TextField(controller: controller);

C. final controller = TextEditingController();
TextField(textController: controller);

D. final controller = TextEditingController();
TextField(control: controller);

Solution

1. Step 1: Check correct class name and usage

   The correct class is TextEditingController and the TextField property is controller.

2. Step 2: Verify options

   final controller = TextEditingController(); TextField(controller: controller); uses correct class and property names. Options A, C, and D have wrong class or property names.

3. Final Answer:

   final controller = TextEditingController();\nTextField(controller: controller); -> Option B

4. Quick Check:

   Use TextEditingController and controller property [OK]

Hint: Remember exact names: TextEditingController and controller [OK]

Common Mistakes:

• Using wrong class name like TextFieldController
• Using wrong property names like textController or control
• Forgetting to assign controller to TextField

3. Consider this Flutter code snippet:

final controller = TextEditingController(text: 'Hello');

TextField(controller: controller);

print(controller.text);

What will be printed in the console?

medium

A. Hello

B. null

C. Empty string

D. Error: controller.text not set

Solution

1. Step 1: Check initial text in controller

   The controller is created with initial text 'Hello'.

2. Step 2: Understand controller.text value

   controller.text returns the current text, which is 'Hello' initially.

3. Final Answer:

   Hello -> Option A

4. Quick Check:

   Initial text in controller.text is 'Hello' [OK]

Hint: Initial text in controller.text is what prints [OK]

Common Mistakes:

• Assuming controller.text is null if not typed
• Thinking print shows empty string by default
• Expecting error without user input

4. What is wrong with this Flutter code snippet?

final controller = TextEditingController();

TextField(controller: controller);

controller.dispose();

Choose the best explanation.

medium

A. TextField requires controller to be final, so this code is invalid

B. TextEditingController cannot be assigned to TextField controller property

C. Calling dispose() immediately after creating controller causes errors when TextField uses it

D. dispose() should be called before creating the controller

Solution

1. Step 1: Understand dispose() usage

   dispose() frees resources and should be called when controller is no longer needed, not immediately after creation.

2. Step 2: Analyze code behavior

   Calling dispose() right after creation means TextField tries to use a disposed controller, causing errors.

3. Final Answer:

   Calling dispose() immediately after creating controller causes errors when TextField uses it -> Option C

4. Quick Check:

   Dispose only after widget lifecycle ends [OK]

Hint: Dispose controllers only when widget is disposed [OK]

Common Mistakes:

• Calling dispose() too early
• Confusing dispose() timing
• Thinking dispose() is needed before creation

5. You want to clear the text inside a TextField when a button is pressed. Which code snippet correctly achieves this using TextEditingController?

hard

A. final controller = TextEditingController();

ElevatedButton(onPressed: () {
controller.dispose();
}, child: Text('Clear'));

TextField(controller: controller);

B. final controller = TextEditingController();

ElevatedButton(onPressed: () {
controller.text = null;
}, child: Text('Clear'));

TextField(controller: controller);

C. final controller = TextEditingController();

ElevatedButton(onPressed: () {
controller.reset();
}, child: Text('Clear'));

TextField(controller: controller);

D. final controller = TextEditingController();

ElevatedButton(onPressed: () {
controller.clear();
}, child: Text('Clear'));

TextField(controller: controller);

Solution

1. Step 1: Identify method to clear text

   TextEditingController has a clear() method to empty the text.

2. Step 2: Check other options for correctness

   Setting text to null causes error, dispose() frees resources (not clearing), reset() does not exist.

3. Final Answer:

   Use controller.clear() inside button onPressed to clear text -> Option D

4. Quick Check:

   Use clear() to empty TextField text [OK]

Hint: Use controller.clear() to empty text field quickly [OK]

Common Mistakes:

• Setting controller.text to null (causes error)
• Calling dispose() instead of clear()
• Using non-existent reset() method