TextField and TextEditingController in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you type in this TextField?

Consider this Flutter widget code snippet. What will be the value of the TextEditingController's text after typing "hello" in the TextField?

Flutter

final controller = TextEditingController();

TextField(
  controller: controller,
  decoration: InputDecoration(labelText: 'Enter text'),
);

A The controller.text will remain empty even after typing.

B The controller.text will be "hello" after typing.

C The controller.text will contain "Enter text".

D The controller.text will be null.

💡 Hint

The controller keeps the current text inside the TextField.

The TextEditingController is linked to the TextField. When you type, the controller updates its text property to match the input.

❓ lifecycle

intermediate

When should you dispose a TextEditingController?

In a StatefulWidget, when is the correct time to call dispose() on a TextEditingController?

A After every build() call.

B In the widget's initState() method.

C In the widget's dispose() method.

D You never need to dispose it.

💡 Hint

Think about cleaning up resources when the widget is removed.

TextEditingController holds resources and listeners. To avoid memory leaks, dispose it in the widget's dispose() method.

📝 Syntax

advanced

What is the output of this code snippet?

What will be printed when this Flutter code runs and the TextField is empty, then the button is pressed?

Flutter

final controller = TextEditingController();

ElevatedButton(
  onPressed: () {
    print(controller.text.isEmpty ? 'Empty' : controller.text);
  },
  child: Text('Check'),
);

A Empty

B Prints a blank line

C Throws a runtime error

D null

💡 Hint

Check what controller.text returns when no input is given.

controller.text returns an empty string "" if no text is entered, so isEmpty is true and 'Empty' is printed.

🔧 Debug

advanced

Why does this TextField not update the controller text?

Given this code, why does typing in the TextField not change the controller's text?

Flutter

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

TextField(
  onChanged: (value) {
    controller.text = value;
  },
  controller: controller,
);

A Because setting controller.text inside onChanged causes an infinite loop and blocks updates.

B Because controller.text is read-only and cannot be set.

C Because onChanged is never called when controller is set.

D Because the controller must be recreated on every build.

💡 Hint

Think about what happens when you set controller.text inside onChanged.

Setting controller.text inside onChanged triggers another change event, causing a loop that prevents normal updates.

🧠 Conceptual

expert

How to programmatically move cursor to end of text in TextField?

You want to set the cursor position at the end of the current text in a TextField controlled by a TextEditingController. Which code snippet achieves this?

A controller.setCursor(offset: controller.text.length);

B controller.moveCursorToEnd();

C controller.cursorPosition = controller.text.length;

D controller.selection = TextSelection.fromPosition(TextPosition(offset: controller.text.length));

💡 Hint

Look for how to set selection using TextSelection and TextPosition.

To move the cursor, set controller.selection to a TextSelection at the desired offset. The other options are invalid methods or properties.

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