Text themes in Flutter - Mini App: Build & Ship

Build: Text Theme Demo

This screen shows different text styles using Flutter's text themes. It helps users see how to apply and customize text styles globally.

Target UI

-------------------------
| Text Theme Demo       |
|-----------------------|
| Title Text            |
| Subtitle Text         |
| Body Text             |
| Caption Text          |
| Button Text           |
|-----------------------|

Use Theme.of(context).textTheme to style all text widgets

Display five Text widgets with styles: headline6, subtitle1, bodyText2, caption, button

Use a Scaffold with AppBar titled 'Text Theme Demo'

Center the text widgets vertically with some spacing

Starter Code

Flutter

import 'package:flutter/material.dart';

class TextThemeDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Text Theme Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            // TODO: Add Text widgets with different textTheme styles here
          ],
        ),
      ),
    );
  }
}

Task 1

Task 2

Task 3

Task 4

Task 5

Task 6

Task 7

Solution

Flutter

import 'package:flutter/material.dart';

class TextThemeDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final textTheme = Theme.of(context).textTheme;
    return Scaffold(
      appBar: AppBar(
        title: Text('Text Theme Demo'),
      ),
      body: Center(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: [
            Text('Title Text', style: textTheme.headline6),
            SizedBox(height: 8),
            Text('Subtitle Text', style: textTheme.subtitle1),
            SizedBox(height: 8),
            Text('Body Text', style: textTheme.bodyText2),
            SizedBox(height: 8),
            Text('Caption Text', style: textTheme.caption),
            SizedBox(height: 8),
            Text('Button Text', style: textTheme.button),
          ],
        ),
      ),
    );
  }
}

This code uses Flutter's built-in Theme.of(context).textTheme to style text consistently across the app. Each Text widget uses a different style from the text theme: headline6 for the title, subtitle1 for subtitle, bodyText2 for body text, caption for small caption text, and button style for button text style. The SizedBox widgets add vertical spacing between the texts for better readability. This approach helps maintain a consistent look and feel and makes it easy to update text styles app-wide.

Final Result

Completed Screen

-------------------------
| Text Theme Demo       |
|-----------------------|
| Title Text            |
|                       |
| Subtitle Text         |
|                       |
| Body Text             |
|                       |
| Caption Text          |
|                       |
| Button Text           |
|-----------------------|

Screen shows five lines of text with different styles from the app's text theme

No interactive elements on this screen

Stretch Goal

Add a toggle button in the AppBar to switch between light and dark text themes

💡 Hint

Use a StatefulWidget and ThemeMode to switch themes; update textTheme accordingly

Practice

1. What is the main purpose of using TextTheme in a Flutter app?

easy

A. To keep text styles consistent across the entire app

B. To create animations for text widgets

C. To load external fonts dynamically

D. To handle user input in text fields

Solution

1. Step 1: Understand the role of TextTheme

   TextTheme defines a set of text styles used throughout the app to maintain consistency.

2. Step 2: Compare with other options

   Options A, C, and D relate to animations, fonts, and input handling, which are not the purpose of TextTheme.

3. Final Answer:

   To keep text styles consistent across the entire app -> Option A

4. Quick Check:

   TextTheme = consistent text styles [OK]

Hint: TextTheme is for consistent text styles app-wide [OK]

Common Mistakes:

• Confusing TextTheme with animation or input handling
• Thinking TextTheme loads fonts
• Assuming TextTheme is for user interaction

2. Which of the following is the correct way to access the headline1 text style from the current theme inside a widget's build method?

easy

A. TextTheme.headline1(context)

B. Theme.textTheme.headline1

C. context.textTheme.headline1

D. Theme.of(context).textTheme.headline1

Solution

1. Step 1: Recall the correct syntax to access text styles

   Use Theme.of(context).textTheme.styleName to get a text style from the current theme.

2. Step 2: Check each option

   Theme.of(context).textTheme.headline1 matches the correct syntax. Options A, B, and D use incorrect or invalid syntax.

3. Final Answer:

   Theme.of(context).textTheme.headline1 -> Option D

4. Quick Check:

   Access text style = Theme.of(context).textTheme.style [OK]

Hint: Use Theme.of(context).textTheme.styleName to get styles [OK]

Common Mistakes:

• Omitting Theme.of(context)
• Trying to call textTheme as a method
• Using context.textTheme directly

3. What will be the color of the text rendered by this code snippet?

Text(
  'Hello',
  style: Theme.of(context).textTheme.bodyText1?.copyWith(color: Colors.red),
)

Assuming the app's theme sets bodyText1 color to blue.

medium

A. Red

B. Blue

C. Default black

D. Transparent

Solution

1. Step 1: Understand style overriding with copyWith

   The copyWith method creates a copy of the original style but overrides specified properties, here the color is set to red.

2. Step 2: Determine final color

   Even though bodyText1 color is blue in the theme, the copyWith(color: Colors.red) changes it to red.

3. Final Answer:

   Red -> Option A

4. Quick Check:

   copyWith overrides color to red [OK]

Hint: copyWith overrides original style properties [OK]

Common Mistakes:

• Assuming original theme color remains unchanged
• Ignoring copyWith effect
• Thinking default black applies

4. Identify the error in this Flutter code snippet that tries to apply a text theme style:

Text(
  'Welcome',
  style: Theme.textTheme.headline6,
)

medium

A. Text widget cannot use style property

B. headline6 is not a valid text style

C. Missing context in Theme.of(context) call

D. Text string must be wrapped in a TextSpan

Solution

1. Step 1: Check how Theme is accessed

   The code uses Theme.textTheme.headline6 which is invalid because Theme is a class and requires context to access the current theme.

2. Step 2: Correct usage

   The correct way is Theme.of(context).textTheme.headline6 to get the style from the current context.

3. Final Answer:

   Missing context in Theme.of(context) call -> Option C

4. Quick Check:

   Theme.of(context) needed to access theme [OK]

Hint: Always use Theme.of(context) to get theme data [OK]

Common Mistakes:

• Using Theme without context
• Assuming headline6 is invalid
• Thinking Text needs TextSpan for style

5. You want to create a custom text theme where the subtitle1 style uses a font size of 18 and green color. Which code snippet correctly defines this inside ThemeData.textTheme?

hard

A. textTheme: TextTheme(subtitle1: TextStyle(font: 18, color: Colors.green))

B. textTheme: TextTheme(subtitle1: TextStyle(fontSize: 18, color: Colors.green))

C. textTheme: TextTheme(subtitle1: TextStyle(fontSize: 18, color: 'green'))

D. textTheme: TextTheme(subtitle1: TextStyle(size: 18, color: Colors.green))

Solution

1. Step 1: Identify correct TextStyle properties

   The correct property for font size is fontSize and color must be a Color object like Colors.green.

2. Step 2: Evaluate each option

   textTheme: TextTheme(subtitle1: TextStyle(fontSize: 18, color: Colors.green)) uses correct property names and values. textTheme: TextTheme(subtitle1: TextStyle(size: 18, color: Colors.green)) uses size which is invalid. textTheme: TextTheme(subtitle1: TextStyle(fontSize: 18, color: 'green')) uses a string for color instead of a Color object. textTheme: TextTheme(subtitle1: TextStyle(font: 18, color: Colors.green)) uses font which is invalid.

3. Final Answer:

   textTheme: TextTheme(subtitle1: TextStyle(fontSize: 18, color: Colors.green)) -> Option B

4. Quick Check:

   fontSize and Colors.green are correct [OK]

Hint: Use fontSize and Colors.green for size and color [OK]

Common Mistakes:

• Using 'size' instead of fontSize
• Passing color as string instead of Color object
• Using invalid property names like font