Ten Ways to Avoid Mistakes

IN THIS CHAPTER

check Spotting common errors

check Using proper code style

Put Capital Letters Where They Belong

The Dart language is case-sensitive. Don’t type Class when you mean to type class. Don’t type Runapp when you mean to type runApp.

Use Parentheses When (and Only When) They’re Appropriate

Remember the difference between _incrementCounter with parentheses:

void _incrementCounter() { setState(() { _counter++; }); }

and _incrementCounter without parentheses:

floatingActionButton: FloatingActionButton( onPressed: _incrementCounter, tooltip: 'Increment', child: Icon(Icons.add), )

For details, refer to Chapter 5.

Limit Access to Variables

Wherever you can, avoid declaring top-level variables. To keep other files from changing your file’s variables, start variable names with an underscore. (Refer to Chapter 5.)

Call setState

If you press a widget and nothing happens, look for a method with a missing setState call. (Refer to Chapter 5.)

Make Adjustments for Indices Starting at Zero

To make values start with 1, you have to add 1 (Refer to Chapter 8.):

return ListView.builder( itemCount: 25, itemBuilder: (context, index) => ListTile( title: Text('Rocky ${index + 1}'), onTap: () => goToDetailPage(index + 1), ), );

Use the Expanded Widget

When your test device displays black-and-yellow stripes or an empty screen, the layout you’ve coded is causing trouble. Consider wrapping one or more widgets inside Expanded widgets. Sometimes, it works wonders. (Refer to Chapters 6 and 8.)

Add itemCount to Your ListView.builder

Without an itemCount parameter, the list of items never ends. (Refer to Chapter 8.)

Add Imports When They’re Required

For example, if you want to use Dart’s math library, start your file with

import 'dart:math';

If your app pulls data from the Internet, add this line to the top of your file:

import 'package:http/http.dart';

For details, refer to Chapters 8 and 9.

Declare Assets and Dependencies in pubspec.yaml

To display brokenheart.jpg and heart.jpg on the screen, add some lines to your project’s pubspec.yaml file:

assets: - brokenheart.jpeg - heart.jpeg

To get data from the Internet, add http to the file’s list of dependencies:

dependencies: flutter: sdk: flutter http: ^0.12.0+4

For details, refer to Chapters 3 and 8. And remember, in a pubspec.yaml file, indentation matters.

Indent Your Code According to Dart Language Guidelines

Code that’s not properly indented is difficult to read and difficult to maintain. Format your code by selecting Code ⇒ Reformat Code from Android Studio’s main menu.