31.72 Flutter Style Constants

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How to Name a Constant

Historically I have preferred SCREAMING_CAPS for my constants. This is a traditional approach but is effective in clearly identifying what is a CONSTANT. However, in dart the recommendation is to use lower camel case. Within the code it is not so clear what is a constant and what is a variable, but there is often no specific need to know the difference. This is perhaps okay as the compiler picks up any errant assignments to a constant. For flutter I recommend this style too.

Preferred

const int windowWidth = 1234;

Discouraged

const int WINDOW_WIDTH = 12345;

Then, within my code when using windowWidth it is not clear whether that is a variable or a constant or a instance, etc. But that is probably okay.

Why Define a Constant

A value that is never to change. Also it tells the compiler this fact and the compiler can take advantage of this in optimising the code and in reloading the code.

Example of an implicit variable and a constant:

var monthsInYear = 12;
const daysInYear = 365;

A final variable (which is also a constant) is assigned its value at runtime.

final today = DateTime.now();

Where to Define Constants

Constants that are required in multiple dart files belong within lib/constants/ and perhaps to start with in lib/constants/app.dart. These constants might be the title/name of the app, locations shared across the app, like assets, and could also include layout type constants like padding and spacing. As the app and number of constants grow, then specific collections of constants might move to their own files within lib/constants/. For example, constants used for styling the app might be in lib/constants/colours.dart or lib/constants/fonts.dart. Constants that are used for spacing the widgets throughout the app might go into lib/constants/spacing.dart.

Constants that are specific to a page or widget or some other specific dart file, and not shared across other files, should go into the specific dart source file.

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