Hello, fellow Flutter/Dart enthusiasts! If you're looking to give your apps a performance boost, then you're in for a treat! Today, we're going to explore the magic of deferred imports in Dart. By the end of this post, you'll learn how to lazy-load libraries, which can significantly improve the initial startup time of your apps.

So buckle up and let's dive right in!

The Power of Deferred Imports

Imagine you're working on a fantastic Dart application that requires a heavy library (like an image processing library). Now, loading this library can slow down your app's startup time, and we don't want that, right? That's where deferred imports come to our rescue!

In Dart, the deferred keyword allows you to lazy-load a library, meaning it's only loaded when it's actually needed. Combine this with the as keyword to create an alias for the imported library, and you're all set! Here's an example:

import 'package:heavy_library/heavy_library.dart' deferred as heavyLibrary;

A Step-by-Step Guide to Deferred Imports

Once you've declared the import using the deferred keyword, you'll need to load the library explicitly before using its members. You do this by calling the loadLibrary() function on the alias. Let's walk through a complete example:

1. First, let's import our required libraries. We'll import dart:async for working with Future, and our heavy library using the deferred keyword:

import 'dart:async';
import 'package:heavy_library/heavy_library.dart' deferred as heavyLibrary;

1. Now, create a main function that will act as the entry point for our application:

Future<void> main() async {
  print('Application started.');

  // Perform some operations before loading the heavy library.
  await Future.delayed(Duration(seconds: 2));

  // Load the heavy library.
  await heavyLibrary.loadLibrary();
  print('Heavy library loaded.');

  // Use the heavy library.
  heavyLibrary.heavyFunction();
  print('Heavy function executed.');
}

In this example, the heavy_library package is imported using the deferred keyword and aliased as heavyLibrary. The main function of the application performs some operations before loading the heavy library using await heavyLibrary.loadLibrary(). Once the library is loaded, you can call its members, like heavyLibrary.heavyFunction() in this example.

And that's it! You've just mastered the art of deferred imports in Dart!

Wrapping Up

Now that you know how to use deferred imports in Dart, you can boost the performance of your apps by only loading heavy libraries when they're truly needed. This can be a game-changer, especially for large applications with numerous dependencies.

So go on, give your Dart apps a performance boost, and keep coding! 🚀

Credit for this post: Reham Ali's LinkedIn Post 🤌