Flutter Web: Only loads app update after second reload

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04-10-2024

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Flutter Web: The "Double Reload" Mystery Solved

Have you ever encountered a frustrating situation in your Flutter Web app where changes you made to the code only reflect after you refresh the page twice? This behavior, often referred to as the "double reload" issue, can be a real head-scratcher for developers. Let's delve into the reasons behind this behavior and equip you with solutions to ensure your Flutter Web app updates seamlessly.

The Scenario:

Imagine this:

1. You make a code change in your Flutter app.
2. You save the file.
3. You hit F5 (or refresh the page) in your browser.
4. Nothing happens! The change is not reflected.
5. You refresh the page again.
6. Aha! The change is finally visible.

Why does this happen?

The Code (and the Culprit):

Let's look at a basic example:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('My Flutter App'),
        ),
        body: Center(
          child: Text('Hello World!'),
        ),
      ),
    );
  }
}

The problem lies in how Flutter Web handles hot reload and the way browser caches operate. When you make a change and refresh, Flutter Web doesn't always fully re-render the app immediately. It often relies on the browser cache for certain resources, which can lead to the "double reload" issue.

Unraveling the Mystery:

Here's a breakdown of what's happening:

1. Initial Load: The first time you load your app, all the assets (like images, fonts, and code) are downloaded and cached by your browser.
2. First Reload: You make a code change and refresh. Flutter Web might not recognize the change as significant enough to invalidate the entire cache. It might only re-render the parts of your app that are directly impacted by the change, leaving the cached assets intact.
3. Second Reload: The second refresh often triggers a complete cache invalidation. The browser downloads the updated assets, leading to the change being reflected in your app.

Solving the "Double Reload" Issue:

Here are several effective strategies to overcome this issue:

1. Hard Reload: Instead of a regular refresh (F5), use a hard reload (Ctrl+Shift+R or Cmd+Shift+R). This forces the browser to clear its cache and fetch all resources from the server, guaranteeing the update is reflected.
2. Disable Browser Cache: Configure your browser to disable caching for development purposes. This ensures that your browser always downloads the latest version of your app.
3. Use flutter run -d chrome --web-allow-file-access: Running your app with this command bypasses the browser cache entirely, forcing the app to reload from scratch on every change.
4. Utilize Hot Reload Effectively: While hot reload might not always work flawlessly, it's a powerful tool. Make sure you're correctly using it to avoid unnecessary cache invalidation.
5. Consider Using a Build Tool: Tools like flutter build web generate optimized builds that are less susceptible to caching issues.

Conclusion:

The "double reload" issue in Flutter Web is a common obstacle, but understanding the reasons behind it allows you to address it effectively. By employing the strategies outlined above, you can ensure your Flutter Web app updates smoothly and consistently. Remember to choose the method that best suits your development workflow and enjoy a more responsive development experience!