Flr (Flutter-R): a CLI tool likes AAPT(Android Asset Packaging Tool), which can help flutter developer to auto specify assets in pubspec.yaml and generate R.dart file after he changes the flutter project assets. With R.dart, flutter developer can apply the asset in code by referencing it's asset ID.

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• Support auto service that automatically specify assets in pubspec.yaml and generate R.dart file, which can be triggered manually or by monitoring asset changes
• Support for processing image assets ( .png, .jpg, .jpeg, .gif, .webp, .icon, .bmp, .wbmp, .svg )
• Support for processing text assets ( .txt, .json, .yaml, .xml )
• Support for processing image asset variants
• Support for processing asset which’s filename is bad:
  • filename has illegal character (such as blank, ~, @, # ) which is outside the range of valid characters (0-9, A-Z, a-z, _, $)
  • filename begins with a number or character _ or character$

To install or update Flr, run sudo gem install flr

If you want to use Flr tool on the Windows system, you are strongly recommended to run it on WSL(Windows Subsystem for Linux) environment !!!

To uninstall Flr run sudo gem uninstall flr

1. Init your flutter project:

   cd flutter_project_dir
   flr init
   

   The flr init command generates Flrfile.yaml file and specifies package r_dart_library in pubspec.yaml for project.

   Attention:

   The Flutter SDK is currently in an unstable state, so if you get a build error of r_dart_library , you can fix it by modify the dependent version of r_dart_library.

   You can select the correct version of r_dart_library based on this dependency relationship table.

2. Open Flrfile.yaml file, and edit it according to the prompts in the file to configure the asset directory paths that needs to be scanned by Flr, such as:

    assets:
    
      # config the image asset directories that need to be scanned
      # supported image assets: [".png", ".jpg", ".jpeg", ".gif", ".webp", ".icon", ".bmp", ".wbmp", ".svg"]
      # config example: - lib/assets/images
      images:
        - lib/assets/images
    
      # config the text asset directories that need to be scanned
      # supported text assets: [".txt", ".json", ".yaml", ".xml"]
      # config example: - lib/assets/texts
      texts:
        - lib/assets/jsons
        - lib/assets/yamls
   

3. Monitor the asset changes and auto specify assets and generate R.dart for your flutter project:

   flr monitor

   The flr monitor command launches a monitoring service that continuously monitors asset changes for your project.

   The monitoring service monitors the asset directories configured in Flrfile.yaml, and if it detects any asset changes, it will automatically execute flr generate command which will perform a assets scan for the asset directories configured in Flrfile.yaml, then automatically specifies scanned assets in pubspec.yaml, and generates R.dart file.

   You can terminate this monitoring service by manually pressing Ctrl-C.

4. Press Ctrl-C to terminate the monitoring service if you want.

If you want to manually trigger the auto service which can automatically specify assets and generate R.dart for your flutter project, you can run this command:

flr generate

The flr generate command does once a assets scan for the asset directories configured in Flrfile.yaml, then automatically specifies scanned assets in pubspec.yaml, and generates R.dart file.

Attention: all commands MUST be runned in your flutter project root directory.

After you run flr generate or flr monitor, Flr will automatically scan the assets based on the asset directory configuration in Flrfile.yaml, then specify scanned assets in pubspec.yaml, and generate the R.dart file.

R.dart defines several R_X asset management classes: R_Image, R_Svg, R_Text. These asset management classes are used to manage the asset IDs of the respective asset types:

• R_Image: manage the asset IDs of non-svg type image assets ( .png, .jpg, .jpeg, .gif, .webp, .icon, .bmp, .wbmp )
• R_Svg: manage the asset IDs of svg type image assets
• R_Text: manage the asset IDs of text assets ( .txt, .json, .yaml, .xml )

R.dart allows flutter developer to apply the asset in code by referencing it's asset ID. Here are some simple examples:

import 'package:flutter_r_demo/R.dart';

// sameName.png
var normalImageWidget = Image(
  width: 113,
  height: 128,
  image: R_Image.sameName,
);

// sameName.gif
var gifImageWidget = Image(
  image: R_Image.sameName_gif,
);

// $$test$.svg
var svgImageWidget = Image(
  width: 100,
  height: 100,
  image: R_Svg.a$$test$(width: 100, height: 100),
);

// $%^&test.json
var jsonString = await R_Text.a$___test_json();

// ~!@*test.yaml
var yamlString = await R_Text.a____test_yaml();

Here is a Flutter-R Demo to show how to use Flr tool in flutter project and show how to use R.dart in your code.

The gem is available as open source under the terms of the MIT License.