Flutter asset loading error: No file or variants found for asset

No file or variants found for asset is an error that prevents running the Flutter app when the assets path are not defined properly. The following are some common causes:

As an example, here is a project root files and folders structure. The assets folder and it’s sub-folder images and json are manually created after project initialization. The assets folder is named with assets, but it can be any other names, as well as the sub folders inside it, they can be any other names.

┬
└ project_name
  ┬
  ├ android
  ├ assets     - This folder its sub-folders does not come from project initialization.
    ┬
    └ images/
    └ json/          
  ├ build        
  ├ ios          
  ├ lib          
    ┬
    └ src        
    └ main.dart  
                   
                    
                   
  ├ test         
  └ pubspec.yaml 

In order for Flutter to recognize the asset folder, its sub folders, image or json files. The path to those folders that you created has to be defined in the pubspec.yaml file.

flutter
  assets:
    - assets/images/
    - assets/json/

If there is a json file data.json in assets/json/data.json, it can be loaded like this. The file path in rootBundle.loadString starts from the project root folder.

import 'package:flutter/services.dart';

final String response = await rootBundle.loadString('assets/json/data.json');
final data = await json.decode(response);
print(data);