readFile method
Reads a file from assets folder.
Implementation
Future<String> readFile(String fileName, {String? package}) async {
final cacheKey = package == null ? fileName : 'packages/$package/$fileName';
if (!_files.containsKey(cacheKey)) {
_files[cacheKey] = await _readFile(fileName, package: package);
}
assert(
_files[cacheKey] is _StringAsset,
'"$cacheKey" was previously loaded as a binary file',
);
return (_files[cacheKey]! as _StringAsset).value;
}