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