getSingleFile abstract method
Get the file from the cache and/or online, depending on availability and age.
Downloaded form url
, headers
can be used for example for authentication.
When a file is cached it is return directly, when it is too old the file is
downloaded in the background. When a cached file is not available the
newly downloaded file is returned.
Implementation
Future<File> getSingleFile(
String url, {
String key,
Map<String, String> headers,
});