DownloadTask.fromJson constructor
Creates DownloadTask object from json
Implementation
DownloadTask.fromJson(super.json)
: assert(
['DownloadTask', 'ParallelDownloadTask'].contains(json['taskType']),
'The provided JSON map is not'
' a DownloadTask, because key "taskType" is not "DownloadTask" or "ParallelDownloadTask".'),
super.fromJson();