OfflineController constructor
Implementation
OfflineController() {
  _channel = MethodChannel('flutter_bmfmap/offlineMap');
  _bmfOfflineMapDispatcher = BMFOfflineMapDispatcher();
  _channel.setMethodCallHandler(_handlerMethod);
}
    OfflineController() {
  _channel = MethodChannel('flutter_bmfmap/offlineMap');
  _bmfOfflineMapDispatcher = BMFOfflineMapDispatcher();
  _channel.setMethodCallHandler(_handlerMethod);
}