showFilePicker method
Implementation
@override
Future<List<String>> showFilePicker(List<String> allowedExtensions,
{bool pickMultiple = false}) async {
//conver the list to a string like *.jpg;*.png;vlc.exe
String allowedExtensionsString = allowedExtensions.join(';');
final List<dynamic> result = await _channel.invokeMethod(
'showFilePicker', <String, dynamic>{
'allowedExtensions': allowedExtensionsString,
'pickMultiple': pickMultiple
});
return result.cast<String>();
}