v2::V2NIMDownloadMessageAttachmentParams 成员列表

成员的完整列表，这些成员属于 v2::V2NIMDownloadMessageAttachmentParams,包括所有继承而来的类成员

attachment	v2::V2NIMDownloadMessageAttachmentParams
messageClientId	v2::V2NIMDownloadMessageAttachmentParams
saveAs	v2::V2NIMDownloadMessageAttachmentParams
thumbSize	v2::V2NIMDownloadMessageAttachmentParams
type	v2::V2NIMDownloadMessageAttachmentParams