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

	compressionRatio	AgoraChatImageMessageBody
	displayName	AgoraChatFileMessageBody
	downloadStatus	AgoraChatFileMessageBody
	fileLength	AgoraChatFileMessageBody
-	initWithData:displayName:	AgoraChatFileMessageBody
-	initWithData:thumbnailData:	AgoraChatImageMessageBody
-	initWithLocalPath:displayName:	AgoraChatFileMessageBody
	localPath	AgoraChatFileMessageBody
-	NS_UNAVAILABLE (定义于 AgoraChatMessageBody)	AgoraChatMessageBody
	operationTime	AgoraChatMessageBody
	operatorCount	AgoraChatMessageBody
	operatorId	AgoraChatMessageBody
	remotePath	AgoraChatFileMessageBody
	secretKey	AgoraChatFileMessageBody
	size	AgoraChatImageMessageBody
	thumbnailDisplayName	AgoraChatImageMessageBody
	thumbnailDownloadStatus	AgoraChatImageMessageBody
	thumbnailFileLength	AgoraChatImageMessageBody
	thumbnailLocalPath	AgoraChatImageMessageBody
	thumbnailRemotePath	AgoraChatImageMessageBody
	thumbnailSecretKey	AgoraChatImageMessageBody
	thumbnailSize	AgoraChatImageMessageBody
	type	AgoraChatMessageBody