[其他]：请问扩展数据到底是什么回事

hantaojian

我是个新手不知道一个实体的扩展数据是什么回事情！请高手指点

stoneball

Inherits From

AcDbObject

Description

The AcDbXrecord class is a data storage class that was implemented primarily to allow ADSRX and AutoLISP programs a means to store data in pieces larger than the xdata's 16KB-per-object limit. Each AcDbXrecord object is capable of storing up to 2GB. By establishing an object's extension dictionary as the xrecord's owner, it's possible to associate large amounts of data with that object.
The input or output mechanism for the data is via a linked list of resbuf structures very similar to the way xdata is accessed on objects. Unlike xdata, however, xrecords work with the standard AutoCAD group codes which are all below 1000 in value. All the standard AutoCAD group codes are supported. This means that, in addition to all the normally used data types, an xrecord is capable of storing object IDs in any of the four types (hard owner, soft owner, hard pointer, soft pointer) which allows xrecords to own other objects, including other xrecords.

Include File

xrecord.h

Tips

AcDbXrecord is a built-in class, so xrecord obects are never proxies. On the other hand, xrecord data is directly accessible by other ADSRX and AutoLISP programs.
If data security is not an issue but always-available data (that is, never a proxy) is an issue, then xrecords are a good solution. If data security is an issue, then a custom data storage class is a better alternative.

See Also

AcDbXrecordIterator

asky333

扩展数据和扩展记录相似。都是基于resbuf结果缓冲区。所增加的数据是字符串的形式。

kfx2002

简单的说就是你可以往实体里存储和你程序有关的数据，之后可以在程序中通过读取这些数据来做你想做的事儿

RedCAD

就是添加额外的数据，比如小王画了一条线，小张画了一个圆，那我们希望程序能记住那条线是小王画的，圆是小张画的，那要实现这样的目的，就需要那样的扩展数据了