Autocad允许应用程序在实体对象上附加XDATA（扩展数据）。XDATA可以附在任何图形实体以及层，线型等非图形实体上，Autocad负责维护这些信息，但不使用这些信息，也不在图纸中直接表现出来。XDATA的每一组均以一个互相不相同的应用程序名开头，组码在1000~1071之间，不同组码对应不同类型的信息。

Autocad提供的这个特性，为应用程序提供了极大的方便，在开发零件序号标注，图框绘制，自动拼图等应用程序时，均利用了XDATA来识别实体的身份，位置，保存图幅，比例等信息供程序使用。

import sys
sys.path.append(r‘E:\programming\PycomCAD‘)
from pycomcad import *

acad=Autocad()

rapps=acad.acad.ActiveDocument.RegisteredApplications

rapps是图形对象的注册应用（registered applications)的集合，它有Add(),Item()方法，当用Add()方法时候，就像该集合添加了一个应用，选择某个特定的app用Item()方法。

rapps.Count

71

rapps.__class__

win32com.gen_py.D5C3CB6F-AA0A-4D45-B02D-CF2974EFD4BEx0x1x0.IAcadRegisteredApplications

以下代码可用以增强RegisteredApplication类的用法：

class rappSpecial(rapps.__class__):
    @property 
    def appNames(self):
        names=[]
        for item in range(self.Count):
            names.append(super().Item(item).Name)
        return names
    def Item(self,item):
        print(‘intercepting‘)
        if isinstance(item,int):
            return super().Item(item)
        if isinstance(item,str):
            return super().Item(self.appNames.index(item))           

rappSpecial(rapps).Item(0).Name

intercepting

‘ACAD‘

rappSpecial(rapps).Item(‘ACAD‘).Name

‘ACAD‘

rappSpecial(rapps).Count

43

for index in range(rapps.Count):
    app=rapps.Item(index)
    print(app.Name)
    print(app.GetXData(‘‘))

ACAD
(None, None)
ACAD_PSEXT
(None, None)
AcadAnnotative
(None, None)
ACAD_DSTYLE_DIMJAG
(None, None)
ACAD_DSTYLE_DIMTALN
(None, None)
ACAD_NAV_VCDISPLAY
(None, None)
ACAD_TEMP_GRAPHIC
(None, None)
DESIGNERASSEMBLIES
(None, None)
ACAD_DSTYLE_DIMBREAK
(None, None)
AcAecLayerStandard
(None, None)
GENIUS_GENBH_13
(None, None)
GENIUS_GENOENT_13
(None, None)
GENIUS_GENODEF_13
(None, None)
GENIUS_GENOREF_13
(None, None)
GEVID1390703250
(None, None)
GENIUS_GENDTOL_13
(None, None)
ACAD_DSTYLE_DIMRADIAL_EXTENSION
(None, None)
GENIUS_GENREC_14
(None, None)
GENIUS_GENOBJ-N-CEN_13
(None, None)
GENIUS_GENOBJ-N-CRC_13
(None, None)
GENIUS_GENSCREG_15
(None, None)
GENIUS_GENOBJ-N-SDF_13
(None, None)
ACCMTRANSPARENCY
(None, None)
GEVID1474596514
(None, None)
ACM_PP_ASSOCVAR
(None, None)
ACM_PP_DIM_CONSTRAINT_DRAG_GRIP
(None, None)
GEVID1474596516
(None, None)
GEVID1474682654
(None, None)
GEVID1474682656
(None, None)
GEVID1474682658
(None, None)
GEVID1474682660
(None, None)
GradientColor1ACI
(None, None)
GradientColor2ACI
(None, None)
AcDbDynamicBlockGUID
(None, None)
AcDbBlockRepETag
(None, None)
AcDbDynamicBlockTrueName2
(None, None)
ACAD_OBJECT_NAME
(None, None)
ACAD_NETWORK_GROUPS
(None, None)
ACAD_DSTYLE_DIM_LINETYPE
(None, None)
ACAD_DSTYLE_DIM_EXT2_LINETYPE
(None, None)
AcDbAttr
(None, None)
CAXA_DRAFT_TXTSCALE
(None, None)
test
(None, None)

p=rapps.Add(‘today20210619‘)

p.SetXData(FilterType([1001,1000,]),FilterData([‘test‘,‘this is a test in 2021‘]))

rapps.Item(74).GetXData(‘‘)

((1001, 1000), (‘test‘, ‘this is a test in 2021‘))

对XData进行构造和读取，只用：
SetXData(XdataType,Xdata),
GetXData(AppName,XDataType,XdataValue)，
用pycomcad内置的方法就是acad.SetXData(entity,xdataPairs)

p=acad.GetEntity() #拾取实体

acad.SetXData(p[0],[(1001,‘test‘),(1000,‘this is an example‘)])

p[0].GetXData(‘‘)

((1001, 1000), (‘test‘, ‘this is an example‘))

p[0].GetXData(‘test‘)

((1001, 1000), (‘test‘, ‘this is an example‘))

Autocad二次开发中的XData