topic entity type in ObjectARX Forum

entity type

johnteng00 — Mon, 10 May 2021 13:29:42 GMT

Hi guys,

I use c++. When user select an entity, I want to find out the entity type.

Certainly I can use: AcDb3dSolid::cast(obj) or similar approach to find the right type I need. But I want to know is there are other ways to find the entity type.

Thank you

Eric

回复： entity type

hbxiaogui — Tue, 11 May 2021 00:26:33 GMT

ent->isA()==AcDb3dSolid::desc() ent->isKindOf(AcDb3dSolid::desc())

回复： entity type

johnteng00 — Tue, 11 May 2021 02:02:27 GMT

good, thank you for your reply.

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tbrammer — Tue, 11 May 2021 09:42:04 GMT

You can also use AcRxClass* AcDbObjectId::objectClass() const to query the class from the AcDbObjectId without even opening the object.

Sometimes you might also want to test for a base class:

ent->isDerivedFrom(AcDbDimension::desc())

This would be true if ent is any kind of dimension.

回复： entity type

autodaug — Thu, 13 May 2021 14:52:11 GMT

Just to clarify, isKindOf() is a method of AcRxObject, while isDerivedFrom() is a method of AcRxClass. So the method you want to call depends on whether you're pointing to the entity or to its class object. If ent points to an AcDbEntity and id is its AcDbObjectId, then you can check for it being a dimension in these ways:

ent->isKindOf(AcDbDimension::desc()) // or: ent->isA()->isDerivedFrom(AcDbDimension::desc()) // or: id.objectClass()->isDerivedFrom(AcDbDimension::desc())

And to make it more confusing, AcRxClass itself is derived from AcRxObject, so it's possible, although usually incorrect and unintended, to do this:

id.objectClass()->isKindOf(AcDbDimension::desc())

That will always return false because objectClass() returns a pointer to an AcRxClass object, and AcRxClass itself is not derived from AcDbDimension. It derives directly from AcRxObject.