what is the use of _AcDb.Handle.IsOne

[essam-salah]

Hi,

as its a self described title i want to know a use case for _AcDb.Handle.IsOne  ?

thanks in advance

[BlackBox_]

https://help.autodesk.com/view/OARX/2023/ENU/?guid=OARX-ManagedRefGuide-Autodesk_AutoCAD_DatabaseSer...

There isn't much use for Handle == 1 (or Entity 0). 

[essam-salah]

@BlackBox_ 

i already read the documentation, another question can we know if the object exists or not using Handle ?

[_gile]

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@essam-salah  a écrit :

can we know if the object exists or not using Handle ?

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You can use the undocumented Database.TryGetObjectId method.

Signature:

public bool Autodesk.AutoCAD.DatabaseServices.Database.TryGetObjectId(
    Autodesk.AutoCAD.DatabaseServices.Handle objHandle, 
    out Autodesk.AutoCAD.DatabaseServices.ObjectId id)

[essam-salah]

@_gile 

thanks for the post, so how to check if the Id is exist?

[_gile · Accepted solution]

TryGetObjectId returns true, if the supplied Handle is bound to an ObjectId (and set this ObjectId to the out parameter); false, if the supplied Handle is not bound to an ObjectId (and set the out parameter to OnjectId.Null).

[daniel_cadext]

It’s probably something internal, since it’s been around forever,A handle of One seems to always point to the AcDbBlockTable

“since all databases start with the same handseed value of 1 and go up from there”

I also wonder the purpose of mLow and mHigh?  Maybe to increase the address range back in the days of 16bit computers  

Sorry if I went off topic

[artc2]

Handles are 64-bit. mLow and mHigh are to allow 64-bit handles on 32-bit computers.

[daniel_cadext]

Ah, that make more sense