App Link: Difference between revisions

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(Inheritance section. "File:FreeCAD_core_objects.svg". Simplified diagram of the relationships between the core objects in the program. The App::Link object is a core component of the system, it does not depend on any workbench,)
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== Introduction == <!--T:1-->
== Introduction == <!--T:1-->


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[[File:Link.svg|32px]]
[[File:Link.svg|32px]]
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An [[App_Link|App Link]], or formally an {{incode|App::Link}}, is an element that returns a reference to another object in the document or in an external document. This object was introduced in v0.19 in order to re-use previously created objects, which is very useful to create assemblies.
An [[App_Link|App Link]], or formally an {{incode|App::Link}}, is a type of object that references or links to another object, in the same document, or in another document. It is especially designed to efficiently duplicate a single object multiple times, which helps with the creation of complex [[assembly|assemblies]] from smaller subassemblies, and from multiple reusable components like screws, nuts, and similar fasteners.


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[[File:FreeCAD_core_objects.svg|800px]]
When a regular copy of an object is created (for example, with [[Part SimpleCopy|Part SimpleCopy]]), an entire new object with its topological shape is duplicated, which consumes a lot of memory. App Link is used to re-use existing data of an existing object, so an entire new object doesn't need to be created; this improves the handling of copies, particularly in the context of mechanical assembly where many duplicates may be needed, or where importing smaller assemblies into bigger assemblies is required.


== How to use == <!--T:4-->
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{{Caption|Simplified diagram of the relationships between the core objects in FreeCAD}}


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== Usage == <!--T:4-->
* App Links can be created by pressing {{Button|[[File:Std_LinkMake.svg|16px]] [[Std_LinkMake|LinkMake]]}}.


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See [[Std_LinkMake#Usage|Std LinkMake]].
An [[App_Link|App Link]] is an internal object, so it is mostly intended to be used by developers when developing assembly workbenches. For example, the Assembly3 and Assembly4 workbenches make use of this object. See [[External workbenches|External workbenches]].

==Properties== <!--T:7-->

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See [[Property|Property]] for all property types that scripted objects can have.

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An {{incode|App::Link}} object is not derived from a [[Part_Feature|Part Feature]], however, if the Link has a reference to an external object, it will show the properties of the latter object.

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These are the properties available in the [[property editor|property editor]] for an empty {{incode|App::Link}}.

=== Data === <!--T:11-->

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{{TitleProperty|Link}}
* {{PropertyData|Linked Object}}:
* {{PropertyData|Link Transform}}:
* {{PropertyData|Placement}}:
* {{PropertyData|Show Element}}:
* {{PropertyData|Element Count}}:
* {{PropertyData|Scale}}:

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{{TitleProperty|Base}}
* {{PropertyData|Label}}:

=== View === <!--T:14-->

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{{TitleProperty|Link}}
* {{PropertyView|Draw Style}}:
* {{PropertyView|Line Width}}:
* {{PropertyView|Override Material}}:
* {{PropertyView|Point Size}}:
* {{PropertyView|Selectable}}:
* {{PropertyView|Shape Material}}:

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{{TitleProperty|Base}}
* {{PropertyView|On Top When Selected}}:
* {{PropertyView|Selection Style}}:
* {{PropertyView|Show In Tree}}:
* {{PropertyView|Visibility}}:

== Inheritance ==

[[File:FreeCAD_core_objects.svg|800px]]

{{Caption|Simplified diagram of the relationships between the core objects in the program. The {{incode|App::Link}} object is a core component of the system, it does not depend on any workbench, but it can be used with most objects created in all workbenches.}}

== Scripting == <!--T:17-->

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{{Emphasis|See also:}} [[FreeCAD Scripting Basics|FreeCAD Scripting Basics]], and [[scripted objects|scripted objects]].

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See [[Part_Feature|Part Feature]] for the general information.

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An App Link is created with the {{incode|addObject()}} method of the document.
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{{Code|code=
import FreeCAD as App

doc = App.newDocument()
obj = App.ActiveDocument.addObject("App::Link", "Name")
obj.Label = "Custom label"
}}
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== Further reading == <!--T:21-->


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== Properties == <!--T:32-->
The App Link object was introduced after 2 years of development and prototyping. This component was thought and developed almost single-handedly by user {{Emphasis|realthunder}}. The motivations and design implementations behind this project are described in his GitHub page, [https://github.com/realthunder/FreeCAD_assembly3/wiki/Link Link]. In order to accomplish this feature, several core changes to FreeCAD were made; these were also extensively documented in [https://github.com/realthunder/FreeCAD_assembly3/wiki/Core-Changes Core-Changes].


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See [[Std_LinkMake#Properties|Std LinkMake]].
The App Link project started after the redesign of the [[PartDesign Workbench|PartDesign Workbench]] was complete in v0.17. The history of App Link can be traced to some essential forum threads:
* [https://forum.freecadweb.org/viewtopic.php?f=19&t=21505 Why an object can only be inside one App::Part?] (March 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=10&t=21586 Introducing App::Link/XLink] (March 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=20&t=22216 Links] (May 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=20&t=23015 Realthunder Link implementation: Architecture discussion] (June 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=17&t=23419 PR #876: Link, stage one, context aware selection] (July 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=17&t=23626 Preview: Link, stage two, API groundwork] (July 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=20&t=25712 Assembly3 preview] (December 2017)
* [https://forum.freecadweb.org/viewtopic.php?f=10&t=29542 Merging of my Link branch] (June 2018)


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Finally, the pull request and merge happened:
* [https://forum.freecadweb.org/viewtopic.php?f=27&t=38621 App::Link: the big merge], old thread (July 2019), [https://github.com/FreeCAD/FreeCAD/pull/2350 pull request #2350] (the BIG merge), [https://github.com/realthunder/FreeCAD/tree/LinkMerge LinkMerge branch].
* [https://forum.freecadweb.org/viewtopic.php?f=8&t=37757 App::Link: the big merge], main thread (July 2019)
* [https://forum.freecadweb.org/viewtopic.php?p=329054#p329054 A simple path description of Link, 019, Link stage, Asm3, merge?] (August 2019)
* [https://forum.freecadweb.org/viewtopic.php?f=17&t=39672 PR#2559: expose link and navigation actions], an introduction to the Link feature in 0.19 (September 2019).


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Latest revision as of 07:42, 22 February 2022

Introduction

An App Link, or formally an App::Link, is a type of object that references or links to another object, in the same document, or in another document. It is especially designed to efficiently duplicate a single object multiple times, which helps with the creation of complex assemblies from smaller subassemblies, and from multiple reusable components like screws, nuts, and similar fasteners.

Simplified diagram of the relationships between the core objects in FreeCAD

Usage

See Std LinkMake.

Properties

See Std LinkMake.