Wiley AutoCAD and AutoCAD LT All-in-One Desk Reference For Dummies
Contents
1. Chapter 1 The AutoCAD Programming Interfaces In This Chapter Finding out what programming AutoCAD can do for you Covering the available programming interfaces Mastering the ins and outs of the programming interfaces y Figuring out which programming interface is best for you H ave you ever wanted to create a command alias that represented a specific option of a command Or maybe you have established CAD standards but some of the settings can t be set up through a drawing tem plate alone So you want to make sure the settings are finished before any work on a design begins If so you have come to the right place AutoCAD is more than just a drafting tool Although customizing AutoCAD can help increase productivity by itself the programming interfaces allow you to tap into much more powerful resources that are contained in the depths of AutoCAD Okay saying the resources are in the depths of AutoCAD might be a bit of an exaggeration since they are used every time you run a com mand in the AutoCAD interface This minibook is aimed at AutoCAD users only Sorry AutoCAD LT users the programming interfaces are limited to AutoCAD The supported application programming interfaces APIs for AutoCAD are available after you install AutoCAD or after you ve downloaded them from the Autodesk Web site APIs are used to communicate with the AutoCAD application any open drawing files and objects in a drawing With some of the APIs you2. By logically organized we mean you should understand that objects such as layers aren t just floating around inside a drawing instead they are stored in a table that contains all the layers in a drawing The advantages of using APIs The advantages of APIs differ based on whether you are already using third party applications or add ons for AutoCAD Even if you are you may still dis cover advantages to in house programming Here are some of the benefits for creating custom programs for AutoCAD Accuracy By creating a custom program that runs consistently every time you can increase the accuracy of your drawings If a process has a large number of steps in it some steps might be overlooked This can cause errors to creep into your design Appearance Programming can aid in making drawings look uniform by allowing you to set up drawing options that can t be defined in a drawing template or by allowing you to automate the updating of objects in a drawing Efficiency Repetitive tasks can be speeded up enabling drafters to spend more time on the design process Getting to Know the Available Programming Interfaces 655 Training efficiency Training a new employee is always a challenge If a complex or large set of processes must be followed new employees take even longer to be productive Wrapping custom programs around processes can help get them up and productive in a shorter period of time The downstream effect
3. interface for AutoCAD ActiveX automation ActiveX automation is also known as Component Object Model COM automation COM automation is a form of component based software archi tecture that allows an application to expose its internal functionality in the form of objects COM allows applications to cross communicate with each other to exchange information or interact Many of the modern programming languages like VB VBA C and Java are capable of using COM automation So why is ActiveX automation important in AutoCAD ActiveX automation allows you to use a rich and modern programming language like VB or VBA When you can use a programming language like VB or VBA when communi cating with AutoCAD you can exchange information with data sources like an MS Access database or even an MS Excel spreadsheet This can allow you to improve downstream processes by providing CAD information in different systems to non CAD users who might use the information for billing or manufacturing One of the advantages to using ActiveX automation is that you are not lim ited to just building applications in AutoCAD If you want to develop a stand alone application with VB and communicate with AutoCAD you can If you create a VBA project in MS Word and want to communicate with AutoCAD you can do that too In the remainder of this minibook we discuss ActiveX and VBA as one and the same because VBA uses ActiveX automation Book X Chapter 1 SadePpazu H
4. Being able to get things done faster and more efficiently during the drafting process is great but don t forget about those people who use the data after the design has been completed Custom programming can be used to extract information out of a draw ing or set of drawings that can be useful downstream in manufacturing sales and marketing and many other areas The other side of the story There are always two sides to every story We ve covered some of the bene fits of using the programming interfaces in AutoCAD but there has to bea downside right There is and here are some of the disadvantages to pro gramming in AutoCAD Cost Programming in AutoCAD costs money how much depends on which programming interface you go with These costs might be in the form of software time or consulting fees In the case of a couple of the programming interfaces no additional software packages need to be pur chased but regardless time is always a cost in these types of projects Maintenance AutoCAD changes from release to release When you upgrade to a new version you often have to spend time updating your custom programs Some feature your custom program was using may get broken or you may want to take advantage of a new feature that is introduced to improve a process even further Learning curve Even though a number of the programming interfaces are easy for non programmers to pick up and understand they still require you
5. can create your own custom commands that users can exe cute from the command line The power behind some of these programming interfaces is that you don t need to be a programmer to take advantage of them 65 4 Discovering What Vou Can Do by Programming AutoCAD Discovering What Vou Can Do by Programming AutoCAD You might be thinking to yourself m not a programmer so why do I want to know about programming interfaces The best reason to discover the programming interfaces is to simplify repetitive tasks in your workflow If you can create very basic custom programs that save 15 minutes a day the effort is worth your time especially if you can share these programs with your coworkers Over time your 15 minute savings can grow into much more as you become more efficient with the programming interface Custom programs don t need to be complex to increase efficiency They can be simple like creating new commands that can be used to perform a Zoom Previous from the command line or complicated taking on issues such as CAD standards Managing CAD standards can be a nightmare but the process can be improved by using programming interfaces Tasks such as making sure dimensions are placed on the correct layer can be accomplished if you understand the programming interfaces and how AutoCAD works You don t need to understand how the information is actually written to the file but you do need to know how it is logically organized
6. core functionality of AutoCAD In 1997 Autodesk extended the programming interfaces it was offering to include ActiveX which allowed VB programmers to extend the core func tionality of AutoCAD ActiveX is not just for VB programmers many other mainstream languages such as Java and C support ActiveX so they can interface with AutoCAD Autodesk didn t stop with ActiveX support It kept up with the ever changing landscape of technology and introduced a pro gramming interface for NET that could be used with the new NET languages by Microsoft and other development language vendors AutoLISP AutoLISP is a programming language based on the LISP language LISP stands for list processing It was first introduced back in 1958 and was popular during the 70s and 80s Programmers often joke that the LISP acronym really stands for Lost n Stupid Parentheses Take one look at the code and you might agree LISP uses start and end parentheses for a statement as the following example shows command line 0 0 5 5 In the example you can see the use of the parentheses to start and end the expression The example uses the LINE command to draw a line starting at the coordinate 0 0 and ending at 5 5 As you can see it s not much different from what you are use to typing in at the command line Although not a very powerful statement it is rather easy to understand AutoLISP can be used to organize multiple statements into a custom co
7. amming Most first time AutoLISP programmers feel that it is a much more natural transition into programming because they can use the commands that they are already familiar with to automate tasks It also allows for plenty of growth because it can communicate with other applications using the Visual LISP functions via ActiveX automation AutoLISP is the easiest for beginners to learn and work with Typically VBA is a good fit if you don t really know much about AutoCAD but have a background in VBA or VB programming VBA enables companies with IS departments to get involved with extending AutoCAD because a large number of programmers know VB VBA is a good starting point for begin ners but because you are not using AutoCAD commands the learning curve is higher VBA is a programming interface that both beginners and intermedi ate users can work with NET is the middle of the road option between VBA and ObjectARX Although it requires you to understand one of the newer programming languages such as VB NET or C it isn t as complex as mastering ObjectARX or C Although the NET programming interface does have some limitations in its current implementation it is improving with each new release NET provides some of the simplicity of application development that comes with VBA but has the power of C with a smaller learning curve Although NET is different from VBA the syntaxes look and feel very similar to each other One of the impor
8. d varies slightly AutoLISP has better command line support over VBA because AutoLISP allows you to create custom commands and VBA doesn t If you are looking to offer dialog boxes in your programs you might want to look at VBA over AutoLISP AutoLISP uses a language called DCL Dialog Control Language that defines how a dialog box should look This is different from the other programming languages which use a graphical editor to design the look of dialog boxes ObjectARX has the best support in this area but it also has a number of additional things you have to contend with such as Microsoft Foundation Classes MFC which are tools that help you create robust dialog boxes and user interfaces NET is very flexible in gathering user input but unlike ObjectARX it lacks some control over UI elements that are specific to AutoCAD Maintenance AutoLISP and VBA are the easiest to maintain as they typi cally work on future releases with few changes required ObjectARX pro grams typically need to be rebuilt about every third release of AutoCAD due to binary compatibility issues with the library files NET is a young programming interface for AutoCAD Until it matures you can almost guarantee that any custom programs will need to be rebuilt to some degree between releases In the long term we hope that NET API follows suit with AutoLISP and VBA to reduce the amount of maintenance between releases Longevity AutoLISP has been around t
9. he longest and is the easiest of the four programming interfaces to learn VBA is newer to AutoCAD than AutoLISP but it is nearing the end of its life cycle according to Microsoft This is due to the fact that ActiveX is being replaced by NET which is much newer and more flexible Keep in mind that just because VBA is getting close to the end of its life cycle doesn t mean that support will suddenly stop it will just be slowed down Deciding Which Programming Interface Is Best for You 661 ObjectARX and NET are probably the APIs most likely to be around for a while because they are the ones used by Autodesk ObjectARX seems to have a very bright future but no one ever knows for sure where technol ogy will go Deciding Which Programming Interface Is Best for Vou So which of the four programming interfaces is best for you The two that most users find easiest to use and learn are AutoLISP and VBA which is why we cover them in this book But just because AutoLISP and VBA are covered ae in this book doesn t necessarily make them the right choices for you To determine which option is best for you read the following descriptions of each programming interface and make a decision based on which descrip wee ie tion most closely matches your scenario a2e AutoLISP is a good fit if you know AutoCAD and the commands that are avail S S able to you pretty well or if you don t have much or any experience in pro Z 2 gr
10. ies to tap into an existing development community that knows VB VBA already ObjectARX and Object BX ObjectARX and ObjectDBX are not programming languages like VBA but instead are programming interfaces that allow developers to create and extend AutoCAD using the object oriented C programming language ObjectARX is a collection of library and include files that provides you with the versatility of tools that Autodesk uses to extend the core functionality of AutoCAD and other AutoCAD based products such as Autodesk Architectural Desktop ADT and AutoCAD Mechanical Desktop MDT The vertical products are a collection of ObjectARX programs that are focused on a specific target audience and the type of work they perform ObjectDBxX files are used to define custom drawing objects like the ones found in ADT instead of user interface elements and commands like in ObjectARX files If your programs are calculation intensive you might want to take a look at using ObjectARX for these types of tasks Comparing Strengths and Weaknesses of the Programming Interfaces 65 9 ObjectARX allows for smaller or more compact files faster execution and tighter integration into AutoCAD and Windows Unlike the other program ming options with ObjectARX you need to purchase additional develop ment tools and download the software development kit from the Autodesk Web site When purchasing the development tools you are limited to the version that was used to bu
11. ild the AutoCAD release for which you are creat ing ObjectARX and ObjectDBX programs NET NET is Microsoft s alternative to portable programming languages like Java and J2EE NET represents Microsoft s latest generation of the programming languages that offer flexibility for both application development and usabil pat apter 1 ity To make NET appealing to the development community the develop ment environment Visual Studio NET incorporates more than 20 different languages such as RPG COBOL and C _2o ae The NET programming interface is very similar to the basic concept of g z ActiveX automation but with much greater flexibility through the use of aE newer programming languages and technologies Like ObjectARX a separate ess development environment must be obtained it isn t supplied with AutoCAD However like ActiveX automation the NET API is available upon installing AutoCAD NET help and samples are available as part of the ObjectARX development kit and must be downloaded from the Autodesk Web site Comparing Strengths and Weaknesses of the Programming Interfaces Now that you have an idea of the programming interfaces that are available to use with AutoCAD you ll want to see how they stack up Here we break down some key areas to help you understand how the different program ming interfaces measure up against each other Learning curve If you are not experienced with programming and d
12. m mand that a user can enter at the command line or use in a command macro for a toolbar button To create a new command or a function that can be used to extend the built in AutoLISP functions use the function DEFUN DEfine FUNction Getting to Know the Available Programming Interfaces 657 Although AutoLISP is no longer used as the primary development tool by Autodesk as it once was it is still the primary tool that many users work with because it is easy to learn after you get past all the parentheses As a whole the programming interface is by far one of the most cost effective and forgiving of the four different programming interfaces we discuss in this book The last major update to the AutoLISP programming language was back in 1998 when Autodesk purchased a package called Vital LISP Vital LISP was then renamed to Visual LISP and sold as an add on originally for AutoCAD 14 Visual LISP was then included as part of the AutoCAD 2000 release in 1999 The Visual LISP environment extended the functionality of the AutoLISP lan guage by adding hundreds of functions and allowing AutoLISP to access the AutoCAD Object Model similar to VBA and ActiveX The AutoCAD Object Model is the documented structure of the relationships between AutoCAD and other objects like lines and blocks that are contained in an AutoCAD Drawing file The object model is used as a road map to locate and access the various different objects in the ActiveX programming
13. on t have much time to dedicate to mastering a programming language AutoLISP is the best option for you It is very powerful but doesn t require you to learn a lot of different concepts to get a basic program together If you do have a background in programming you may want to look at using VBA in AutoCAD because it is based on a universal pro gramming language If you have a considerable amount of programming experience you might consider using ObjectARX or NET which take longer to learn but are very powerful NET has far fewer pain points compared to ObjectARX 660 Comparing Strengths and Weaknesses of the Programming Interfaces Execution speed Both AutoLISP and VBA use interpreters to talk to AutoCAD which can cause a lag in execution time and overall execution speed ObjectARX is by far the fastest and most efficient of all the differ ent programming interfaces NET although flexible uses Just In Time JIT compiling which can cause an initial performance lag the first time the program is run Cost AutoLISP and VBA are both built in to AutoCAD so no additional development tools must be purchased ObjectARX and NET require the purchasing of additional tools that can range in price from hundreds to thousands of dollars This might affect which programming interface you use first User input All of the different programming interfaces allow you to get information from a user but how a user s input is collecte
14. tant things that the two share is the capability to use ActiveX automation You could start with VBA and over time transition to NET 662 Deciding Which Programming Interface Is Best for Vou ObjectARX should typically be left up to those who have experience with C because a lot of things can go wrong in a hurry if you don t understand the C programming language In C you are responsible for managing your own memory so if you make a mistake you can develop programs that bring AutoCAD to its knees quickly If you can tame the C programming language beast you will have just about everything you can imagine at your fingertips for creating custom programs in AutoCAD
15. to put in some time if you want to become proficient So before you promise your boss that you can deliver improved productiv ity make sure you are comfortable with the programming language you chose first Getting to Know the Available Programming Interfaces As AutoCAD has evolved over the years so have the different programming interfaces that are available When AutoCAD was first introduced to the world no programming interfaces were built into the application Only about three years after the product was released was the first programming inter face added to the software This programming interface was AutoLISP which Book X Chapter 1 sadepazuy Hurmuweso1g avaoiny ayy 65 6 Getting to Know the Available Programming Interfaces was based on the LISP programming language The introduction of AutoLISP allowed users of AutoCAD to tailor the program for how they wanted to work to improve productivity After AutoLISP came the introduction of ADS AutoCAD Development System which introduced C style coding as a programming option ADS had a rather short life span because the C language was already being overshad owed by the next generation of the C programming language C ADS which was only around for about three years evolved into ObjectARX which is still the premier programming option in AutoCAD 2007 If you look at the install directory of AutoCAD you can see that this is the tool of choice by Autodesk itself to extend the
16. uimuesHo1g avaoiny ayy 65 8 Getting to Know the Available Programming Interfaces VBA VBA Visual Basic for Applications has been around for some time and is an extension of the very popular programming language Visual Basic VB VBA is defined as an object oriented programming OOP language The con cept behind OOP is that a computer program is developed using a collection of individual units or objects as opposed to a listing of instructions Each one of the objects has the ability to receive messages process data and transmit messages to other objects VBA is part of the programming and development tools that are developed by Microsoft Its roots date back to MS DOS and programming languages like QBasic and MS Basic VB has been around longer than VBA and unlike VBA VB can be used to build standalone applications that are not dependent on a host application A host application is a program that allows the VBA environment to run inside it an example of this is AutoCAD Many popular Windows based programs have VBA technology built into them Some of the other applications are Autodesk Inventor AutoCAD based vertical products such as Architectural Desktop ADT and Microsoft Word and Excel VBA in AutoCAD has been a welcomed feature from both the development and non development communities This programming option allows for the integration of business applications directly into the AutoCAD environment and allows compan
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