Blog 5.10.2012 6 Comments

For those who don’t know,, the largest CAD/CAM blog in the world, recently ran an article on in which I answered three questions about the SolidWorks API. The third question was perhaps the most insightul: “What advice do you have for aspiring API progammers?” This question is so important that I decided to expand upon my answer in more depth in this blog post.

Even though this post is geared toward beginners, those who have many macros under their belt but still don’t quite feel like they’ve “got it” should find great insight. So without further adieu, here are 7 warnings I offer to every engineer who wants to program seriously with the SolidWorks API.

1. Not learning the SolidWorks API with Visual Basic for Applications (VBA)

VB.NET, C#, and C++ are very powerful languages. However, for macros of low to medium complexity, that power is completely unnecessary. If you’re an aspiring API programmer, you probably care about just one thing: automating your work. Then why fight the steeper learning curve of those other languages? Learn the API with VBA so you can spend less time learning the programming language itself and more time learning the SolidWorks API. The API works roughly the same in each language, so once you’re ready to move on to a more complex language, you already have the important stuff under your belt.

Ready to learn VBA programming basics? Check out the free lessons from Unit 1 of our VBA course.

2. Relying On the Macro Recorder

For an API novice, it makes perfect sense to use the macro recorder. Here’s a tool, it would seem, that gives you all of the API calls you need to create a macro. Right? Wrong. For starters, the macro recorder can’t record certain tasks at all. Working with custom properties is an example. Second, relying on the macro recorder is dangerous because keeps you in the mindset that the API performs tasks the same way you would perform them “manually”. Again, this couldn’t be further from the truth. The steps required to create a section view or change a face’s color, for example, are entirely different when using the API versus using SolidWorks normally. Third, the code the macro recorder produces is incredibly sloppy. Its formatted poorly and typically contains arguments you may or may not want. A much better practice is to use the macro recorder to “discover” an API call when you know it might take a while to find in the API Help. Nevertheless, the API Help, not the macro recorder, should be your ‘go-to’ resource, as we’ll discuss in the next mistake.

Want to learn more about the uses and limitations of the macro recorder? Check out Lesson 2.1 in our VBA course.

3. Not understanding how to use the API Help

If you think the API Help is just a stuffy reference for hardcore developers, think again. If you don’t know how to navigate your way around the API Help, your macros will never move beyond what you create with the macro recorder or what you copy and paste from someone else’s code. Using the Index tab of the local API Help, you can search topically until you find the API call or interface you need. Every single API call and interface has its own page describing how to use it properly—from arguments to return values to examples to other useful tidbits of info that you need to know.

Ready to learn how to use the API Help? Check out Lesson 2.2 from our VBA course.

4. Not understanding the SolidWorks API object model

If you really want to go to the next level as an API programmer, you MUST understand the SolidWorks API Object Model. What is this “object model”, you ask? Basically, everything you interact with in SolidWorks is considered an object by the SolidWorks API—a face, an edge, a drawing view, a component, the FeatureManager tree, a part document, the SolidWorks application itself, and so on. Each of these objects has a corresponding “interface” that lets the API talk with that object. Now here’s the important part: these objects are arranged in a hierarchy. So, for example, before you can change the color of a face, you need access to that face’s body. Before you have access to the body, however, you need access to the part document. Before you have access to the part document, you need access to the SolidWorks application. Get the idea?

To access different interfaces you need to use special API calls known as “accessors”. Here’s the great thing: every interface page in the API Help has a list of the accessors that can be used to access that interface. Hence the importance of knowing how to use the API Help well.

Ready to learn the SolidWorks API Object Model in conjunction with the API Help? Check out Lesson 2.3 from our VBA course.

5. Not modularizing your code

Modularizing code allows you to easily re-use code. It also makes you a faster programmer and makes your code less error-prone. Let me explain. Say that you write lots of macros that require you to pull out the value of a custom property called “PartNo”. Instead of re-writing that bit of code over and over again, you should create a separate function (called something like “GetPartNo”) that is called by your main code. Once you’ve written “GetPartNo” once, you don’t need to keep writing it. Instead you can place that function in its own module that you can import easily to other macros. Since you know it works, you don’t have to worry about debugging it in the future.

Ready to learn how to modularize your code? Check out Lesson 1.7 from our VBA course.

6. Not documenting or formatting your code properly

This isn’t just a mistake committed by API programmers but programmers in general. However the mistake is so serious that I have to mention it again, even if you’ve heard it before: take the time to format and document your code properly. Formatting code properly means using appropriate indentation when you “nest” layers of code within sub-procedures, conditional statements, loops, and so on. By not doing this you are making your code very difficult to read.

Documenting your code means using comments to explain the purpose of each section of code. For example, if you check out any of the macros in our Macro Library, you’ll notice three things: 1) at the top, an explanation of what the code does (including preconditions necessary for running the code), 2) comments throughout the macro explaining what role each portion of code plays, and 3) often times at the time you’ll see additional notes giving more insight into a certain API call. The result is code that is much easier for the author and others to understand. If you don’t believe me, just wait until you have to edit a macro that you wrote two years ago. You’ll have no clue what the variables do and will have to spend a large portion of time re-familiarizing yourself with the code. Its even worse if you weren’t the one who wrote the code originally.

Ready to learn more about formatting and documenting code? Check out the first four lessons of our VBA course, or check out our one-hour intro to the API, Taking Macros to the People.

7. Giving up too quickly

As with anything else in life that’s worth doing, becoming a good SolidWorks API programmer requires perseverance. As a programmer, you’re going to hit obstacles constantly. With every obstacle, however, is the opportunity for another victory. Learn to love these small victories. Keep your eye fixed on prize—automating your project, impressing your co-workers, expanding your professional repertoire, or whatever it might be. Again, as with anything else that’s challenging, programming with the API gets easier as you practice it more. Once you understand the API Help and Object Model, you’ll truly be amazed at how quickly you can write macros. You’ll love it! So stick with it, and enjoy the results.

Whether you’re a novice presently committing these mistakes or an expert that has long moved past them, I’d love to hear your insight! Share in the comments below.


Want to stay up-to-date with new content? Sign up for our newsletter.


  1. jsweeney

    Not a “mistake”, but one that burns me reading code by someone that uses variable names that have no meaning.

    Another one on the same line…and SW help files are bad at this. Using different variable names from one program to another. Sometimes they’ll use swView, others oView, etc. It makes it hard to reuse code. If you always use the same variable name for a view, cutting and pasting from one program to another is much faster.

    • That’s a good point. Perhaps I should add something on variables to point 6.

      In CADSharp’s macro library, we use the same variable names consistently for exactly the reason you described.

  2. […] Without the proper foundation, learning the SolidWorks API can be nothing short of frustrating. As a self-taught SolidWorks API programmer, here’s 7 pieces of advice I want to offer to help you on your learning journey. These guidelines are adapted from 7 Mistakes New SolidWorks API Programmers Make. […]

  3. 4ubarkoIIi

    When I started to learn SolidWorks API (6 months ago) I read this article.
    However, I didn’t put much attention to some points. I ask anyone who wants to start his own way to keep in mind my mistake! It definetely will safe a lot of hours for you!
    Eventually, after a lot of hard working the seven point will mean a lot to you!

  4. dodle

    how do you ensure that your macros will stay working….
    I just lost one that I have been trying to figure out for a week

  5. Someone told me that when using the CATIA API to return the model features, they were able to see the model names as strings in the array. They wanted to know how to do the same in the SolidWorks API and whether this required moving to .NET from VBA. My response:

    1. I have never used the CATIA API, but the reason you can see the names of the feature tree when using the Watch or Locals Window is probably because the object returned is actually an array of strings, whereas in the SolidWorks API, methods like IFeatureManager::GetFeatures returns an array of objects.

    2. In VB.NET you will not be able to see the names either. Again, this is because the feature manager tree object is not simply a collection of strings.

    3. In VBA and/or VB.NET you should print the names of the feature manager tree to the immediate/debug window if you wish to see the names. Look at IModelDoc2::FirstFeature in the API Help to see examples.

Questions and Comments

You must be logged in to post a comment.