Visual Basic for Applications (VBA) is an implementation of Microsofts event-driven programming language Visual Basic 6 and its associated integrated development environment (IDE). VBA enables building user-defined functions, automating processes, and accessing Windows API through Microsoft Office applications.
VBA Anti-Patterns Overview
Visual Basic for Applications (VBA), despite being a powerful tool for Microsoft Office automation, has several common anti-patterns that can lead to maintainability problems, performance issues, and bugs. Here are the most important anti-patterns to avoid when writing VBA code.
Using Select/Activate in Excel VBA
Avoid using Select and Activate methods in Excel VBA. These methods are slow, can be affected by user selection, and make code harder to maintain. Instead, use direct object references to manipulate ranges and other objects.
Using Global Variables Excessively
Avoid excessive use of global variables. They create hidden dependencies between procedures, make code harder to test and maintain, and can lead to unexpected behavior. Instead, pass parameters between procedures and use local variables when possible.
Not Using Option Explicit
Always use Option Explicit
at the top of your modules to force explicit variable declaration. This prevents typos in variable names from creating new variables, which can lead to hard-to-find bugs.
Using On Error Resume Next Without Proper Error Handling
Avoid using On Error Resume Next
without checking for errors afterward. This suppresses all errors but doesn’t handle them, which can lead to unexpected behavior. Instead, use structured error handling with On Error GoTo
and handle specific error cases appropriately.
Hardcoding Ranges and Values
Avoid hardcoding ranges, cell addresses, and magic numbers in your code. Instead, use named ranges, constants, and dynamic range determination. This makes your code more maintainable and adaptable to changes in the worksheet structure.
Inefficient Worksheet Loops
Avoid inefficient worksheet interactions, especially in loops. Reading from or writing to worksheets is much slower than working with variables in memory. Use arrays to store and manipulate data, then update the worksheet in a single operation. Also, turn off screen updating during intensive operations to improve performance.
Not Using Proper Data Types
Use appropriate data types instead of relying on Variant. Variants are flexible but consume more memory and can be slower than specific data types. Use Integer or Long for whole numbers, Double for decimal numbers, String for text, and Boolean for true/false values.
Not Using With Blocks for Multiple Property Settings
Use With
blocks when setting multiple properties of the same object. This makes your code more readable and can improve performance by reducing the number of times the object needs to be evaluated.
Using Macros for Simple Formulas
Avoid using VBA for calculations that can be done with Excel formulas. Excel’s built-in formulas are optimized for performance and recalculate automatically when data changes. Use VBA for tasks that can’t be easily accomplished with formulas, such as complex logic, file operations, or user interface interactions.
Not Structuring Code into Procedures
Break down large, monolithic procedures into smaller, focused procedures and functions. Each procedure should have a single responsibility. This makes your code more readable, maintainable, and reusable.
Not Using Early Binding When Appropriate
Consider using early binding (setting references and declaring specific object types) when working with external applications like Word or Outlook. Early binding provides IntelliSense, compile-time type checking, and better performance. However, late binding (using Object type and CreateObject) can be more flexible when you need to support different versions of the external application.
Not Using Proper String Concatenation
Avoid repeatedly concatenating strings in a loop using the &
operator, as this creates a new string object each time. Instead, use the StringBuilder pattern (collecting strings in an array and joining them at the end) or use the Join
function for better performance with large strings.
Not Using Proper Loop Constructs
Use the appropriate loop construct for each situation. Use For
loops when you know the number of iterations in advance, For Each
loops when iterating through collections, and Do While
or Do Until
loops when you need to continue until a condition is met.
Not Using Proper Code Comments
Use meaningful comments to explain why your code does something, not what it does (which should be clear from the code itself). Include comments for procedure purposes, complex logic, and any non-obvious decisions. Also, use meaningful variable and procedure names to make your code self-documenting.
Not Using Proper Workbook and Worksheet References
Use explicit workbook and worksheet references instead of relying on the active workbook or worksheet. This makes your code more reliable and less dependent on the user’s current selection. Use ThisWorkbook
to refer to the workbook containing the code, and declare worksheet variables for clarity.
Not Using Proper Application Settings
Properly manage application settings like ScreenUpdating, EnableEvents, and Calculation to improve performance during intensive operations. Always save the original settings and restore them when your procedure finishes, even if an error occurs.