Vba Redim Preserve Primer Valor

Caroline Mae

2 min read

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01-01-2025

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Understanding how to effectively manage arrays in VBA is crucial for any developer. One powerful tool often overlooked is the Redim Preserve statement. This function allows you to resize an array while preserving the existing values. This is particularly useful when you're dynamically adding or removing elements without wanting to lose your original data. Let's delve into the specifics.

What is Redim Preserve?

In Visual Basic for Applications (VBA), Redim is used to resize arrays. However, a standard Redim will erase the contents of the array, replacing it with empty values. This can be problematic if you've already populated the array with important data. This is where Redim Preserve comes in. It allows you to change the size of a single dimension of an array without losing the data already stored within that dimension.

How Does it Work?

The syntax is straightforward:

Redim Preserve arrayName(newSize)

Where:

• arrayName is the name of your array.
• newSize is the new size you want to assign to the array.

Important Considerations:

• Only One Dimension: You can only resize one dimension of an array using Redim Preserve. If you have a multi-dimensional array (e.g., a 2D array), you can only resize the last dimension. Attempts to resize other dimensions will result in a runtime error.
• Increasing Size: You can only increase the size of the array. Attempting to decrease the size using Redim Preserve will also throw an error.

Practical Example

Let's illustrate with a simple example. Imagine you have an array storing customer names:

Dim customerNames(1 To 5) As String
customerNames(1) = "Alice"
customerNames(2) = "Bob"
customerNames(3) = "Charlie"

Now, you need to add a new customer. Using Redim Preserve, you can expand the array:

Redim Preserve customerNames(1 To 6)
customerNames(6) = "David"

The original values for Alice, Bob, and Charlie are retained, and David is added to the end.

Error Handling

It's crucial to include error handling in your code to gracefully manage potential issues. Always anticipate the possibility of exceeding the maximum array size or attempting to resize an array incorrectly.

Conclusion

Redim Preserve is a valuable tool for efficiently managing arrays in VBA, especially in scenarios where data preservation is crucial. Mastering its use significantly improves code efficiency and reduces the risk of data loss during array resizing operations. Remember the limitations—only one dimension, and only increasing the size—to avoid runtime errors. By incorporating robust error handling, you can ensure your VBA applications are both efficient and reliable.