Скачать или смотреть Resolving Run-time error 13 - Type mismatch in A Class Module Collection in Excel VBA

Discover how to fix `Run-time error 13 - Type mismatch` when accessing items in a class module collection based on keys in Excel VBA.
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Resolving Run-time error 13 - Type mismatch in A Class Module Collection in Excel VBA

If you're working with class modules in Excel VBA and you encounter a Run-time error 13 - Type mismatch when trying to access items based on keys, you're not alone. This issue can be frustrating, especially when your goal is to create a custom collection of objects and access them seamlessly using a specified key. In this guide, we'll explore the root cause of this error and provide clear, step-by-step solutions to resolve it effectively.

Understanding the Problem

When you define a class that includes a collection, you may wish to store multiple instances of that class with each item assigned a unique key. However, you might run into the Run-time error 13 - Type mismatch when trying to access an item in the collection using that key. This often arises due to a mismatch between the expected data type of the key and the way the access method is defined.

The Setup

In the provided case, you have a class tnpObject with properties like Key and Checked, and you're utilizing a collection to hold multiple tnpObject instances. Here's a simplified version of the code snippet causing issues:

[[See Video to Reveal this Text or Code Snippet]]

The problem arises from the way the Index parameter is set. The Item function is currently accepting an Integer as a parameter.

The Solution

Step 1: Change the Parameter Type

To resolve the type mismatch error, you need to adjust the Item function to accept a Variant type instead of an Integer. This change allows the function to handle both integer indices and string keys seamlessly. Here’s the revised code:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Testing Correctly

After making the above adjustment, you can test your class module functions correctly. Ensure to review any test subroutines that utilize the class to fetch items using keys. An example of properly testing the class module would look like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Use Clear Naming Conventions

Using a Variant type allows the function to handle different data types more effectively. Moreover, it's a good practice to clearly comment on your code and its intentions, making it easier for others (and future you!) to understand.

Additional Considerations

Comparison of Function and Property Get: Be mindful of the purpose of each. A function executes a procedure, while a property allows you to get (or set) values of an object's properties. Hence, choose appropriately based on your objectives.

Type of Objects: If you are adding any additional complexity to your class objects, ensure that those are also being defined properly in terms of object types and parameters.

Conclusion

By changing the Item function’s parameter type from Integer to Variant, you effectively resolve the Run-time error 13 - Type mismatch when attempting to access items in your class module collection using keys. This simple change can deliver smoother functionality and help you access your collection more reliably. Don’t hesitate to enhance your code with comments and clear naming conventions to ensure clarity for future reference.

Now that you're equipped with this knowledge, feel free to revisit your code, make the necessary adjustments, and enjoy a smoother development experience with your Excel VBA projects!