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Learn how to fix the 'Conversion from String to type Long' error in VB.NET while displaying message boxes using dropdown selections.
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This video is based on the question https://stackoverflow.com/q/63523608/ asked by the user 'Lord45' ( https://stackoverflow.com/u/9599896/ ) and on the answer https://stackoverflow.com/a/63523747/ provided by the user 'Anu6is' ( https://stackoverflow.com/u/11159372/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the Conversion from String to type 'Long' Error in VB.NET Message Boxes

When working on a programming project, encountering errors can be frustrating, particularly when you are transitioning from one language to another. If you are rewriting an older program from VBA to VB.NET, you may come across issues that are not immediately apparent. One common problem you might face is the Conversion from String to type 'Long' is not valid error, especially when displaying messages with the MessageBox.Show function. In this guide, we’ll delve into this issue and provide you with a step-by-step solution to streamline your code.

The Problem

While rewriting your VBA code into VB.NET, you may have a For loop structure designed to ensure that selections made in dropdowns do not conflict. During this process, you might encounter the error message stating that a conversion from String to Long is not valid. Here's a brief overview of the situation:

You have two arrays (TCi and TCj) containing temperature channel names.

A loop is used to check whether selections in dropdowns match those arrays.

Errors occur when trying to display a message box with the selected values, specifically when concatenating strings.

The specific lines that trigger the error typically look like this:

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

The Solution

1. Understanding Concatenation in VB.NET

In VB.NET, string concatenation is done using the & operator, which is similar to what you may have used in VBA with &. However, the version in your code might mislead VB.NET into treating certain components of your message as numeric values instead of strings.

2. Fixing the Code

To clarify the syntax and avoid misunderstandings with data types, here’s the corrected way to implement the MessageBox.Show function. Instead of including a space after "temp for" in the wrong place, do it right within the string construction:

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

3. Example of the Complete Message Box Code

The following is an corrected example of how to set up your message box displays that should eliminate the conversion issue:

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

4. General Code Best Practices

Always ensure that concatenations are clear and that any variables you are using are appropriate for their data types.

Avoid unnecessary spaces embedded within your string concatenations unless needed, as they might confuse the compiler.

Keep your arrays organized and clearly comment your code to ease future transitions or debugging.

Conclusion

When converting from VBA to VB.NET, small discrepancies in syntax can lead to perplexing errors. The Conversion from String to type 'Long' is not valid issue is one such example but can be easily resolved by correcting your string concatenation in MessageBox.Show. With the adjustments provided in this guide, you should be able to display message boxes without hiccups, enhancing the functionality of your application.

If you have further questions or need clarification on your VB.NET code, feel free to ask or share your code snippets for additional support!