如何创建一个水晶报表用户自定义函数库 UFls (Creating a Crystal Reports Custom Function Library)

 Creating a Crystal Reports Custom Function Library

You don't always have to massage your data with complex formulas to report on it. Complex calculations in a report can be difficult at times. Not only that, but can cause your report to run unbearably slow. Custom function libraries allow you to pull the complex calculations & functions out of the report and in to an environment where you can better control their output.

I originally wrote this article in 1999 for another publication focused on Visual Basic. I am posting this here by request. The concepts described here still apply to building custom function libraries for Crystal Reports today. The article discusses building custom function libraries using Visual Basic 6, although see the comments at the end of an article for details about doing this from .NET and deploying via .NET Extensions.

Crystal Reports allows you to create custom function libraries with little effort. These custom libraries, known as User Function Libraries (UFL), have been an option since even some of the earliest versions of Crystal Reports. Custom DLL's could be created which extended Crystal's libraries. However, these DLL's were impossible to create in Visual Basic due to the complex specifications for the DLLs and limitations in Visual Basic. The original SDK for creating a UFL was developed mainly for C programmers and is still provided on the Crystal Reports CD. However, this tutorial is going to take a much easier approach.


Extending Crystal Reports via COM

Since version 6 of Crystal Reports, Seagate extended the ability of creating a UFL to any language that can create a COM application. Creating COM applications in Visual Basic is a breeze since the VB IDE does most of the work for us. By creating a UFL COM application you are able to extend the functionality of Crystal Reports and greatly enhance your reports. Remove complex functions from your report and put it in a COM application. You save yourself a headache by not having to find some tricky way to implement the function, but also your report may run faster by allowing the function to run as compiled code. The functions from your UFL are access