{"id":128,"date":"2008-07-07T04:01:00","date_gmt":"2008-07-07T04:01:00","guid":{"rendered":"\/lisa\/post\/2008\/07\/07\/The-scoop-on-scoping-FRX-variables-and-the-first-officially-recorded-instance-of-the-Duke-Principle.aspx"},"modified":"2021-08-30T13:38:47","modified_gmt":"2021-08-30T20:38:47","slug":"the-scoop-on-scoping-frx-variables-and-the-first-officially-recorded-instance-of-the-duke-principle","status":"publish","type":"post","link":"https:\/\/spacefold.com\/lisa\/2008\/07\/07\/the-scoop-on-scoping-frx-variables-and-the-first-officially-recorded-instance-of-the-duke-principle\/","title":{"rendered":"The scoop on scoping FRX variables, and the first officially-recorded instance of the Duke Principle"},"content":{"rendered":"

Cesar<\/a>\u00a0responded to my recent walkthrough on barcharting<\/a>\u00a0with some VFPReport-specific questions.\u00a0 Here is his first one:<\/p>\n

At this moment, I’m doing something like this:<\/p>\n

SET REPORTBEHAVIOR 90
\nPRIVATE oFoxChart && needed by report<\/span>
\noxFoxChart = ThisForm.Foxcharts1.ChartCanvas && image control<\/span>
\nREPORT FORM FoxChartsView PREVIEW
\n<\/span>
\nIn my report, in the “ControlSource” I’m passing the “oFoxChart” reference, and it gets printed.<\/p>\n

Is that the best way to do that?<\/p><\/blockquote>\n

In my opinion, probably not.<\/p>\n

It’s really hard to tell, because (as I told Cesar) I don’t have a lot of time to investigate his use of the image control. I don’t really understand why this chart-handling object should be scoped to a form, for example.<\/p>\n

My first question to Cesar was: why aren’t you putting this object in the GFX collection?<\/p>\n

Cesar\u00a0answered, “Oh, sorry, I didn’t get what you meant here.\u00a0 Could you recommend me somewhere to do some researches regarding this?”<\/p>\n

Sure.<\/p>\n

Start with the TMM docoid on FXand GFX Inteface Implementations<\/a>.\u00a0 It takes only one method implementation to become part of the appropriate collection.\u00a0Read the TMM docoid covering the ReportListener Decorator Foundation Class<\/a>, which hosts the FX and GFX collections.\u00a0 Read the Data Visualization in Reports with VFP 9.0 SP2 article<\/a>, in which Colin and I thoroughly worked through a GFX scenario.<\/p>\n

Check out the TMM docoid on GFX Page Region Export<\/a>, while you’re at it.\u00a0 The sample code section\u00a0states that it is an excerpt from code in “a custom graphing object”, which should give Cesar some idea that this approach actually works for what Cesar has in mind.<\/p>\n

In point of fact, the example code in that topic has nothing to do with graphing, it is just illustrating one of two ways for a graphing object to\u00a0interact with and leverage\u00a0an Output Clip (or “Page Region Export”) object, so he might not be interested, but there are other types of synergy between the code for this gfx object and his work, so, hey, check it out.\u00a0 Maybe I’ll use gfxOutputClip to\u00a0illustrate some other ideas in a followup post, in which I’ll try to address some of Cesar’s other questions.<\/p>\n

The\u00a0trouble is, I’m kind of embarrassed to be having to suggest this stuff. It’s not like we hid our recommendations; we first\u00a0published these suggestions in the helpfile that shipped with RTM.\u00a0 In SP2,\u00a0we implemented production-quality examples of our recommendations and shipped them with the product.<\/p>\n

Hence the application of the Duke Principle; more about that below.\u00a0 For now, let’s just get some work done.<\/p>\n

Let’s roll up our sleeves<\/h4>\n

Let’s assume that Cesar has really good reasons to tightly couple his charting object to a form or form class.\u00a0 For example, let’s suppose the data required by the chart isn’t actually available during the run of the FRX, only to the form.<\/p>\n

This problem — how do you scope variables for a report — has more general application than Cesar’s question. That gives me an excuse to explore it in a bit of depth. There are a number of different interesting things to be learned from playing with this question, so, using the image control scenario as context,\u00a0I am going to build up an answer in “layers”.<\/p>\n

The basic principles we’re going to explore include:<\/p>\n