In a previous post, I discussed how an XP is in three distinct parts. This post is about the second part: Where the rubber meets the road.
Because this is the main part of the XP, describing this section in any detail would be like trying to describing how any a website works by describing how HTML works.
But, there are two main functions of every XP. Input and Communicating with the user.
Input: Feeding data from you map into your XP is a major function. If you cannot select elements or locations (points), you cannot have much of an impact on your drawing.
Communication: Having the ability to select something without telling the user what your command is expecting the user to do.
These two functions are accomplished using RDATA (Request Data) and FORMST (Format String). Using these two together, we can prompt the user, with FORMST, that we currently want a type of data (a string, a point, an element etc.) and with RDATA, we are informing CC3 that it needs to let the user collect the data we want.
Here is a simple example that implements an XP command to enter a text word:
Line 1: This is the prototype for the method that RDATA will call when it has gotten a hold of the data you requested.
Line 3: This is the FORMST declaration. This declaration creates a variable (lpszGetText) and assigns it the text "Enter Text:". True, we could have created a string with this text, but RDATA is expecting a FORMST variable. Plus, when we get further into the power of FORMST, you will see that is it not merely a replacement for a char array.
Lines 5 & 6: This is the RDATA declaration. When you learn to read it, you will see that it says it is going to go get a "Word" (a string of characters without whitespace), store it in the char array Text (not declared in the code snippet), diplaying no visible cursor, displaying the text in the FORMST as our prompt and calling our method, GotText, when the user is done entering the request.
Line 8 - 11: This is our commands original method. It would have been declared and prototyped in Part 1 of the XP code.
Line 10: This is the call that invokes our RDATA.
Line 13 - 22: This is our method that RDATA will call when it has gotten a hold of the data you requested.
Line 15: This line shows that the Result parameter contains the "Status" of the request we made. If it is "OK" then we can further process what we got.
Line 20: CmdEnd() is the XP command that notifies CC3 that our XP function has come to an end.