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This chapter is from the book

This chapter is from the book

Writing the Sample Application

Now, you're ready to write your sample application. Begin by creating a project called Chapter3:

MODIFY PROJECT Chapter3

Leave it open because if you close a FoxPro project before you've added anything to it, it asks you if you want to delete the empty project file, and that's just one more thing to deal with.

My MAIN.PRG will create a few settings, put a title on the screen, instantiate my DataTier object, install the menu, and initiate the event loop (see Listing 3.3).

Listing 3.3 MAIN.PRG

* Purpose.....: MAIN program for application

CLEAR ALL
CLOSE ALL
CLEAR
CLOSE ALL
SET TALK    OFF
SET CONFIRM  ON
SET MULTILOCKS ON
SET CENTURY  ON
SET EXCLUSIVE ON
SET SAFETY   OFF
SET DELETED  ON
SET STRICTDATE TO 0

WITH _Screen
.AddObject ( [Title1], [Title], 0, 0 )
.AddObject ( [Title2], [Title], 3, 3 )
.Title2.ForeColor = RGB ( 255, 0, 0 )
ENDWITH

ON ERROR DO ErrTrap WITH LINENO(), PROGRAM(), MESSAGE(), MESSAGE(1)

DO MENU.MPR

oDataTier = NEWOBJECT ( [DataTier], [DataTier.PRG] )
oDataTier.AccessMethod = [DBF]  && Required to execute Assign method code

IF NOT EMPTY ( oDataTier.AccessMethod )
  READ EVENTS
ENDIF

ON ERROR

SET PROCEDURE TO
SET CLASSLIB TO

SET SYSMENU TO DEFAULT

WITH _Screen
.RemoveObject ( [Title1] )
.RemoveObject ( [Title2] )
ENDWITH

DEFINE CLASS Title AS Label
Visible  = .T.
BackStyle = 0
FontName = [Times New Roman]
FontSize = 48
Height  = 100
Width   = 800
Left   = 25
Caption  = [My application]
ForeColor = RGB ( 192, 192, 192 )

PROCEDURE Init
LPARAMETERS nTop, nLeft
THIS.Top = _Screen.Height – 100
IF PCount() > 0
  THIS.Top = THIS.Top - nTop
  THIS.Left= THIS.Left – nLeft
  THIS.ForeColor = RGB(255,0,0)
ENDPROC

ENDDEFINE

PROCEDURE ErrTrap
LPARAMETERS nLine, cProg, cMessage, cMessage1
OnError = ON("Error")
ON ERROR
IF NOT FILE ( [ERRORS.DBF] )
  CREATE TABLE ERRORS (  ;
  Date   Date,     ;
  Time   Char(5),   ;
  LineNum Integer,   ;
  ProgName Char(30),   ;
  Msg   Char(240),  ;
  CodeLine Char(240)   )
ENDIF
IF NOT USED ( [Errors] )
  USE ERRORS IN 0
ENDIF
SELECT Errors
INSERT INTO Errors VALUES ( ;
 DATE(), LEFT(TIME(),5), nLine, cProg, cMessage, cMessage1 )
USE IN Errors
cStr = [Error at line ] + TRANSFORM(nLine) + [ of ] + cprog + [:] + CHR(13)  ;
   + cMessage + CHR(13) + [Code that caused the error:] + CHR(13) + cMessage1
IF MESSAGEBOX( cStr, 292, [Continue] ) <> 6
  SET SYSMENU TO DEFAULT
  IF TYPE ( [_Screen.Title1] ) <> [U]
   _Screen.RemoveObject ( [Title2] )
   _Screen.RemoveObject ( [Title1] )
  ENDIF
  CLOSE ALL
  RELEASE ALL
  CANCEL
 ELSE
  ON ERROR &OnError
ENDIF

Don't try to run it yet because that reference on line 25 to MENU.MPR refers to a menu that we haven't yet created. The menu is where requests to show forms are located, as well as the all-important CLEAR EVENTS command that will end the event loop and allow the program to march onward to its eventual self-destruction.

Next I'll add a menu. I want to be able to switch between DBF and SQL access at will, so that I can verify that my program works exactly the same way with both data stores. So my menu (in which I've already added calls to a couple of screens that we'll build in this chapter) looks like Listing 3.4.

Listing 3.4 Menu.MPR

SET SYSMENU TO
SET SYSMENU AUTOMATIC

DEFINE PAD FilePad    OF _MSYSMENU PROMPT "File"
DEFINE PAD TablePad   OF _MSYSMENU PROMPT "Tables"
DEFINE PAD DataPad    OF _MSYSMENU PROMPT "Change data access"
ON PAD FilePad      OF _MSYSMENU ACTIVATE POPUP file
ON PAD TablePad     OF _MSYSMENU ACTIVATE POPUP tables

ON SELECTION PAD DataPad OF _MSYSMENU DO ChangeAccess IN MENU.MPR

DEFINE POPUP file MARGIN RELATIVE
DEFINE BAR 1 OF file PROMPT "E\<xit"
ON SELECTION BAR 1 OF file CLEAR EVENTS

DEFINE POPUP tables MARGIN RELATIVE SHADOW COLOR SCHEME 4
DEFINE BAR 1 OF tables PROMPT "Customers" SKIP FOR WEXIST([frmCustomer])
DEFINE BAR 2 OF tables PROMPT "Employees" SKIP FOR WEXIST([Employees] )

ON SELECTION BAR 1 OF tables do form frmCustomer
ON SELECTION BAR 2 OF tables do form Employee

PROCEDURE ChangeAccess
oDataTier.AccessMethod = ;
 UPPER(INPUTBOX("Data access method", "DBF/SQL/XML/WC", "DBF" ))

What's oDataTier? That's next. The DataTier controls everything about access to data. So the first thing we do is add a property called AccessMethod, use its Assign method to trap and validate the assignment, and then do whatever needs to be done based on the method chosen. More about that later. Type

BUILD EXE Chapter3 FROM Chapter3

or use the project's Build button. Then use DO Chapter3, or press either the Ctrl+D shortcut key or Alt+P, D to activate the menu and bring up the Do dialog screen and select Chapter3.exe.

Figure 3.1 shows the application's main screen. That third menu selection should look interesting. By the end of this chapter, you'll be able to click on it and try your forms using either data source. The source code is downloadable from the Sams Web site, http://www.samspublishing.com. Also, readers can download this or any other source code from my site, http://www.LesPinter.com.

Figure 3.1Figure 3.1 The main application screen.

We've already done something that would have stopped Visual Basic .NET in its tracks. The DO FormName references to the two forms that don't yet exist would be compiler errors in .NET. As far as FoxPro knows, the forms are right there in the application directory, or somewhere on the path; we simply have our reasons for excluding the forms from the build. Unlike Visual Basic .NET, FoxPro trusts us to come up with the forms by the time we ask for them.

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