The LA Fox Developer Newsletter

October 1997

Automatic Combo Boxes (Cony from page 1)

This gives us a basic dropdown list combo box. Now for the

automation. Add a new property called PopupKey with a value

of NoKeySet. Open up the init event for the combo box and add

the following code:

PRIVATE ISource

ISource

= “SELECT zpuValue FROM;

zPopup WHERE zpuKey = “ +;

ALLT(This.PopupKey) +;

“‘AND !DELETED();

ORDER BY 1 INTO;

Cursor” + ThIs.Name

This.RowSource = lSource

This.Refresh

The above code sets the RecordSource for the combo box to an

SQL statement that retrieves the appropriate values from the

zPopup table. To use the control, simply place it on a form and

set the PopupKey property to the key value in your table. This

would be "Phone" or “Auto” for out example combos. It doesn’t

get much simpler than that!

That takes care of populating the table, let’s let the user control

the values that are in the table. My method is for the user to

right-click the combo box. This opens a form that shows all the

values for that combo box where the user can add, delete, and

edit.

Add a new property to the combo called AllowEdit. Set the

value to .T. by default. Add code to the RightClick event as

follows:

IF This.AllowEdit

Do Form “zfrmPopup” WITH This.PopupKey

This.Requery

=zMsg(”o”, “Edits are not allowed on this popup.”,;

“Edit Not Allowed”, “I”)

Form zfrmPopup has one grid that displays the zpuValues. I

filter the grid based on the key value that is based. Make the

form modal and the combo box will requery itself when you

close the form. I’ll leave the actual code of the form up to you.

That’s all there is to it. You now have a combo box that allows

the user to edit the values in the list and you can effortlessly

add any number of combo boxes to your application.

[Ed. Note: Todd Landrum is an independent developer. His

company, Paladin Programming, writes custom software for

businesses in the Denver area. He is a member of the Rocky

Mountain Foxpro User Group. Todd can be reached at (303)

744-0854 orby e-mail at paladin@ecentral.com.)

Pop-ups with a Temporary

Error Handler

By Andy Neil

FoxPro’s ON ERROR command lets you replace the default

error handler (‘cancel, suspend, ignore’) with your own. This

feature can be a ‘hook’ for fancy error reporting programs. But an

error handler doesn’t need to be a huge user-defined function

(UDF) with a full user interface to be handy. In some cases, you

just want to detect that an error occurred.

For example, let’s say you want to write a procedure that adds

a “Suspend” bar to one of your application’s menu pop-ups. You

also want to run this procedure from a hot key at any time. You

can’t define a bar for a non-existent pop-up, so you’ll need to

check for it first. There’s a problem, though-FoxPro doesn’t have

a function to do that! Without an ISPOPUPO, how do you

confirm that it’s out there? You do it with a temporary error

handler, as illustrated in TMPONERR.PRG:

*

LIsting I

*

TMPONERR.PRG - uses temporary

*

error handler

PRIVATE IcWasOnErr, IlPopupOk, InNewBar

*

Save the old error handler name

lcWasOnErr = ON(’ERROR)

*

Initialize a flag

IIPopupOK = .T.

*

Temporary error handler

ON ERROR IlPopupOK = .F.

*

Where to put new bar?

InNewBar = CNTBAR(’MYPOPUP’) + 1

*

Restore old error handler

ON ERROR &lcWasOnErr

*

Missing popup?

IF !m.IIPopupOK

DEFINE POPUP MYPOPUP FROM 5,5

InNewBar = I

ENDIF

*

MYPOPUP exists, guaranteed!

DEFINE BAR InNewBar OF MYPOPUP;

PROMPT ‘Suspend’

ON SELECTION BAR InNewBar OF MYPOPUP SUSPEND

ACTIVATE POPUP MYPOPUP

RETURN

**EOF TMPONERR.PRG**

At first glance, it looks like the code inside the IF statement

would never be reached since m.IIPopupOK has to be true. The

trick here is in the line with CNTBARO. If ‘MYPOPUP’ hasn’t

been defined, the CNTBARO function will yield an error. If you

were using the default FoxPro error handler, this would put up

the usual dialog box. Instead, when CNTBARO hits the error,

your temporary handler is called.

In this example, the entire “handler” is one statement, which

sets a logical flag to indicate that an error occurred, then returns

control to the executing procedure. The IF statement traps this

and issues the DEFINE POPUP, letting the rest of the code run

successfully. You could wait for the DEFINE BAR statement

itself to trigger the error, but then you’d have to write loops to

(Con’t, page 8)

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