10 PowerBuilder Pitfalls

First the good news: PowerBuilder is a great tool; in fact you can't
accidentally do much wrong. This
strength is based on a number of reasons. The following is list of why
I think PowerBuilder is so great, but
you might like to add one or two more items to it:
PowerScript is simple; it's easy to learn because of its clearly
laid out grammar.
PowerScript is a strongly typed language; many problems
simply don't arise because of the compiler telling you about an
error.
PowerScript is easy to read. PowerBuilder itself takes care of
the tedious task of correct indentation. Thus PowerBuilder
programs look pretty much the same in terms of "layout" in all
PowerBuilder shops around the world.
There is no pointer system. You cannot access addresses of objects and
do nasty things with them.
PowerBuilder does all the low-level memory management for you. There's
no need to allocate and
dealloacate memory for strings or arrays, as it's done for you. When
using objects, garbage collection
cleans up after you.
No dangling pointers. All references to a single object become invalid
whenever the the object is
destroyed and can be checked by using IsValid().
Values of simple data types are initialized - numeric values with
zero, Booleans with FALSE, etc.
Those elements are part of the strength of PowerBuilder (plus the
DataWindow, of course). However, there
are a few pitfalls in PowerBuilder programming that seem to frequently
occur. This article will show you
some of those issues. I have collected them over time in my function
as technical lead where I do a lot of
code review and "programmers first-level support" as I repeatedly come
across the same problems. For
some of the problems, I'll propose a workaround to make your programs
safer. Let's start.
1. Find With Wrong Parameters
What's wrong with the following piece of code?
l_max = ds.RowCount()
l_index = ds.Find('x>5', 1, l_max)
DO WHILE l_index > 0
of_WorkOn(l_index)
l_index = ds.Find('x>5', l_index + 1, l_max)
LOOP
Answer: It hides a potential endless loop - Find() can search
backwards! If the value in column x is greater
than 5 in the last row of the DataStore, l_index will eventually
become l_max. The Find() will read:
l_index = ds.Find('x>5', l_max + 1, l_max)
PowerBuilder recognizes that l_max + 1 is greater than l_max and will
start to search backwards. Of course,
it will find the row l_max that fits the expression. The perfect
endless loop is done.
HOW TO AVOID PITFALL 1:
This behavior is documented and thus won't change. What can we do
about it? There are two workarounds:
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Always code the Find finishing not at RowCount(), but at RowCount() + 1.
Implement a function Find in your DataWindow or DataStore ancestor
class that only takes two
arguments: the expression and the starting row. Within the function
use the solution stated above.
2. Incorrect Boolean DataWindow Expressions
This pitfall is really a major problem if programmers are not aware of
it, so be warned. PowerBuilder
supports two language grammars: PowerScript and DataWindow Expression
syntax. Many functions known
from PowerScript are available within DataWindow expressions as well,
so it's easy for us to code in each
of them. But beware, there are some subtle and very important differences.
Whats's wrong with the following expression?
NOT IsNull(x) AND x > 100
Nothing really. At least if you use it within PowerScript, PowerScript
will evaluate it to
(NOT IsNull(x)) AND (x > 100)
But take care: if you use the same expression within a DataWindow (for
Find, Filter, etc.), PowerBuilder
will evaluate it to:
NOT (IsNull(x) AND (x > 100))
therefore evaluating it to FALSE, because a value cannot be NULL and
greater than 100 at the same time.
What is the reason for that?
DataWindow expressions have a different operator precedence for
logical operators compared to
PowerScript (and just about any other computer language I know).
Usually NOT has precedence over AND,
and AND has precedence over OR. But within DataWindow expressions, AND
and OR have precedence
over NOT. AND and OR will be evaluated in the order of how they occur.
This is very weird, but still is expected and documented behavior.
Simply start PowerBuilder help and
search for "operators:precedence", and you'll find the two diverging
styles of logical operator precedence
within PowerBuilder.
HOW TO AVOID PITFILL 2:
The only way you can get around this problem is to use brackets to
tell PB explicitly what you mean. For
the example above you'll need to write:
(NOT IsNull(x)) AND (x > 100)
3.Missing Message Boxes
Sometimes we use MessageBoxes for "quick and dirty" debugging. Once in
a while a programmer tells me
that PowerBuilder is not showing message boxes anymore. Take a look at
the next code snippet; what could
be wrong here?
s_data = ds.GetItemString(1, 'data')
MessageBox('data is', s_data)
The reason that PowerBuilder doesn't show the MessageBox is simple:
s_data is null! And PowerBuilder
does with MessageBox just about the same thing it does with all other
functions that are being called with
nulls as arguments: it does not execute the function but returns null.
HOW TO AVOID PITFALL 3:
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The workaround for that is simple, but involves some work on your
side: you need to code your own
version of function MessageBox (for instance as a global function).
You can't override PowerBuilder
built-in functions without losing the ability to call them, so you
need to give the function a new name, say
MsgBox. The problem is that there is a wealth of overloaded versions
of MessageBox functions, so you
need to implement quite a few. Within each of the calls, check the
arguments for nulls.
4. Not Fully Regenerated Source Code
Sometimes people in the Sybase newsgroups complain that PowerBuilder
is slow and not stable. More often
than not, the reason for that is the source code is not thoroughly
regenerated. This has been especially true
for the early versions of PB 7, where a change within the source of a
function changed the order of the
function list in the source code, which in turn led to incorrect
functions being called if you did not
regenerate all depending (i.e., calling) classes.
HOW TO AVOID PITFALL 4:
The workaround for this is simple: let computers do the dirty work for
you. Do a nightly regeneration of
your sources either with OrcaScript or any of the third-party tools
that focus on that kind of task.
5. Passing Objects per Reference
This is not really a pitfall but rather an aesthetic issue: many
developers apparently still believe that they
need to pass objects "by reference" in order to be able to change
their instance variables. This is wrong,
PowerBuilder does not pass the object but only the object reference
per reference. The only time you'll need
this is when you change the object reference in the called function
(for example, because you create or
re-create it).
HOW TO AVOID PITFALL 5:
That's an easy one: simply use pass by value for objects.
6. New DataWindow Columns Are Not Updatable by Default
A PowerBuilder classic - I guess just about every programmer tripped
over this behavior at least once in his
or her career. Whenever you add a column to a table, you need to add
it to the DataWindow result set in
order to retrieve it from the database. That's the simple part. But,
the newly added columns are not
updatable by default. PowerBuilder used to give those columns a tab
order of 0, so you couldn't edit the
column. However, with more recent builds, newly added columns get the
highest tab order, so you are able
to edit the columns right away. The bad part: those columns won't be
saved until you manually add them to
the list using the "update properties" dialog.
HOW TO AVOID PITFALL 6:
Always remember to edit the update properties when you add a column.
7. Using ClipBoard in a DataWindow
Is the function ClipBoard not working for you? It might be because you
use it within a DataWindow.
Sometimes the clipboard is used to store interim values. Using
ClipBoard(s_data) within DataWindow
source code is not successful, because the function ClipBoard is
implemented within the class DataWindow
with different semantics and thus hides the global function ClipBoard.
The result is that the data you want to
put in the clipboard simply isn't there.
HOW TO AVOID PITFALL 7:
When trying to access the clipboard in DataWindow sources, explicitly
use the global operator :: and
Page 4
therefore write ::ClipBoard(s_data).
8. SetItemStatus Needs Intermediate Step
This is also a PowerBuilder classic but is already well known: there
are some item statuses that can't be set
directly; you need a second SetItemStatus to achieve the goal. One
example: changing the column status
from "new" to "notModified" simply doesn't work. You need to set it to
"dataModified" first, then you can
change it to "notModified". Some others settings are allowed, but
don't work as expected; changing from
"newModified" to "notModified" will change the state to '"new".
HOW TO AVOID PITFALL 8:
Whenever you implement SetItemStatus, check with the PB online help
for the "SetItemStatus method" if
the combination is to be successful. Do an intermediate step if necessary.
9. No Runtime Error for Incorrect SetItems or SetFilters
If you issue an incorrect GetItemX on a DataWindow, PowerBuilder will
raise an error if you used a wrong
row, a wrong column name, or a wrong data type for the column.
Unfortunately, there will be no runtime
errors for incorrect SetItem commands. You need to check the return
code of the function yourself. The
same holds true for SetFilter. I believe these two functions to be
some of the most important ones for PB
scripts as they can influence the flow of execution and the stored data.
HOW TO AVOID PITFALL 9:
In your ancestor classes for DataStore and DataWindow, override all
SetItems and SetFilters and raise an
exception if there is an error. You will make your programs much more robust.
10. No Data After Retrieve
Retrieving data in a datastore doesn't always mean that you have the
read rows available in the primary
buffer. While any experienced PowerBuilder programmer will know this,
it is a common source of
problems for newbies. PowerBuilder applies the filter expression
defined in the DataWindow painter after it
has read the data. So it may happen that you read loads of data and
the return value of Retrieve is zero! Why
is that? The answer is simple: the return value of Retrieve is the
number of rows in the primary buffer after
the Retrieve, not the number of rows retrieved. The two numbers (rows
retrieved versus rows in primary
buffer) might be different in two cases:
There is a filter expression defined that filters some data.
PowerBuilder applies the filter after having
read the rows. You will find those rows in the filter buffer of your
DataWindow/Datastore.
1.
You returned 2 in RetrieveStart, thus not emptying the buffers before
the read. If there had been rows
before the Retrieve, the return value of Retrieve will be the sum of
existing rows and newly read
rows.
2.
HOW TO AVOID PITFALL 10:
Just be aware of the fact. You might want to remove the built-in
filter and do a SetFilter() and Filter in
source code (which is much more readable anyway).
Summary
PowerBuilder has only a few gotchas you need to know in order to write
reliable software. The 10 pitfalls
mentioned above are my personal list of items to be aware of. Keeping
those in mind when programming or
- even better - taking care of them in your base classes will help you
write a robust application.
Do you know of any other issues I didn't mention here? Please drop me
a brief note - if I get enough
Page 5
feedback, I'll compile those issues into another PBDJ article.
www.romu.com

Combining PowerBuilder Help Files

Combining PowerBuilder Help Files

Wouldn't it be nice if all of the help files were combined so you
could hit Shift-F1 on a PB, PFC, or Corporate Extension function and
have it automatically come up?



Well now you can! Just do the following:

* Open pbhlpxx.cnt in Notepad (or any other text editor) and add
the following lines immediately after :Title PowerBuilder Help (the
second line):
:Index PFC Help=pbpfcxx.hlp
:Index Corporate Extension Help=CorpExtn.hlp
:Link pbpfcxx.hlp
:Link CorpExtn.hlp
:Include pbpfcxx.cnt
:Include CorpExtn.cnt
* Save and close the file
* Make sure all of the *.hlp files you have included reside in the
Help folder of your PowerBuilder installation

Using Windows Server 2008 as a SUPER workstation OS

Windows Server 2008 is the best OS to be released till date from Microsoft's stable. And the moment I got hold of the RTM build I could not resist installing it on my workstation. Due to the nature of my work I always prefer running a Server OS on my main workstation... I have been running Windows 2003 disguised as XP (with all the themes and stuff) all these days.

So here is my tale of how I went about setting up Windows Server 2008 to look and fell like its desktop counterpart Windows Vista.

1. Enable Hardware Virtualization

My workstation is a x64 machine with hardware virtualization capabilities. This means I can run Hyper-V on my machine. Even if your machine's hardware supports virtualization it is most likely not going to be enabled by default. You have to enable it via your BIOS setup.

2. Install the latest Graphics and Audio drivers

Being a server OS Windows 2008 carries with it basic graphics and audio drivers. To utilize the full strength of your hardware ensure you install the latest drivers for both graphics and audio hardware. Only with the proper graphics drivers will you be able to enable the "Aero" experience on Windows 2008.

3. Desktop Experience Feature

The Desktop Experience Feature enables a bunch of stuff that is by default present on a desktop OS. Most importantly it includes Themes, Windows Media player and the Aero related features. You will have to enable it form the Server Manager. The "Turn Windows features on or off" / "Add remove windows components" has all been rolled into the Server Manager now.

Server Manager > Features > Desktop Experience

Installing the Desktop Experience feature does not enable them. You have to manually set them up.

4. Themes

To enable Themes you will basically have to enable the Themes Service. Again being a server OS it is not enabled by default.

Services.MSC > Themes

Set the start up type to Automatic

Enabling the Aero Theme.

For this go to Control Panel > Personalization >Theme and select Windows Aero

5. Search

Search is also disabled by default on Windows 2008. Searching is important for me as I use it a lot to find my emails. To enable search you will have to add the File Services Role via Server Manager.

Server Manager > Roles > File Services > Windows Search

Outlook relies on this search service.

6. Disable Shutdown Event Tracker

Since I am using it as a workstation I do not want to keep a track of all the Shutdowns. The Shutdown Event Tracker is the pop up that you get asking you for a shutdown reason. To disable it

Open mmc.msc

Add the Group Policy snap-in

Under Administrative Templates expand System

Set Display Shutdown Event Tracer to Disabled

7. Audio

For audio you need to enable the Windows Audio service. You do this by setting the startup type to Automatic.

Services.msc > Windows Audio

Ensure you have proper drivers for your audio hardware... for me the default driver was not enabling the headphones ... it started working fine after I got the proper driver.

8. SuperFetch

As a workstation, enabling SupertFetch will give you that additional bit of responsiveness. The SuperFetch services is disabled by default and when you try to enable it you will most likely get an error message "The operating system is not presently configured to run this application"

You will have to make two registry changes to enable this service. I basically copied them over from my Vista machine.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters

EnablePrefetcher DWORD 3

EnableSuperfetch DWORD 3

9. Get a codec pack.

For media hungry buffs download a codec pack. This will ensure you can play all media files.

10. Enable Hyper-V

With Hyper-V you can run virtual machines on your workstation. This is useful if you want to run your tests on older OS versions. Enabling Hyper-V is easy

Server Manager > Roles > Hyper-V

Remember you need a Hyper-V enabled Windows 2008 licence and also your hardware has to support virtualization.

Also If you are using an existing VHD it may ask you to re-Activate Windows as it detected hardware changes.

One good thing about Windows Server 2008 is that it no longer asks for the i386 folder like Windows 2003 while you enable features.

Using Windows Server 2008 as a SUPER workstation OS ... Cont'd

Here are a couple of things I missed in my previous post

11. Processor Scheduling

As pointed out in a comment on my previous post; On Windows Server 2008 background services are given preference over interactive programs. You can change this behavior by

Control Panel > System and Maintenance > System > Advanced System Settings > Advanced > Performance > Settings > Advanced > Processor Scheduling

Setting this to Programs will make foreground programs more responsive.

12. Visual Effects

One thing you will notice on Windows Server 2008 is that by default you will not see Preview Thumbnails in your Documents / Music / Video folders. This has to be enabled explicitly.

Control Panel > System and Maintenance > System > Advanced System Settings > Advanced > Performance > Settings > Visual Effects

Based on your preference you can tweak these settings.

13. Power Options

Do your bit for a Green World! The Balanced (default) power plan on Windows Server 2008 does not turn off hard disks by default. On Vista hard disks are turned off after 20 mins. You can change this by

Control Panel > Hardware and Sound > Power Options > Change plan settings

It does take a bit to kick start the hard disks when you resume work but that's a sacrifice worth making for a greener world :).

14. IE Enhanced Security

IE Enhanced Security Configuration has been moved from Add Remove Windows Components (on Windows 2003) to the Server Manager on Windows Server 2008.

Server Manager > Security Information > Configure IE ESC

You now have a choice to disable it only for Administrators.

And to end with a couple of clarifications

* Why am I recommending Windows Server 2008 over Windows Vista ?

I am not!

* How to get Sidebar / Media center on Windows Server 2008?

My honest opinion would be to look for alternatives.

* Will hardware problems go away moving to Windows Server 2008?

Not likely. One of the biggest complaints against Vista was hardware issues. Without proper drivers from your hardware vendors your ride on Windows Server 2008 is again going to be bumpy. For me all Vista compatible drivers worked fine with Server 2008 and I believe they should work for you as well.

* Will all software work on Windows Server 2008?

Most will but some setups detect Windows Server 2008 as a server OS and may not install. The compatibility mode does not have a Vista option only XP / Windows 2003 and other legacy OS.

C# class initialization order

1) Derived static constructor
2) Derived Instance members constructor
3) Base static constructor
4) Base Instance consctructor (members too)
5) Derived Instance constructor