Welcome!

AJAX & REA Authors: Andreas Grabner, Greg O'Connor, Manuel Weiss, Kevin Benedict, RealWire News Distribution

Related Topics: PowerBuilder, .NET

PowerBuilder: Article

The PostOpen Event – Why It Is So Important

PowerBuilder fundamentals

Normally I try to write applications on the DataWindow or Appeon but every now and then I get a question that makes me sit back and say, "Huh?"

In this case the question concerns the PostOpen event. I've seen that event named different things: ue_post_open, postOpen, post_open, ue_postOpen, etc. It has, as far as I can see, always had post and open in the name of the event. Further, just about every framework that I've ever seen has had that event in the base window.

The question that I was asked was, "Why is that event there?"

The programmer wanted to know why there was code in the post open and why was it not just put at the end of the open event? At first I was really confused by the question. It was like he was asking me why do we have arrays? I just couldn't imagine not knowing the answer.

Then it occurred to me that I learned the answer to that question from a book that was published almost 20 years ago. As far as I can tell there are no new books on PowerBuilder and there are only two print magazines, this one and the ISUG magazine.

That's it.

Further I came to think of the tremendous responsibility that the few PowerBuilder authors share. New PowerBuilder programmers turn to us for information and there aren't that many of us left writing. So that leaves a whole lot of PowerBuilder programmers who get all their training from reading the code of other programmers.

Often those other programmers were consultants who wrote the code ten years ago and worked for consulting firms that no longer exist.

To make a bad situation worse a lot of times those programmers are brave souls that have been recruited from other disciplines. When the company finds that their last PowerBuilder programmer has just quit because he got a much better offer they turn to their existing programming staff and ask who would like to pick up PowerBuilder. They may point out that there are 6 or 10 or, as in the case for one company for which I recently worked, 26 PowerBuilder programs that are all critical to the company. The PowerBuilder programmer would become indispensable to the company.

So suddenly a brave Visual Basic or Java programmer finds PowerBuilder installed on his machine. His boss pats him on his pointy little head and tells him that Google is his friend.

Where would you turn? If you picked up the mantle and offered to learn a language that you knew nothing about, what would you do? You'd turn to Amazon or Google. If you type "best PowerBuilder books" in Google the first mentioned is my Definitive DataWindow which was published 13 years ago and is embarrassingly out of date...and out of print.

Let's go to Amazon, there you will find the latest PowerBuilder book is for version 9. It was published 10 years ago. Since then... nothing.

Why should I be surprised that things that I find fundamental are entirely unknown by the newest PowerBuilder programmers.

Warning: If you are a seasoned PowerBuilder programmer the rest of this article will bore you silly.

There is an open event in a window. This is the event that happens when the window is "opened." Now the word ‘open' can be deceptive. A lot of people feel that a window is only opened when it is shown on the screen.

That would be wrong.

The open of a window begins when the open command is issued. That is to say, with a line like:

Open(w_client_editor)

The problem, the whole reason that a post open event is required goes all the way back to Microsoft Windows 3.0 Old Windows programmers will remember version 3.0 very well. Version 3.0 was almost the death of Microsoft Windows. It was unbearably slow. I am not exaggerating; it was the slowest version of Windows that was ever released.

It was so slow that Windows users were seriously studying what the impact of changing to another - any other - operating system would be.

This time Microsoft listened... and panicked. They did a study to determine what it is that makes the user perceive speed in an application. What could be changed to cause the user to believe that the application is faster with minimal real change to the operating system? It wasn't that Microsoft didn't want to address their problems with speed, they most certainly did, but addressing those problems would take time that Microsoft just didn't have. Microsoft was about to lose a lot of customers and once lost, it would be hard to get them back.

Microsoft learned that the visual perception strongly influenced the user's perception of speed. They learned that if the window POPPED onto the screen, all at once, even if the data wasn't there yet, then the users perceived speed. What killed the user perception was when they pressed a button and nothing happened for four seconds. The user would often punch that button two or three times. So Microsoft created operating system queues.

The graphics queue happened before the application queue. So graphics could be given a higher priority than the application and windows would paint faster. They released version 3.1 which was mostly just the addition of these queues (along with other changes like a floating point emulator in assembly code).

This was great but it broke the relationship of the open event with the code. This meant that you weren't guaranteed that everything would be created in the window until after the open event finishes.

Consider this code:

W_customer.open() event
Dw_1.setTransObject(sqlca)
Dw_1.retrieve()

This code would often result in a "Null object reference" error because dw_1 had not been created by Microsoft when the code ran.

Imagine how we felt when this happened. There was a null object reference in line 1 of the open event, but, but, but... that's dw_1. There it is, right there on the window! How can it be null? It's not dynamic. You put it there.

Okay, we learned that we should not put anything in the open event that referred to anything on the screen. Most of us learned to just not put anything at all in the open event except one line in the ancestor:

W_root.open() event
post event ue_post_open( )

For reasons already stated I imagine I can't rely on you knowing the difference between post event and trigger event or for that matter between postOpen and post open.

Okay, one at a time. Posting an event means that Microsoft Windows will open this window after the rest of the code in this script is executed. Basically it means, "Do this when you get a chance." So if you add that to the open event of your root window then it will call the ue_post_open event after all of the code in all of the descendants of this window is done.

Keep in mind the order of execution of events. First PowerBuilder goes to the farthest ancestor and then starts executing down the inheritance tree. If you have w_grandpa, and w_pa inherits from that and w_son inherits from that then the code in w_grandpa.open would execute first, then the code in w_pa, finally the code in w_son.

This means that if we put the post event in the open of w_grandpa, then the ue_post_open would happen after the last open event in the descendants. In our example:

W_grandpa.open->w_pa.open->w_son.open-> w_grandpa.ue_post_open-> w_son.ue_post_open->w_son.post_open

All that we have to do is create a ue_post_open event in our root window. We don't have to put anything in it, just create one. Then we post that event from the open event and we have a place now to put all our initialization code and don't have to worry about whether any object exists or not.

More important the screen will quickly draw or paint, giving the user the perception of speed. If you need to retrieve data and know it will take a short time, then you can set the pointer to an hourglass. I guarantee that your user will feel the window is faster.

I mentioned that most of us learned not to put anything in the open event. There is an exception to that rule. When your window is opened with a parameter then you should access the message object as the first line of code in your window.

Let me give you an example. Suppose that you open a window with a customer_id. You are going to use that customer_id as a parameter to the datawindow dw_1. Here is what you would do.

W_calling_window
Long ll_customer_id
Ll_customer_id = dw_detail.getItemNumber(dw_detail.getRow(), "customer_id")
openWithParm(w_customer_detail, ll_customer_id)

Now in the w_customer_detail window you need to set an instance variable. That's because we have just passed a variable to the new window and we are going to get it in the open event but we are going to retrieve the DataWindow in the ue_postOpen event. So let's do this. I will assume that you know how to declare an instance variable. Let's name it il_customer_id. Now let's look at the open event of w_customer_detail.

W_customer_detail.open()
il_customer_detail = message.longParm

Okay, now in the open event of w_customer_detail we have taken the longParm property of the global message object and put it in an instance variable.

Since we have inherited the w_customer_detail from whatever our base window is, the ue_postOpen event will automatically fire. That means that we don't have to fire off the event. Now I just have to put the code that we need in the window.

W_customer_detail.ue_postOpen()
dw_customer_info.setTransObject(sqlca)
dw_customer.retrieve(il_customer_detail)

Let's Do Some Housekeeping
I think that we've pretty well covered the post open event but in the process of doing that I've brought up a couple of other issues that I'd like to cover just to be complete.

First let's talk about post event as opposed to postEvent.

With the post event command you must know the name of the event that you want to post. You can pass the parameters normally. However, just like calling a function, the event has to exist and the parameters must be correct.

On the other hand the postEvent function takes a string as a parameter and that string is the name of the event. This means that you can store the name of the event in a table. In fact the event doesn't even have to exist. If it doesn't then nothing will happen. There will be no error thrown.

This makes the postEvent perfect for security systems where you can post an event based on a security role. Here is some code that might work for you in a menu event.

M_main.m_file.m_save.clicked
Datastore ld_security, ld_events
ld _secutity = create datastore
ld_events = create datastore

ld_events.dataobject = "d_events"
ld_security.dataobject = "d_get_security"

ld_events.setTransObject(sqlca)
ld_security.setTransObject(sqlca)

parentWindow.postEvent(ld_events.retrieve(ld_security.retrieve(gs_user_id)))

Using the postOpen function is very flexible but it is limited in the parameters that can be passed it. If you use the post event command, you can pass any number of parameters that you wish. The caveat is that the event must exist or you will get a compile time error. So the event that you used before for security cannot be done.

All that I just said for the postEvent and post event command applies also to the triggerEvent and trigger event commands.

Finally I'd like to mention the global message object.

This object is global. It can be accessed at any time by any other object. That means that if you access the message object in the postOpen event then another window may have changed your message object properties and this could corrupt what you are expecting.

Don't take this lightly. More than once I've debugged and found this error and believe me it is difficult to find. The problem is that it is not an error with logic or data but a timing error. These can be close to impossible to find.

Please take my word for this, make it a golden rule. If you open a window with a parameter, the first thing you do in the target or opened window is grab that value from the message object and store it.

Also, if you do a closeWithReturn then you need to immediately get the value from the message object.

There you have it. I've covered in some detail some basic information that might not be so easily learned any more.

More Stories By Richard (Rik) Brooks

Rik Brooks has been programming in PowerBuilder since the final beta release before version 1. He has authored or co-authored five books on PowerBuilder including “The Definitive DataWindow”. Currently he lives in Mississippi and works in Memphis, Tennessee.

Comments (1) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
ywerde 02/20/13 04:14:00 PM EST

In your introduction you clearly state the problem new PowerBuilder developers face when they find the IDE installed on their machine. You then go on to talk about the lack of current training materials.
One important cost effective training resource you omitted is the online training from ISUG/eLearnIT. Everyone can learn more here.

Cloud Expo Breaking News
Simply defined the SDDC promises that you’ll be able to treat “all” of your IT infrastructure as if it’s completely malleable. That there are no restrictions to how you can use and assign everything from border controls to VM size as long as you stay within the technical capabilities of the devices. The promise is great, but the reality is still a dream for the majority of enterprises. In his session at 14th Cloud Expo, Mark Thiele, EVP, Data Center Tech, at SUPERNAP, will cover where and how a business might benefit from SDDC and also why they should or shouldn’t attempt to adopt today.
MapDB is an Apache-licensed open source database specifically designed for Java developers. The library uses the standard Java Collections API, making it totally natural for Java developers to use and adopt, while scaling database size from GBs to TBs. MapDB is very fast and supports an agile approach to data, allowing developers to construct flexible schemas to exactly match application needs and tune performance, durability and caching for specific requirements.
APIs came about to help companies create and manage their digital ecosystem, enabling them not only to reach more customers through more devices, but also create a large supporting ecosystem of developers and partners. While Facebook, Twitter and Netflix were the early adopters of APIs, large enterprises have been quick to embrace the concept of APIs and have been leveraging APIs as a connective tissue that powers all interactions between their customers, partners and employees. As enterprises embrace APIs, some very specific Enterprise API Adoption patterns and best practices have started emerging. In his session at 14th Cloud Expo, Sachin Agarwal, VP of Product Marketing and Strategy at SOA Software, will talk about the most common enterprise API patterns and will discuss how enterprises can successfully launch an API program.
The social media expansion has shown just how people are eager to share their experiences with the rest of the world. Cloud technology is the perfect platform to satisfy this need given its great flexibility and readiness. At Cynny, we aim to revolutionize how people share and organize their digital life through a brand new cloud service, starting from infrastructure to the users’ interface. A revolution that began from inventing and designing our very own infrastructure: we have created the first server network powered solely by ARM CPU. The microservers have “organism-like” features, differentiating them from any of the current technologies. Benefits include low consumption of energy, making Cynny the ecologically friendly alternative for storage as well as cheaper infrastructure, lower running costs, etc.
Next-Gen Cloud. Whatever you call it, there’s a higher calling for cloud computing that requires providers to change their spots and move from a commodity mindset to a premium one. Businesses can no longer maintain the status quo that today’s service providers offer. Yes, the continuity, speed, mobility, data access and connectivity are staples of the cloud and always will be. But cloud providers that plan to not only exist tomorrow – but to lead – know that security must be the top priority for the cloud and are delivering it now. In his session at 14th Cloud Expo, Kurt Hagerman, Chief Information Security Officer at FireHost, will detail why and how you can have both infrastructure performance and enterprise-grade security – and what tomorrow's cloud provider will look like.
Today, developers and business units are leading the charge to cloud computing. The primary driver: faster access to computing resources by using the cloud's automated infrastructure provisioning. However, fast access to infrastructure exposes the next friction point: creating, delivering, and operating applications much faster. In his session at 14th Cloud Expo, Bernard Golden, VP of Strategy at ActiveState, will discuss why solving the next friction point is critical for true cloud computing success and how developers and business units can leverage service catalogs, frameworks, and DevOps to achieve the true goal of IT: delivering increased business value through applications.
Web conferencing in a public cloud has the same risks as any other cloud service. If you have ever had concerns over the types of data being shared in your employees’ web conferences, such as IP, financials or customer data, then it’s time to look at web conferencing in a private cloud. In her session at 14th Cloud Expo, Courtney Behrens, Senior Marketing Manager at Brother International, will discuss how issues that had previously been out of your control, like performance, advanced administration and compliance, can now be put back behind your firewall.
More and more enterprises today are doing business by opening up their data and applications through APIs. Though forward-thinking and strategic, exposing APIs also increases the surface area for potential attack by hackers. To benefit from APIs while staying secure, enterprises and security architects need to continue to develop a deep understanding about API security and how it differs from traditional web application security or mobile application security. In his session at 14th Cloud Expo, Sachin Agarwal, VP of Product Marketing and Strategy at SOA Software, will walk you through the various aspects of how an API could be potentially exploited. He will discuss the necessary best practices to secure your data and enterprise applications while continue continuing to support your business’s digital initiatives.
The revolution that happened in the server universe over the past 15 years has resulted in an eco-system that is more open, more democratically innovative and produced better results in technically challenging dimensions like scale. The underpinnings of the revolution were common hardware, standards based APIs (ex. POSIX) and a strict adherence to layering and isolation between applications, daemons and kernel drivers/modules which allowed multiple types of development happen in parallel without hindering others. Put simply, today's server model is built on a consistent x86 platform with few surprises in its core components. A kernel abstracts away the platform, so that applications and daemons are decoupled from the hardware. In contrast, networking equipment is still stuck in the mainframe era. Today, networking equipment is a single appliance, including hardware, OS, applications and user interface come as a monolithic entity from a single vendor. Switching between different vendor'...
Cloud backup and recovery services are critical to safeguarding an organization’s data and ensuring business continuity when technical failures and outages occur. With so many choices, how do you find the right provider for your specific needs? In his session at 14th Cloud Expo, Daniel Jacobson, Technology Manager at BUMI, will outline the key factors including backup configurations, proactive monitoring, data restoration, disaster recovery drills, security, compliance and data center resources. Aside from the technical considerations, the secret sauce in identifying the best vendor is the level of focus, expertise and specialization of their engineering team and support group, and how they monitor your day-to-day backups, provide recommendations, and guide you through restores when necessary.
Cloud scalability and performance should be at the heart of every successful Internet venture. The infrastructure needs to be resilient, flexible, and fast – it’s best not to get caught thinking about architecture until the middle of an emergency, when it's too late. In his interactive, no-holds-barred session at 14th Cloud Expo, Phil Jackson, Development Community Advocate for SoftLayer, will dive into how to design and build-out the right cloud infrastructure.
You use an agile process; your goal is to make your organization more agile. What about your data infrastructure? The truth is, today’s databases are anything but agile – they are effectively static repositories that are cumbersome to work with, difficult to change, and cannot keep pace with application demands. Performance suffers as a result, and it takes far longer than it should to deliver on new features and capabilities needed to make your organization competitive. As your application and business needs change, data repositories and structures get outmoded rapidly, resulting in increased work for application developers and slow performance for end users. Further, as data sizes grow into the Big Data realm, this problem is exacerbated and becomes even more difficult to address. A seemingly simple schema change can take hours (or more) to perform, and as requirements evolve the disconnect between existing data structures and actual needs diverge.
SYS-CON Events announced today that SherWeb, a long-time leading provider of cloud services and Microsoft's 2013 World Hosting Partner of the Year, will exhibit at SYS-CON's 14th International Cloud Expo®, which will take place on June 10–12, 2014, at the Javits Center in New York City, New York. A worldwide hosted services leader ranking in the prestigious North American Deloitte Technology Fast 500TM, and Microsoft's 2013 World Hosting Partner of the Year, SherWeb provides competitive cloud solutions to businesses and partners around the world. Founded in 1998, SherWeb is a privately owned company headquartered in Quebec, Canada. Its service portfolio includes Microsoft Exchange, SharePoint, Lync, Dynamics CRM and more.
The world of cloud and application development is not just for the hardened developer these days. In their session at 14th Cloud Expo, Phil Jackson, Development Community Advocate for SoftLayer, and Harold Hannon, Sr. Software Architect at SoftLayer, will pull back the curtain of the architecture of a fun demo application purpose-built for the cloud. They will focus on demonstrating how they leveraged compute, storage, messaging, and other cloud elements hosted at SoftLayer to lower the effort and difficulty of putting together a useful application. This will be an active demonstration and review of simple command-line tools and resources, so don’t be afraid if you are not a seasoned developer.
SYS-CON Events announced today that BUMI, a premium managed service provider specializing in data backup and recovery, will exhibit at SYS-CON's 14th International Cloud Expo®, which will take place on June 10–12, 2014, at the Javits Center in New York City, New York. Manhattan-based BUMI (Backup My Info!) is a premium managed service provider specializing in data backup and recovery. Founded in 2002, the company’s Here, There and Everywhere data backup and recovery solutions are utilized by more than 500 businesses. BUMI clients include professional service organizations such as banking, financial, insurance, accounting, hedge funds and law firms. The company is known for its relentless passion for customer service and support, and has won numerous awards, including Customer Service Provider of the Year and 10 Best Companies to Work For.