Welcome!

Microservices Expo Authors: Pat Romanski, Gopala Krishna Behara, Sridhar Chalasani, Tirumala Khandrika, Don MacVittie

Related Topics: PowerBuilder, Microsoft Cloud

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.

@MicroservicesExpo Stories
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...
The goal of Microservices is to improve software delivery speed and increase system safety as scale increases. Microservices being modular these are faster to change and enables an evolutionary architecture where systems can change, as the business needs change. Microservices can scale elastically and by being service oriented can enable APIs natively. Microservices also reduce implementation and release cycle time and enables continuous delivery. This paper provides a logical overview of the Mi...
Our work, both with clients and with tools, has lead us to wonder how it is that organizations are handling compliance issues in the cloud. The big cloud vendors offer compliance for their infrastructure, but the shared responsibility model requires that you take certain steps to meet compliance requirements. Which lead us to start poking around a little more. We wanted to get a picture of what was available, and how it was being used. There is a lot of fluidity in this space, as in all things c...
The notion of improving operational efficiency is conspicuously absent from the healthcare debate - neither Obamacare nor the newly proposed GOP plan discusses the impact that a step-function improvement in efficiency could have on access to healthcare (through more capacity), quality of healthcare services (through reduced wait times for patients) or cost (through better utilization of scarce, expensive assets).
Some people are directors, managers, and administrators. Others are disrupters. Eddie Webb (@edwardawebb) is an IT Disrupter for Software Development Platforms at Liberty Mutual and was a presenter at the 2016 All Day DevOps conference. His talk, Organically DevOps: Building Quality and Security into the Software Supply Chain at Liberty Mutual, looked at Liberty Mutual's transformation to Continuous Integration, Continuous Delivery, and DevOps. For a large, heavily regulated industry, this task ...
Modern software design has fundamentally changed how we manage applications, causing many to turn to containers as the new virtual machine for resource management. As container adoption grows beyond stateless applications to stateful workloads, the need for persistent storage is foundational - something customers routinely cite as a top pain point. In his session at @DevOpsSummit at 21st Cloud Expo, Bill Borsari, Head of Systems Engineering at Datera, explored how organizations can reap the bene...
The past few years have seen a huge increase in the amount of critical IT services that companies outsource to SaaS/IaaS/PaaS providers, be it security, storage, monitoring, or operations. Of course, along with any outsourcing to a service provider comes a Service Level Agreement (SLA) to ensure that the vendor is held financially responsible for any lapses in their service which affect the customer’s end users, and ultimately, their bottom line. SLAs can be very tricky to manage for a number ...
"I focus on what we are calling CAST Highlight, which is our SaaS application portfolio analysis tool. It is an extremely lightweight tool that can integrate with pretty much any build process right now," explained Andrew Siegmund, Application Migration Specialist for CAST, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
As many know, the first generation of Cloud Management Platform (CMP) solutions were designed for managing virtual infrastructure (IaaS) and traditional applications. But that's no longer enough to satisfy evolving and complex business requirements. In his session at 21st Cloud Expo, Scott Davis, Embotics CTO, explored how next-generation CMPs ensure organizations can manage cloud-native and microservice-based application architectures, while also facilitating agile DevOps methodology. He expla...
DevOps promotes continuous improvement through a culture of collaboration. But in real terms, how do you: Integrate activities across diverse teams and services? Make objective decisions with system-wide visibility? Use feedback loops to enable learning and improvement? With technology insights and real-world examples, in his general session at @DevOpsSummit, at 21st Cloud Expo, Andi Mann, Chief Technology Advocate at Splunk, explored how leading organizations use data-driven DevOps to close th...
Gaining visibility in today’s sprawling cloud infrastructure is complex and laborious, involving drilling down into tools offered by various cloud services providers. Enterprise IT organizations need smarter and effective tools at their disposal in order to address this pertinent problem. Gaining a 360 - degree view of the cloud costs requires collection and analysis of the cost data across all cloud infrastructures used inside an enterprise.
Admiral Calcote - also known as Lee Calcote (@lcalcote) or the Ginger Geek to his friends - gave a presentation entitled Characterizing and Contrasting Container Orchestrators at the 2016 All Day DevOps conference. Okay, he isn't really an admiral - nor does anyone call him that - but he used the title admiral to describe what container orchestrators do, relating it to an admiral directing a fleet of container ships. You could also say that they are like the conductor of an orchestra, directing...
The past few years have brought a sea change in the way applications are architected, developed, and consumed—increasing both the complexity of testing and the business impact of software failures. How can software testing professionals keep pace with modern application delivery, given the trends that impact both architectures (cloud, microservices, and APIs) and processes (DevOps, agile, and continuous delivery)? This is where continuous testing comes in. D
"WineSOFT is a software company making proxy server software, which is widely used in the telecommunication industry or the content delivery networks or e-commerce," explained Jonathan Ahn, COO of WineSOFT, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
There is a huge demand for responsive, real-time mobile and web experiences, but current architectural patterns do not easily accommodate applications that respond to events in real time. Common solutions using message queues or HTTP long-polling quickly lead to resiliency, scalability and development velocity challenges. In his session at 21st Cloud Expo, Ryland Degnan, a Senior Software Engineer on the Netflix Edge Platform team, will discuss how by leveraging a reactive stream-based protocol,...
In a recent post, titled “10 Surprising Facts About Cloud Computing and What It Really Is”, Zac Johnson highlighted some interesting facts about cloud computing in the SMB marketplace: Cloud Computing is up to 40 times more cost-effective for an SMB, compared to running its own IT system. 94% of SMBs have experienced security benefits in the cloud that they didn’t have with their on-premises service
The dynamic nature of the cloud means that change is a constant when it comes to modern cloud-based infrastructure. Delivering modern applications to end users, therefore, is a constantly shifting challenge. Delivery automation helps IT Ops teams ensure that apps are providing an optimal end user experience over hybrid-cloud and multi-cloud environments, no matter what the current state of the infrastructure is. To employ a delivery automation strategy that reflects your business rules, making r...
"We started a Master of Science in business analytics - that's the hot topic. We serve the business community around San Francisco so we educate the working professionals and this is where they all want to be," explained Judy Lee, Associate Professor and Department Chair at Golden Gate University, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Gone are the days when application development was the daunting task of the highly skilled developers backed with strong IT skills, low code application development has democratized app development and empowered a new generation of citizen developers. There was a time when app development was in the domain of people with complex coding and technical skills. We called these people by various names like programmers, coders, techies, and they usually worked in a world oblivious of the everyday pri...
The “Digital Era” is forcing us to engage with new methods to build, operate and maintain applications. This transformation also implies an evolution to more and more intelligent applications to better engage with the customers, while creating significant market differentiators. In both cases, the cloud has become a key enabler to embrace this digital revolution. So, moving to the cloud is no longer the question; the new questions are HOW and WHEN. To make this equation even more complex, most ...