Welcome!

Cloud Expo Authors: Michael Meiner, Carmen Gonzalez, Elizabeth White, Liz McMillan, Pat Romanski

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.

@CloudExpo Stories
The 4th International DevOps Summit, co-located with16th International Cloud Expo – being held June 9-11, 2015, at the Javits Center in New York City, NY – announces that its Call for Papers is now open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's large...
Verizon Enterprise Solutions is simplifying the cloud-purchasing experience for its clients, with the launch of Verizon Cloud Marketplace, a key foundational component of the company's robust ecosystem of enterprise-class technologies. The online storefront will initially feature pre-built cloud-based services from AppDynamics, Hitachi Data Systems, Juniper Networks, PfSense and Tervela. Available globally to enterprises using Verizon Cloud, Verizon Cloud Marketplace provides a one-stop shop fo...
Leysin American School is an exclusive, private boarding school located in Leysin, Switzerland. Leysin selected an OpenStack-powered, private cloud as a service to manage multiple applications and provide development environments for students across the institution. Seeking to meet rigid data sovereignty and data integrity requirements while offering flexible, on-demand cloud resources to users, Leysin identified OpenStack as the clear choice to round out the school's cloud strategy. Additional...
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com...
We are all here because we are sold on the transformative promise of The Cloud. But what good is all of this ephemeral, on-demand infrastructure if your usage doesn't actually improve the agility and speed of your business? How must Operations adapt in order to avoid stifling your Cloud initiative? In his session at DevOps Summit, Damon Edwards, co-founder and managing partner of the DTO Solutions, will highlight the successful organizational, process, and tooling patterns of high-performing c...
The definition of IoT is not new, in fact it’s been around for over a decade. What has changed is the public's awareness that the technology we use on a daily basis has caught up on the vision of an always on, always connected world. If you look into the details of what comprises the IoT, you’ll see that it includes everything from cloud computing, Big Data analytics, “Things,” Web communication, applications, network, storage, etc. It is essentially including everything connected online from ha...
Software-driven innovation is becoming a primary approach to how businesses create and deliver new value to customers. A survey of 400 business and IT executives by the IBM Institute for Business Value showed businesses that are more effective at software delivery are also more profitable than their peers nearly 70 percent of the time (1). DevOps provides a way for businesses to remain competitive, applying lean and agile principles to software development to speed the delivery of software that ...
Docker offers a new, lightweight approach to application portability. Applications are shipped using a common container format and managed with a high-level API. Their processes run within isolated namespaces that abstract the operating environment independently of the distribution, versions, network setup, and other details of this environment. This "containerization" has often been nicknamed "the new virtualization." But containers are more than lightweight virtual machines. Beyond their small...
The move in recent years to cloud computing services and architectures has added significant pace to the application development and deployment environment. When enterprise IT can spin up large computing instances in just minutes, developers can also design and deploy in small time frames that were unimaginable a few years ago. The consequent move toward lean, agile, and fast development leads to the need for the development and operations sides to work very closely together. Thus, DevOps become...
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's

An entirely new security model is needed for the Internet of Things, or is it? Can we save some old and tested controls for this new and different environment? In his session at @ThingsExpo, New York's at the Javits Center, Davi Ottenheimer, EMC Senior Director of Trust, reviewed hands-on lessons with IoT devices and reveal a new risk balance you might not expect. Davi Ottenheimer, EMC Senior Director of Trust, has more than nineteen years' experience managing global security operations and asse...
Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Ar...
Technology is enabling a new approach to collecting and using data. This approach, commonly referred to as the "Internet of Things" (IoT), enables businesses to use real-time data from all sorts of things including machines, devices and sensors to make better decisions, improve customer service, and lower the risk in the creation of new revenue opportunities. In his General Session at Internet of @ThingsExpo, Dave Wagstaff, Vice President and Chief Architect at BSQUARE Corporation, discuss the ...
The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, a...
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
"Our premise is Docker is not enough. That's not a bad thing - we actually love Docker. At ActiveState all our products are based on open source technology and Docker is an up-and-coming piece of open source technology," explained Bart Copeland, President & CEO of ActiveState Software, in this SYS-CON.tv interview at DevOps Summit at Cloud Expo®, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
DevOps Summit 2015 New York, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete...
Infor has announced a new feature Infor CloudSuite™ Aerospace & Defense (A&D) to aid compliance with International Traffic in Arms Regulations (ITAR). The ITAR function will serve as a complementary function for new or existing Infor CloudSuite A&D customers, to facilitate compliance for Infor customers that are creating a US defense article or performing a US defense service and wish to benefit from cloud-services. The ITAR regulation serves to manage handling and access requirements for dat...
What do a firewall and a fortress have in common? They are no longer strong enough to protect the valuables housed inside. Like the walls of an old fortress, the cracks in the firewall are allowing the bad guys to slip in - unannounced and unnoticed. By the time these thieves get in, the damage is already done and the network is already compromised. Intellectual property is easily slipped out the back door leaving no trace of forced entry. If we want to reign in on these cybercriminals, it's hig...