|By Richard (Rik) Brooks||
|March 6, 2013 02:00 PM EST||
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.
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:
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:
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:
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.
Ll_customer_id = dw_detail.getItemNumber(dw_detail.getRow(), "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.
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.
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.
Datastore ld_security, ld_events
ld _secutity = create datastore
ld_events = create datastore
ld_events.dataobject = "d_events"
ld_security.dataobject = "d_get_security"
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.
|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.
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
Sep. 30, 2016 12:45 PM EDT Reads: 2,696
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Sep. 30, 2016 12:45 PM EDT Reads: 4,479
Sep. 30, 2016 12:30 PM EDT Reads: 2,257
From wearable activity trackers to fantasy e-sports, data and technology are transforming the way athletes train for the game and fans engage with their teams. In his session at @ThingsExpo, will present key data findings from leading sports organizations San Francisco 49ers, Orlando Magic NBA team. By utilizing data analytics these sports orgs have recognized new revenue streams, doubled its fan base and streamlined costs at its stadiums. John Paul is the CEO and Founder of VenueNext. Prior ...
Sep. 30, 2016 12:30 PM EDT Reads: 3,263
Businesses are struggling to manage the information flow and interactions between all of these new devices and things jumping on their network, and the apps and IT systems they control. The data businesses gather is only helpful if they can do something with it. In his session at @ThingsExpo, Chris Witeck, Principal Technology Strategist at Citrix, will discuss how different the impact of IoT will be for large businesses, expanding how IoT will allow large organizations to make their legacy ap...
Sep. 30, 2016 12:30 PM EDT Reads: 475
“We're a global managed hosting provider. Our core customer set is a U.S.-based customer that is looking to go global,” explained Adam Rogers, Managing Director at ANEXIA, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Sep. 30, 2016 12:15 PM EDT Reads: 3,219
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
Sep. 30, 2016 11:30 AM EDT Reads: 5,157
What does it look like when you have access to cloud infrastructure and platform under the same roof? Let’s talk about the different layers of Technology as a Service: who cares, what runs where, and how does it all fit together. In his session at 18th Cloud Expo, Phil Jackson, Lead Technology Evangelist at SoftLayer, an IBM company, spoke about the picture being painted by IBM Cloud and how the tools being crafted can help fill the gaps in your IT infrastructure.
Sep. 30, 2016 11:15 AM EDT Reads: 3,091
Developing software for the Internet of Things (IoT) comes with its own set of challenges. Security, privacy, and unified standards are a few key issues. In addition, each IoT product is comprised of (at least) three separate application components: the software embedded in the device, the back-end service, and the mobile application for the end user’s controls. Each component is developed by a different team, using different technologies and practices, and deployed to a different stack/target –...
Sep. 30, 2016 11:15 AM EDT Reads: 1,568
One of biggest questions about Big Data is “How do we harness all that information for business use quickly and effectively?” Geographic Information Systems (GIS) or spatial technology is about more than making maps, but adding critical context and meaning to data of all types, coming from all different channels – even sensors. In his session at @ThingsExpo, William (Bill) Meehan, director of utility solutions for Esri, will take a closer look at the current state of spatial technology and ar...
Sep. 30, 2016 11:00 AM EDT Reads: 504
According to Forrester Research, every business will become either a digital predator or digital prey by 2020. To avoid demise, organizations must rapidly create new sources of value in their end-to-end customer experiences. True digital predators also must break down information and process silos and extend digital transformation initiatives to empower employees with the digital resources needed to win, serve, and retain customers.
Sep. 30, 2016 11:00 AM EDT Reads: 553
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, wh...
Sep. 30, 2016 11:00 AM EDT Reads: 3,993
Complete Internet of Things (IoT) embedded device security is not just about the device but involves the entire product’s identity, data and control integrity, and services traversing the cloud. A device can no longer be looked at as an island; it is a part of a system. In fact, given the cross-domain interactions enabled by IoT it could be a part of many systems. Also, depending on where the device is deployed, for example, in the office building versus a factory floor or oil field, security ha...
Sep. 30, 2016 10:45 AM EDT Reads: 775
Ask someone to architect an Internet of Things (IoT) solution and you are guaranteed to see a reference to the cloud. This would lead you to believe that IoT requires the cloud to exist. However, there are many IoT use cases where the cloud is not feasible or desirable. In his session at @ThingsExpo, Dave McCarthy, Director of Products at Bsquare Corporation, will discuss the strategies that exist to extend intelligence directly to IoT devices and sensors, freeing them from the constraints of ...
Sep. 30, 2016 10:45 AM EDT Reads: 2,761
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lea...
Sep. 30, 2016 10:30 AM EDT Reads: 592
24Notion is full-service global creative digital marketing, technology and lifestyle agency that combines strategic ideas with customized tactical execution. With a broad understand of the art of traditional marketing, new media, communications and social influence, 24Notion uniquely understands how to connect your brand strategy with the right consumer. 24Notion ranked #12 on Corporate Social Responsibility - Book of List.
Sep. 30, 2016 10:30 AM EDT Reads: 266
Sep. 30, 2016 10:30 AM EDT Reads: 273
SYS-CON Events announced today that CDS Global Cloud, an Infrastructure as a Service provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. CDS Global Cloud is an IaaS (Infrastructure as a Service) provider specializing in solutions for e-commerce, internet gaming, online education and other internet applications. With a growing number of data centers and network points around the world, ...
Sep. 30, 2016 10:30 AM EDT Reads: 3,037
SYS-CON Events announced today that LeaseWeb USA, a cloud Infrastructure-as-a-Service (IaaS) provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LeaseWeb is one of the world's largest hosting brands. The company helps customers define, develop and deploy IT infrastructure tailored to their exact business needs, by combining various kinds cloud solutions.
Sep. 30, 2016 10:15 AM EDT Reads: 3,361
Technology vendors and analysts are eager to paint a rosy picture of how wonderful IoT is and why your deployment will be great with the use of their products and services. While it is easy to showcase successful IoT solutions, identifying IoT systems that missed the mark or failed can often provide more in the way of key lessons learned. In his session at @ThingsExpo, Peter Vanderminden, Principal Industry Analyst for IoT & Digital Supply Chain to Flatiron Strategies, will focus on how IoT de...
Sep. 30, 2016 10:15 AM EDT Reads: 1,297