Welcome!

Silverlight Authors: Steven Mandel, Gerardo A Dada, Srinivasan Sundara Rajan, Yeshim Deniz, Greg O'Connor

Blog Feed Post

PB Event Order

PowerBuilder - Events and Precedence


     The order in which events happen within a PowerBuilder Classic application is in most cases, a very predictable model. The PB developer should be aware of this aspect when developing GUI based applications. For instance, when focus is shifted from one object to another object, the first object will experience the Modified and LoseFocus events before the second object experiences a get focus event.

To understand this further, consider the following scenarios and the resulting events.
 

An Application starts and window "A" is opened

APPLICATION OPEN
WINDOW "A" OPEN
WINDOW "A" ACTIVATE
CHILD OBJECT GET FOCUS (First object in tab order)
 

Window "B" is opened (Window "A" stays open)

WINDOW "A" CURRENT OBJECT LOSE FOCUS
WINDOW "A" DEACTIVATE
WINDOW "B" OPEN
WINDOW "B" ACTIVATE
WINDOW "B" CHILD OBJECT GET FOCUS (First object in tab order)

Window "B" closed, return to Window "A".

WINDOW "B" CLOSEQUERY
WINDOW "B" CURRENT OBJECT LOSE FOCUS
WINDOW "B" CLOSE
WINDOW "B" DEACTIVATE
WINDOW "A" ACTIVATE
OBJECT GET FOCUS (Last object that had focus)
 

"Click" on new object within Same Window

OBJECT 1 MODIFIED (if changed)
OBJECT 1 LOSE FOCUS
OBJECT 2 GET FOCUS
OBJECT 2 CLICKED
 

"Tab" to new object within Same Window

OBJECT 1 MODIFIED (if changed)
OBJECT 1 LOSE FOCUS
OBJECT 2 GET FOCUS (next object in tab order)

Interestingly enough, events can and will occur even when no actions are performed by the user. If you are
using a screen saver, such as the one in Windows, the following will happen.

Flip to screen saver (After period of inactivity)
   WINDOW DEACTIVATE
   OBJECT LOSE FOCUS
Return from screen saver
   WINDOW ACTIVATE
   OBJECT GET FOCUS


DataWindows and Events

A DataWindow is a single object within a window. As such, events happen to the DataWindow as a single object (DW COntrol) and not to the individual items that are within the DataWindow object itself. In order to make up for this, there are a number of special events that exist only for DataWindows. These events are not quite the same as those of other Window objects and therefore must be considered on their own.

Consider the following scenario:

The User Clicks on a field in a data window, keys something, clicks on another field within the data window, keys something and then clicks on a Command Button (outside of the DataWindow). The sequence of DataWindow events is as follows:

DW GET FOCUS
DW CLICKED
DW EDIT CHANGED (once for each keystroke)
DW CLICKED
DW ITEMCHANGED
DW ITEM FOCUS CHANGED
DW EDIT CHANGED (once for each keystroke)
DW LOSE FOCUS

COMMAND BUTTON GET FOCUS
COMMAND BUTTON CLICKED

A number of significant aspects are happening at this time! For example: there was only one get focus and one lose focus event. Only one item changed event occurred (even though two items were changed). A clicked event occurred two times. One edit changed event occurred for every keystroke made within the DataWindow.

If DataWindow edits were behind the two modified fields, only the first field would have been edited. For all intents and purposes, the second field has nothing in it!

Now let us insert the ACCEPTTEXT() function into the command button Clicked script. Now the sequence of events flows as follows:

DW GET FOCUS
DW CLICKED
DW EDIT CHANGED (once for each keystroke)
DW CLICKED
DW ITEMCHANGED
DW ITEM FOCUS CHANGED
DW EDIT CHANGED (once for each keystroke)
DW LOSE FOCUS

COMMAND BUTTON GET FOCUS
COMMAND BUTTON CLICKED

DW ITEMCHANGED

The last item changed event was triggered by the AcceptText ( ) functionality. You might be tempted to put this function in the DataWindow Control's losefocus event script, but this makes it very difficult for a user to cancel a transaction when they can not get past the edit rule!
 

Events Precedence Table

The following is a table that shows the order of events for each object type:

Objects Events Order Notes

Window
Open 1
Activate 2 Also after closing of
another Window
Key 3 Each Keystroke (not all objects)
CloseQuery 4
Close 5
Deactivate 6

Single Line Edit, Multi Line Edit
Get Focus 1
Modified 2
LoseFocus 3

List Box, Drop Down List Box
GetFocus 1
SelectionChanged 2 When choice made from list
Modified 3
DoubleClicked 4 Only possible when "always show
list box" is active
LoseFocus 5

Static Text, Picture, Picture Button
GetFocus 1
Clicked 2
DoubleClicked 3 Always issues a Clicked event first
LoseFocus 4

Check Box, Command Button, Radio Button
GetFocus 1
Clicked 2
LoseFocus 3

DataWindow
GetFocus 1
Clicked 2
DoubleClicked 3 Always issues a Clicked event first
EditChanged 4 Once for each keystroke
ItemError 5 When item doesn't pass validation
ItemChanged 6 When object loses focus within dw
RowFocusChanged 7
ItemFocusChanged 8
LoseFocus 9
 

Events Notes

Triggerevent Function

At any time in an application, an event can occur through use of the TRIGGEREVENT() function. This can be a very handy thing to know and use. It can also cause problems if the application is counting on certain events to occur in a certain sequence.

DataWindow Clicked Event

Often, the clicked event in a data window is used to trigger a choice made by the user. In the script for this event it is always a good policy to check that the clicked row value is greater than zero. If the click is made on the borders or white space of a data window, the GETCLICKEDROW function will return a zero.

Although the ItemError! event listed after EditChanged! event under dw events order is a bit confusing, I am
sure it is correct as per the 4 phases of validation:

. edit-changed check
. data-type check (ItemError! fires here...)
. item-changed check
. validation-rule check

***********************************************************
Note: You can not safely predict the event model in PB.Net applications as the object drawing and interaction is outside the application's control in the WPF layer of the O/S. WPF controls all aspects of event handling and even imposes restrictions for the PB.Net application! 
***********************************************************

Regards ... Chris

Read the original blog entry...

More Stories By Chris Pollach

Chris Pollach is a Senior Consultant with over 30 years experience in Systems and Software Analysis, Development, Maintenance and Technical Support, mainly in the areas of GUI Design, MS-Windows Programming, Java / .NET Programming, Wireless, Application / Web Server Design & Programming, Object Oriented Development Tools and Methodologies, Data Base, Data Communications and Network application development. He has participated in numerous technical, planning and management roles, as well as consulted and educated in these fields for a diverse clientele. He is also the owner of “Software Tool & Die Inc.” a company dedicated to provide custom software and education solutions on Object Oriented business systems.

As an educator, Chris is certified to teach PowerBuilder (first in Canada), MS-SQLServer, Sybase’s Enterprise Application Studio and EAServer integrated application/web development environment. He is former Certified SilverStream developer (CSSD) and current Certified PowerBuilder Developer – Associate / Professional (CPD-P) as well as a Certified Sybase Tools Instructor (CSI).

Chris has written numerous articles in various popular personal computer magazines, newsletters and is the author of the PowerGuide and PowerExpert products as well as the STD Foundation Classes. Currently, Chris has developed a Foundation Class library for Sybase's PocketBuilder, SAP's PowerBulder and EAServer products and now Appeon Web & mobile products that integrates JSP or ASP web development, Section 508 / CLF web standards and mobile applications. A new Web Service framework has also been released for IIs to support PowerBuilder based web service NVUO's!

Chris recently became a 2nd Degree Black in the TaeKwonDo martial art and has developed a Martial Art multimedia study guide using the Component-One “Doc2Help” and Sybase PowerBuilder products. Since the fall of 2004 he became a TaeKwonDo instructor for the City of Ottawa’s Goulbourn program. He has also been certified with the World TaeKwonDo Federation (February 2005 - 1st Dan and October 2008 - 2nd Dan).

Chris was awarded the Sybase “Innovation and Achievement” award for 2005 as voted for by the International Sybase User Group (ISUG). This award was presented for innovations to the PocketBuilder mobile development product, contributions to the PowerBuilder News groups and support of the Ottawa Sybase User Group.

To round his management and leadership skills, Chris is the former president of the Kiwanis Club of Goulbourn and still volunteers his time with the service clubs in his area. He is also the coordinator of the Ottawa Sybase User group and a certified NAUI scuba instructor. For the last three years, Chris has been voted onto the ISUG Board of Directors and holds the position of "Director - North American User Groups".

@ThingsExpo Stories
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, discussed the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
WebRTC defines no default signaling protocol, causing fragmentation between WebRTC silos. SIP and XMPP provide possibilities, but come with considerable complexity and are not designed for use in a web environment. In his session at @ThingsExpo, Matthew Hodgson, technical co-founder of the Matrix.org, discussed how Matrix is a new non-profit Open Source Project that defines both a new HTTP-based standard for VoIP & IM signaling and provides reference implementations.
The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound e...
We all know that data growth is exploding and storage budgets are shrinking. Instead of showing you charts on about how much data there is, in his General Session at 17th Cloud Expo, Scott Cleland, Senior Director of Product Marketing at HGST, showed how to capture all of your data in one place. After you have your data under control, you can then analyze it in one place, saving time and resources.
910Telecom exhibited at the 19th International Cloud Expo, which took place at the Santa Clara Convention Center in Santa Clara, CA, in November 2016. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and exchanges.
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...
Web Real-Time Communication APIs have quickly revolutionized what browsers are capable of. In addition to video and audio streams, we can now bi-directionally send arbitrary data over WebRTC's PeerConnection Data Channels. With the advent of Progressive Web Apps and new hardware APIs such as WebBluetooh and WebUSB, we can finally enable users to stitch together the Internet of Things directly from their browsers while communicating privately and securely in a decentralized way.
The IoT industry is now at a crossroads, between the fast-paced innovation of technologies and the pending mass adoption by global enterprises. The complexity of combining rapidly evolving technologies and the need to establish practices for market acceleration pose a strong challenge to global enterprises as well as IoT vendors. In his session at @ThingsExpo, Clark Smith, senior product manager for Numerex, discussed how Numerex, as an experienced, established IoT provider, has embraced a new m...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo 2016 in New York. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place June 6-8, 2017, at the Javits Center in New York City, New York, is co-located with 20th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry p...
SYS-CON Events announced today that CA Technologies has been named "Platinum Sponsor" of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, New York, and 21st International Cloud Expo, which will take place in November in Silicon Valley, California.
As organizations realize the scope of the Internet of Things, gaining key insights from Big Data, through the use of advanced analytics, becomes crucial. However, IoT also creates the need for petabyte scale storage of data from millions of devices. A new type of Storage is required which seamlessly integrates robust data analytics with massive scale. These storage systems will act as “smart systems” provide in-place analytics that speed discovery and enable businesses to quickly derive meaningf...
With billions of sensors deployed worldwide, the amount of machine-generated data will soon exceed what our networks can handle. But consumers and businesses will expect seamless experiences and real-time responsiveness. What does this mean for IoT devices and the infrastructure that supports them? More of the data will need to be handled at - or closer to - the devices themselves.
The Internet of Things can drive efficiency for airlines and airports. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Sudip Majumder, senior director of development at Oracle, discussed the technical details of the connected airline baggage and related social media solutions. These IoT applications will enhance travelers' journey experience and drive efficiency for the airlines and the airports.
SYS-CON Events announced today that delaPlex will exhibit at SYS-CON's @CloudExpo, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. delaPlex pioneered Software Development as a Service (SDaaS), which provides scalable resources to build, test, and deploy software. It’s a fast and more reliable way to develop a new product or expand your in-house team.
In 2014, Amazon announced a new form of compute called Lambda. We didn't know it at the time, but this represented a fundamental shift in what we expect from cloud computing. Now, all of the major cloud computing vendors want to take part in this disruptive technology. In his session at 20th Cloud Expo, John Jelinek IV, a web developer at Linux Academy, will discuss why major players like AWS, Microsoft Azure, IBM Bluemix, and Google Cloud Platform are all trying to sidestep VMs and containers...
You think you know what’s in your data. But do you? Most organizations are now aware of the business intelligence represented by their data. Data science stands to take this to a level you never thought of – literally. The techniques of data science, when used with the capabilities of Big Data technologies, can make connections you had not yet imagined, helping you discover new insights and ask new questions of your data. In his session at @ThingsExpo, Sarbjit Sarkaria, data science team lead ...
SYS-CON Events announced today that CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
In his session at @ThingsExpo, Sudarshan Krishnamurthi, a Senior Manager, Business Strategy, at Cisco Systems, will discuss how IT and operational technology (OT) work together, as opposed to being in separate siloes as once was traditional. Attendees will learn how to fully leverage the power of IoT in their organization by bringing the two sides together and bridging the communication gap. He will also look at what good leadership must entail in order to accomplish this, and how IT managers ca...
The best way to leverage your Cloud Expo presence as a sponsor and exhibitor is to plan your news announcements around our events. The press covering Cloud Expo and @ThingsExpo will have access to these releases and will amplify your news announcements. More than two dozen Cloud companies either set deals at our shows or have announced their mergers and acquisitions at Cloud Expo. Product announcements during our show provide your company with the most reach through our targeted audiences.
DevOps is being widely accepted (if not fully adopted) as essential in enterprise IT. But as Enterprise DevOps gains maturity, expands scope, and increases velocity, the need for data-driven decisions across teams becomes more acute. DevOps teams in any modern business must wrangle the ‘digital exhaust’ from the delivery toolchain, "pervasive" and "cognitive" computing, APIs and services, mobile devices and applications, the Internet of Things, and now even blockchain. In this power panel at @...