Question on program structure about event handling in nested JPanels in GUI

Hi All,
I'm currently writing a GUI app with a wizard included in the app. I have one class that acts as a template for each of the panels in the wizard. That class contains a JPanel called contentsPanel that I intend to put the specific contents into. I also want the panel contents to be modular so I have a couple of classes for different things, e.g. name and address panel, etc. these panels will contain checkboxes and the like that I want to event listeneres to watch out for. Whats the best way of implementing event handling for panel within panel structure? E.g for the the checkbox example,would it be a good idea to have an accessor method that returns the check book object from the innerclass/panel and use an addListener() method on the returned object in the top level class/panel. Or is it better to have the event listeners for those objects in the same class? I would appreciate some insight into this?
Regards!

MyMainClass.main(new String[] { "the", "arguments" });
// or, if you defined your main to use varags (i.e. as "public static void main(String... args)") then you can just use
MyMainClass.main("the", "arguments");But you should really extract your functionality out of the main method into meaningful classes and methods and just use those from both your console code and your GUI code.

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Questions from a rookie about event structures

Hello,
I am currently scheduled for Labview classes next month,
so I want to apologize in advance for "dumb questions". I have created
a program that is starting
to be a CPU resource hog. The majority of my program is inside a while
loop so that the program will "react" to changes in controls, etc. I am
assuming that
if I incorporate "event structures" in my program that my program will
not be a resource hog. Is the use of event structures the correct
way to go? If using
event structures is the correct way to go, what is the best way to
learn how to incorporate "event structures"? I am assuming that
the examples in Labview will show me how. Are there any good reading
materials about event structures?
Regards,
Kaspar

To fix the CPU resource issue, you need to place a small wait statement in your loop. It will solve two problems:
Slow down the loop (you don't need to check for UI changes more that 10x/second)
It will allow other, parallel tasks a chance to run after each iteration. Without a wait, it will hog the CPU for 55ms before releasing control.
If your loop currently spins one million times a second and you would place a 1ms wait, the CPU would go from 100% to 0.1%!
The event structure is a fantastic tool to solve most UI issues and it makes the diagram automatically simpler, more self-documenting and easier to read. Have a look at some of the examples that ship with LabVIEW.
The event structure is easy to learn, so dive right in. Read the online help for some important considerations. As a rule of thumb you should stick to a single event structure per diagram.
LabVIEW Champion . Do more with less code and in less time .

Question about event handling in JComponents

I have often found it useful to create a component that acts as an event handler for events the component generates itself. For example, a panel that listens for focus events that effect it and handle these events internally. (See below).
My question is: Can this practice cause synchronization issues or any other type of problem that I need to watch out for? Is it good/bad or neither. Are there any issues I should be aware of?
Thanks in advance for the help.
Example:
public class qPanel extends JPanel implements FocusListener
public qPanel () {
super.addFocusListener(this);
public void focusGained(FocusEvent e) {
//Do stuff
public void focusLost(FocusEvent e) {
//Do stuff
}

Hi,
Handling events this way is completely fine and saves on number of classes. Only thing you may want to watch out for is that the handler methods have to be public. This means that someone could use your component and call one of the methods. For example, I could write:
panel.focusGained(new FocusEvent(....))
when it's not really gaining focus. So, if you're writing this component for re-use you might want to be aware of this.
An alternative:
Use a single internal class to handle all events. It can then delegate to private methods of your component. Example:
class MyEventHandler implements FocusListener, MouseListener, etc... {
public void focusGained(FocusEvent fe) {
doFocusGained(fe);
public void mousePressed(MouseEvent me) {
doMousePressed(me);
Then your component could have:
private void doFocusGained(FocusEvent fe) {
private void doMousePressed(MouseEvent me) {
etc...
Just ideas :)
Thanks!
Shannon Hickey (Swing Team)
I have often found it useful to create a component
that acts as an event handler for events the component
generates itself. For example, a panel that listens
for focus events that effect it and handle these
events internally. (See below).
My question is: Can this practice cause
synchronization issues or any other type of problem
that I need to watch out for? Is it good/bad or
neither. Are there any issues I should be aware of?
Thanks in advance for the help.
Example:
public class qPanel extends JPanel implements
FocusListener
public qPanel () {
super.addFocusListener(this);
public void focusGained(FocusEvent e) {
//Do stuff
public void focusLost(FocusEvent e) {
//Do stuff

About event handler

hi
i am trying to develop a event handler for all the attributes of a resource that when user is modified is attributes. he need get a notification that paritcular attribute or u r data is modified..
actually i have seen that they have return adapter for each attribute but dont want so many adapters to be writtten so i want to develop a event handler for that scenario... please provide the sample code so that i can modifie or re coding it....
thanks
avinash

Hi,
I had created one dissconnected resource and one application form for it... the user had filled the form of that resource and submitted and when he want to update the form once again the event handler should be tirrger and paritcular attribute should be update and he had to send email notification that attribute is changed...
here is once thing that if he had change numberof attributes at a time but we have to send only one email notification for all the attributes...
regards
avinash

About Event Handling in user Defined Form (In Addon)

Hi Every One,
Can Anyone Give Me Notes On EventHandling in forms That are Disgened using Sdk UIAPI .Like Button event ,application event, menuevent... etc with saple code
Regards
Srinivas

Hi Sura,
Hope this helps. C# sample code.
//   SAP MANAGE UI API 2005 SDK Sample
//   File:      CatchingEvents.cs
//   Copyright (c) SAP MANAGE
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF
// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A
// PARTICULAR PURPOSE.
// BEFORE STARTING:
// 1. Add reference to the "SAP Business One UI API"
// 2. Insert the development connection string to the "Command line argument"
// 1.
//     a. Project->Add Reference...
//     b. select the "SAP Business One UI API 2005" From the COM folder
// 2.
//      a. Project->Properties...
//      b. choose Configuration Properties folder (place the arrow on Debugging)
//      c. place the following connection string in the 'Command line arguments' field
// 0030002C0030002C00530041005000420044005F00440061007400650076002C0050004C006F006D0056004900490056
using System;
using System.Windows.Forms;
class CatchingEvents {
    // This parameter will use us to manipulate the
    // SAP Business One Application
    private SAPbouiCOM.Application SBO_Application;
    private void SetApplication() {
        // Use an SboGuiApi object to establish connection
        // with the SAP Business One application and return an
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        SAPbouiCOM.SboGuiApi SboGuiApi = null;
        string sConnectionString = null;
        SboGuiApi = new SAPbouiCOM.SboGuiApi();
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        // statment should be suficient for either development or run mode
        sConnectionString = System.Convert.ToString( Environment.GetCommandLineArgs().GetValue( 1 ) );
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        SboGuiApi.Connect( sConnectionString );
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        SBO_Application = SboGuiApi.GetApplication( -1 );
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        // set SBO_Application with an initialized application object
        SetApplication();
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        SBO_Application.AppEvent += new SAPbouiCOM._IApplicationEvents_AppEventEventHandler( SBO_Application_AppEvent );
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        SBO_Application.MenuEvent += new SAPbouiCOM._IApplicationEvents_MenuEventEventHandler( SBO_Application_MenuEvent );
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        SBO_Application.ItemEvent += new SAPbouiCOM._IApplicationEvents_ItemEventEventHandler( SBO_Application_ItemEvent );
        // events handled by SBO_Application_ProgressBarEvent
        SBO_Application.ProgressBarEvent += new SAPbouiCOM._IApplicationEvents_ProgressBarEventEventHandler( SBO_Application_ProgressBarEvent );
        // events handled by SBO_Application_StatusBarEvent
        SBO_Application.StatusBarEvent += new SAPbouiCOM._IApplicationEvents_StatusBarEventEventHandler( SBO_Application_StatusBarEvent );
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        // (Ignore aet_ServerTermination)
        // in order to implement your own code upon each of the events
        // place you code instead of the matching message box statement
        switch ( EventType ) {
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                // Take care of terminating your AddOn application
                System.Windows.Forms.Application.Exit();
                break;
            case SAPbouiCOM.BoAppEventTypes.aet_CompanyChanged:
                SBO_Application.MessageBox( "A Company Change Event has been caught", 1, "Ok", "", "" );
                // Check the new company name, if your add on was not meant for
                // the new company terminate your AddOn
                //     If SBO_Application.Company.Name Is Not "Company1" then
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                break;
            case SAPbouiCOM.BoAppEventTypes.aet_LanguageChanged:
                SBO_Application.MessageBox( "A Languge Change Event has been caught", 1, "Ok", "", "" );
                break;
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        // process the menu event by your self
        // change BubbleEvent to False so that SAP Business One won't process it
        BubbleEvent = true;
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            // unmark the following statement
            // BubbleEvent = False
        else {
            SBO_Application.SetStatusBarMessage( "Menu item: " + pVal.MenuUID + " sent an event AFTER SAP Business One processes it.", SAPbouiCOM.BoMessageTime.bmt_Long, true );
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        // BubbleEvent sets the behavior of SAP Business One.
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        BubbleEvent = true;
        if ( pVal.FormType != 0 ) {
            // the message box form type is 0
            // I chose not to deal with events triggered by a message box
            // every event will open a message box with the event
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            SAPbouiCOM.BoEventTypes EventEnum = 0;
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            if ( ( EventEnum != SAPbouiCOM.BoEventTypes.et_FORM_ACTIVATE ) & ( EventEnum != SAPbouiCOM.BoEventTypes.et_FORM_LOAD ) ) {
                SBO_Application.MessageBox( "An " + EventEnum.ToString() + " has been sent by a form with the unique ID: " + FormUID, 1, "Ok", "", "" );
    private void SBO_Application_ProgressBarEvent( ref SAPbouiCOM.ProgressBarEvent pVal, out bool BubbleEvent) {
        SAPbouiCOM.BoProgressBarEventTypes EventEnum = 0;
        EventEnum = pVal.EventType;
        BubbleEvent = true;
        SBO_Application.MessageBox( "The event " + EventEnum.ToString() + " has been sent", 1, "Ok", "", "" );
    private void SBO_Application_StatusBarEvent( string Text, SAPbouiCOM.BoStatusBarMessageType MessageType ) {
        SBO_Application.MessageBox( @"Status bar event with message: """ + Text + @""" has been sent", 1, "Ok", "", "" );
Regards,
Jay.

Question about event handling in a button

I recently coded a console version of my java program (just outputs stuff into the system console and a logger). I am now adding a simple GUI with a set of buttons to start and stop the program. In order to do this, do I just copy paste the main function contents of the console version of my code into the button's event handlers or is there a way I can just run the main class? I was googling for Class loading in java but I'm not sure if this is what I should be looking at... Can someone please help me out?

MyMainClass.main(new String[] { "the", "arguments" });
// or, if you defined your main to use varags (i.e. as "public static void main(String... args)") then you can just use
MyMainClass.main("the", "arguments");But you should really extract your functionality out of the main method into meaningful classes and methods and just use those from both your console code and your GUI code.

Problem about event handling or dispatching

I created a JFrame with a JButton in it. A keyListener is add to the jframe.
Key events can be catched if JDK1.3.1_08 is employed. However, it doesn't work if JDK1.4.1_02 is empolyed. Can anyone tell me the problem? Thanks a lot!
The following is the source code:
public class drawa extends JFrame implements KeyListener
public static void main(String[] args) {
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public drawa() {
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     addKeyListener(this);
     setSize(500,450);
     setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     setVisible(true);
public void keyPressed(KeyEvent evt){
     System.out.println("a");
public void keyTyped(KeyEvent evt){}
public void keyReleased(KeyEvent evt){}

Your frame must return true for isFocusable ().
Kind regards,
  Levi

About event handling

Hi
I am using jdev11.1.1.5.0
I created a search page in jspx page
I put there a inputText in which user enter a value and there is a command button named search which perform search operation which is defined in backing.
Now I want to add a listener that after entering value into input text component user press enter and search should be perform properly
How can I do the same.?
Thanks

Hi Arun
Thanks for your solution but i need something else
I already have a separate method for search.
and i do not want to filter table on input time
My need is when user have entered the search value in inputtext after that either by pressing enter key by keyboard or by pressing search button on screen ,search should be performed

How can I execute an external program from within a button's event handler?

I am using Tomcat ApacheTomcat 6.0.16 with Netbeans 6.1 (with the latest JDK/J2EE)
I need to execute external programs from an event handler for a button on a JSF page (the program is compiled, and extremely fast compared both to plain java and especially stored procedures written in SQL).
I tried what I'd do in a standalone program (as shown in the appended code), but it didn't work. Instead I received text saying the program couldn't be found. This error message comes even if I try the Windows command "dir". I thought with 'dir' I'd at least get the contents of the current working directory. :-(
I can probably get by with cgi on Apache's httpd server (or, I understand tomcat supports cgi, but I have yet to get that to work either), but whatever I do I need to be able to do it from within the button's event handler. And if I resort to cgi, I must be able to maintain session jumping from one server to the other and back.
So, then, how can I do this?
Thanks
Ted
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Hi Fonsi!
One way to execute an external program is to use the System Exec.vi. You find it in the functions pallet under Communication.
/Thomas

Multiple event-handling threads?

I am writing a Java program that will launch other Java programs within the same JVM. This feature is for an RAD IDE that currently uses Runtime.exec.
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Is there any way to tell the JVM to use different event-handling threads for my application? Alternatively, does anybody know of any obscure functions I could use to maybe cause the event-handling thread to delegate processing to another one of my own threads? Ugly hacks are welcome.

After I first posted this question, I've taken a look at the java.awt.EventQueue class. The API provides an easy way to use your own EventQueue that could possibly dispatch events with multiple threads. If you make sure that you only use one thread at a time for each virtual JVM, I don't think that there will be any thread issues (unless there are any assumptions in AWT/Swing code about there only being one thread).
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Event handler

Hi...
I would like to know about event handler txn code: "crmv_event"
Can any one educate me about this ? How is this functionality used.?
Any example ?
Regards,
sanjana

hi sanjana
CRMV_EVENT t code is used to establish the vents from background
since you are a functional consultant you must know that for any action to trigger in foreground there must be an event which actually triggers the event
there are many events to establish that event ,this is just one of the way
here using the calling options you can sopecify that whatever event you are trying to establish ,you are doing it for what application
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to say in functional lingo the event which we have just created using the t code can be used to trigger the action in appliocation in which we have tried to call that event
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this way we decides the timings of the actions in the background of which we have created that event
hope i clear ur doubt
best regards
ashish

Migration from Serial polling to Serial queue with event handler

Hi, I am trying to migrate from classical serial polling communications to serial queue with "event handler" for the buttons pressed by the user. I have placed four while loops, one for the event handler, a second one for serial reading, a third one for serial writing (depending on what button was pressed) and the last one for processing what was read from the serial reading while loop, via a queue.
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First of all, only once just after running the LV program, I must turn on my attached device with an ON command plus a carriage return after that the device will respond with the number of sensors plugged to it, disabling the corresponding buttons in the front panel. Then labview must wait until I pressed Acquire Button (event handler) and send a CF command plus what sensors to acquire plus a carriage return, then the device will respond continuously to labview with the sensor readings until I press the stop button (event handler), there is also another button to exit the program, also with event handler.
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Take a look at my VI and you will soon notice what kind of problems I am having, any suggestions will welcome.
Thank's in advance.
Regards.
Attachments:
serial queue.zip ‏76 KB

Hi Luisete,
Maybe the problem arise because you are En- and DeQueue in parallel. You do a lot of things in parallel, that is nice if you are sure that one loop doesn't have to wait for another loop. Make sure you don't dequeue before enqueue.
Hope this helps
I never knew that the standard error cluster output could be wired directly to the loop control of a while loop.
First time I see this

Event handling using CAN?

I am aware of how to make LabView respond to user interface events (keyboard presses, button presses, mouse moves, etc) and I'm also aware that the same event handling structure can be used to handle external (non-GUI) events- like those generated by a digital edge on a DAQmx input. My question is whether the same event handling structure can be used to handle external events coming in on a CAN network- via NI-CAN or otherwise?
Is there a good reference which summarizes ALL general types of events that can be handled in this way- not just the standard GUI events? I have a feeling that ActiveX and VISA are other ways to generate events, but can't find a good resource in general - or specifics on the NI-CAN side.
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Thanks Mike- still not sure I understand. What should I wire to the Create User Event block in order for available events to show up in the dialog which allows me to configure events in a given frame? For example, I have an external micro-controller communicating with LabVIEW using a CAN network. Usually the communication is started by LabVIEW and sends commands out- but I also want to be able to handle asynchronous messages generated by this micro-controller in an event fashion without having do any polling. Is there some reference I can wire to the Create User Event block which will make an event like "Incoming CAN Network Traffic" available to be handled in an event structure?
Thanks again!

Event handling with JSF

Hi Everybody,
I have a question about event handling and I am just wondering if I can do the following with JSF.
I have two HTML dropdown lists A and B. When ever a value changes in list A, based on the selected value, list B has to be populated. Is it possible to do with JSF? Can you guys give me pointers where some code samples may be available?
Cheers!
Krish

Take a look at the JSF Value-Changed Listener sections

Use event handler programmatically

Hello, I use the Labview 8.2.1 and I would like to ask something about event handler.
I have some buttons and I use an event handler to perform their tasks. The buttons are used only with the mouse and not programmatically.
Now, I want to use a button programmatically without pressing it. I didn't find how to do this, so I created a boolean variable and I added to the event handler of a button a second "Event Specifier" of that boolean variable with the event "value change".
I assumed that it would work, but it does not, that is, the event handler is not used when the value of the boolean variable changes.
How can I solve it?
Thank you in advance.
Solved!
Go to Solution.

Write to the Value(Sgnl) property node of the variable you want to change. This will set off an event programatically.
- tbob
Inventor of the WORM Global

Question on program structure about event handling in nested JPanels in GUI

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