I'm building a user-interface with Java's swing library, and I've run into a problem.
When updating a text-area in a long method, there is a pause while the method runs, and then the text area is updated all at once, instead of a little bit at a time.
I managed to fix the problem using a new thread in the following manner:
private void jButtonActionPerformed(java.awt.event.ActionEvent evt) {
Thread x = new Thread() {public void run() {
// do things that update a text area
}}; x.start();
}
This works perfectly for having the text area update in small pieces, as opposed to all at once.
However, the only problem is that this method can only be called once or Java crashes. I read that this has to do with only being able to create the thread one time. How can I modify the code to keep the desired functionality?
Any help would be greatly appreciated.
Well, I doubt you codes crashing because of the Thread creation, because each time the method is called, you're creating a new Thread (you can't restart an existing instance of a Thread that has already been started (even if it's completed or not)), the likely cause is you're getting a concurrent modification exception because Swing is not Thread safe...
Probably the easiest solution would be to use a SwingWorker which will allow you to execute your long running task in the background, but provide easy to use functionality to update the UI safely, through the publish, process and done methods.
Do prevent possible issues, you might also consider disabling the button until the load action is completed, which will prevent people from mashing the button spawning multiple background processes...
Well you can make new object of the Thread and override all the method means runnable.
new Thread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
System.out.println("Executed..*****");
}
}).start();
try this.
Just for comparison's sake, here is an example using SwingUtilities.invokeLater. I echo MadProgrammer's advice though, learning about SwingWorker is much more beneficial in the long term and gives better variable handling.
newGame.addActionListener(new ActionListener() {
#Override
public void actionPerformed(final ActionEvent arg0) {
panelList.get("newGame").setEnabled(false);
SwingUtilities.invokeLater(new Runnable() {
public void run() {
// this is where the heavy processing occurs
newGameButton();
// re-enables the button afterwards
panelList.get("newGame").setEnabled(true);
}
});
}
});
Also, once your code is working better, you can probably look into ways to optimise the speed of the update (even when dealing with Swing objects). The above call used to hang for a second or so, but I've got the delay to about 50 - 100ms or so with further work on the model :)
Related
I'm refactoring some code that runs a multi-stage process. Each step is inside a nested java.awt.EventQueue.invokeLAter.... call. It looks a little like this:
import java.awt.EventQueue;
public class NestedInvokeLater {
/**
* #param args
*/
public static void main(String[] args) {
java.awt.EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
changeTabPanel();
copySomeFiles();
enableNextButton1();
upDateProgressBar(10);
java.awt.EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
readInFiles();
doSomethingToFiles();
upDateProgressBar(15);
java.awt.EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
doSomethingElse();
upDateProgressBar(100);
}
});
}
});
}
});
};
}
I am new enough at Java that I don't get the point of nesting these calls to add 'jobs' to the EDT, and I'm not 100% confident with fiddling with these calls either. I think I understand what the invokeLater call does, and what each step does. Please correct me if this understanding is wrong:
invokeLater is used to add some invocation to the list of jobs to be done in the Event Dispatch thread. Java then deals with when/how each invocation is done, ensuring that the EDT and in turn the GUI doesn't lock as it performs jobs 'in the background'.
Nesting these calls says to me that we should queue a set of jobs, one of which is to queue something, which will queue some jobs....one of which is to queue something. But the first inner invocation is only ever queued once the previous job is done. Everything occurs sequentially (this is in line of my understanding of the whole process), but I don't see why you would use nested requests to queue jobs to do so. I would have, if I was writing this from scratch, have simply created functions for each invocation and called them in turn.
I recognise, being only a novice at Java I am probably missing something huge that makes this nesting important. But there is no documentation of this, and no commenting in the code about the nesting.
What am I missing? What, if anything is the point in this code?
There is no point in doing so many nested invocations. It is based on a good intention, but it's badly implemented.
If you want to do this properly, use a SwingWorker.
The documentation of SwingWorker has a neat example of how you should implement performing several tasks in the background of the application (the PrimeNumbersTask class showed there).
Edit: Here's an example of what you should do with SwingWorker in your case.
class SequentialInvoker extends SwingWorker<Void, Integer> {
#Override
public void doInBackground() {
changeTabPanel();
copySomeFiles();
enableNextButton1();
setProgress(10);
readInFiles();
doSomethingToFiles();
setProgress(15);
doSomethingElse();
setProgress(100);
}
}
To actually show the progress on a progress bar, take a look at the following code, copied from the SwingWorker documentation:
JTextArea textArea = new JTextArea();
JProgressBar progressBar = new JProgressBar(0, 100);
SequentialInvoker task = new SequentialInvoker();
task.addPropertyChangeListener(
new PropertyChangeListener() {
public void propertyChange(PropertyChangeEvent evt) {
if ("progress".equals(evt.getPropertyName())) {
progressBar.setValue((Integer)evt.getNewValue());
}
}
});
With this code, your progress bar will show the progress as the SwingWorker works.
One advantage of doing it this way is that other queued up things get to run in between. So, in between the section that does changeTabPanel() and the part that does readInFiles(), the GUI will get to respond to the user clicking on a button etc...
The actual implementation is a bit of a confusing mess and illustrates (IMHO) why anonymous functions were not such a good idea. Your inclination to make the three parts "real" functions and call them sequentially is a good one. But, to maintain the same logic, what you really need to do is make them three runnables and have each invokeLater the subsequent one.
And #Cyrille is correct that doing these major tasks on the EDT is poor practice.
There are three jobs that are used in invokeLater here. Each one does a costly thing, call updateProgressBar and then adds the next job to the EDT.
The thing is, if the code just continued to the next costly thing instead of calling invokeLater to do it, the EDT would not have the chance to repaint the progress bar to show the new value of it. This is probably why the work is broken in three invokelater calls.
Now, this is not what I would call a good code. This is pretty bad practice: one should not do a long process in the EDT because it blocks everything and makes the GUI unresponsive. This should be changed so that the process is done in a separate thread, and then only call invokeLater to update the progress bar.
Edit: To answer more generally the question in the title: there is almost never a sensible reason to nest calls to invokeLater. When you are doing this, you say "queue this job so that it is done in the same thread but later when you feel it would be good". So it gives a chance to the rest of the GUI to repaint itself, like here. But it only makes sense if you have a long running process in the EDT, which you should always avoid.
The code you posted makes absolutely no sense to me - you can just write everything sequentially because you have no parallel threads running which might post events on the EDT. You need the first invokeLater() though, as you use Swing components.
But as your code suggests you are doing some relatively lengthy operations: reading files, do something with them, ... You should run these methods in a new worker thread, NOT the EDT. And, in the run() method of these worker threads, you'll need a call to EventQueue.invokeLater() to have your GUI updated.
I am trying to create a program to perform a simple task and produce an output every x seconds. I also want the program to run until I decide to manually close the program.
I have been attempting to implement this using a Swing timer, as I believe this is the best way. The problem is I'm not sure how to keep the program going once the main method has finished executing. So for example I have:
static ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
try {
//do stuff
} catch (Exception e) {
e.printStackTrace();
}
}
};
public static void main(String[] args) throws Exception{
Timer timer = new Timer(3000, taskPerformer);
timer.start();
}
which just finishes execution immediately. I can dodge the problem by putting the current thread of execution to sleep Thread.currentThread().sleep(..), but this feels like a botch job, and will be ultimately be finite in duration. I can also do while(true), but I believe this is bad practice.
My question is how to get the desired persistence behavior, and if there is a better way than using Swing timers.
Thanks.
A Swing Timer will stay alive as long as the EDT is alive, usually this is done by having a Swing GUI present and visible (this creates a non-daemon thread that persists until the GUI exits). If you don't need a Swing GUI, then don't use a Swing Timer. Perhaps instead use a java.util.Timer, and don't exit the main method til you give the word (however you plan to do that).
Use java.util.Timer instead. The associated thread will not run as a daemon.
There is actually more than 1 question.
Given Model View and Controller. (Mine are coupled a lot - View knows its Controller, and Controller knows View.)
Does new threads in Controller can be fired in basic manner - with the new Runnable(){ (...) run(){}} or it is required to do in some "swing way", to make it properly? Maybe with Timer or invokeLater()?
Second thing is - assuming that new thread has started - when it operates directly on view, setting some JTextFields (and so on) - do methods such as setThatTextFieldWithNewValue(msg) need to be synchronized as a result of being called from need thread? If so - is there any better approach that gives less coupling and less spend time thinking about needed synchronization?
there are a few ways how is possible to create, manage and notify MVC, for better help sooner post an SSCCE
Runnable#Thread is very confortable, stable and clear way, but I'd suggest to wrap all output to the Swing GUI into invokeLater, including thread safe methods as setText, append e.g. are ..
as Kumar Vivek Mitra (+1) metioned there is SwingWorker, but required deepest knowledge about Java essential classes, some trouble are there with exceptions recycle how to get exception from SwingWorker
about MVC maybe will help you my similair question
Swing is not Thread-Safe
1. The UI thread is the Event Dispatcher Thread, which is responsible for the Gui work.
2. Try working with Non-Ui threads outside the UI thread.
3. Yes offcourse you can fire a thread from within the UI thread, but its advisable to keep it out of
the UI thread, else the GUI may seems non-responsive.
(ie. the Non-UI work on the Non-UI thread OUT of the UI thread which is responsible for the UI Work)
4. Well there is a swing way too... use SwingWorker, this handles the synchronization between UI and Non-UI thread.
Edited part:
// PLEASE NOTE ITS NOT GOOD TO ADD COMPONENTS DIRECTLY ON THE FRAME/JFRAME, BUT I AM DOING THIS JUST TO SHOW, WHAT I MEANT.
public class MyClass extends JFrame{
private final JButton b;
public MyClass(){
this.setSize(300,300);
this.setComponent();
this.setHandler();
}
public void setComponent(){
b = new JButton("Click");
this.add(b);
}
public void setHandler(){
b.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
// Do whatever you want...
}
});
}
public static void main (String[] args) {
EventQueue.invokeLater(new Runnable(){ // UI THREAD
public void run(){
MyClass s = new MyClass();
s.setVisible(true);
}
});
}
}
Main method is short lived in Swing, The main method() schedules the Construction of GUI to the Event Dispatcher Thread (EDT), and then quits. So its EDT responsibility to handle the GUI. So its always advisable to keep the Non-UI work on the Non-UI thread away from EDT.
Anything in swing has to run on the EventQueue. If you have a method called from swing it will already be running there (as in an Action listener). If you don't know if you're on the event queue, EventQueue.isDispatchThread() will tell you. When you know you're not, reference a swing class or method using EventQueue.invokeLater() or invokeAndWait if you need to see results. (This must be done from the main method.)
Be very careful about this; you have to check your code. If not, my experience is that the swing UI will be just a little bit flakey, with the occasional unreproducable oddity. There's no easy way around eyeballing each line of code.
Actually, there is. Do everything on the EventQueue, then you won't have to worry. You're probably not doing a whole lot of work outside swing anyway. If you are, it's probably worth the loss of speed to avoid multithreading problems. If your non-swing work is extensive but simple, use the SwingWorker class. It gives you an extra thread under highly controlled conditions and should save you a lot of grief.
Your classes (View and Controller) are independent of threads, and should work just fine all running in one thread. Don't confuse classes and threads. (I'll admit, I'd be tempted to have the Controller firing off threads in all directions, but you have to be prepared to be very careful and know everything there is to know about multithreading.)
If you do multithread, the EventQueue can be a bit handy because you don't have to protect fields referenced only there--it's an island of single threading in a dangerous sea. On the other hand, don't do any synchronization there; you'll block your UI. You can launch threads from there and you may have to just to avoid blocking. (Once you start multithreading, it's hard to stop.)
The easiest way would be:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
// Run your code here.
}
});
For more complex tasks (send process chunks to ui thread, respond to jobFinished):
new SwingWorker<String, String>() {
#Override
protected void done() {
}
#Override
protected void process(List<String> arg0) {
}
#Override
protected String doInBackground() throws Exception {
}
}.execute();
I have an animation in which triggers an event. This event fires a lot of computing usage and thus stutters the UI.
What I need to do is keep the thread running smoothly. When the event happens it will pass a string down to the thread, perform calculations (including using the audioRecord class) and return a boolean variable.
I have looked around and it seems AsyncTask may be the best solution, but I wanted to see if any of you had any ideas? Considering performance, Is this the best way to go?
Thanks,
Ben
Generally AsyncTask is fine.
But if you dont need to acess the UI thread for your background operation you can simply use a new thread.
new Thread(new Runnable() {
public void run() {
//do stuff
}
}).start();
I know that using threads is more efficient than using c# DoEvents(), but I was still wondering whether there is an equivalent function in java. I googled for it, but I couldn't find anything.
You can use Thread.yield(), which is the java counterpart to relinquish the control of the processors voluntarily.
You can use EventQueue.invokeLater() to append a Runnable after all pending events. This have a result similar to C#'s DoEvents() that comes before the code you put inside the Runnable.run() method.
See Java documentation for EventQueue.
For example, if you want to let all GUI controls to lose the focus and their lost focus events to be execute, you can use the following code:
#Override
public void windowClosing(WindowEvent e){
// Clear the focus to allow last changes to be noted.
KeyboardFocusManager.getCurrentKeyboardFocusManager().clearGlobalFocusOwner();
// We want to let other events (e.g. lost focus) run before we start closing.
EventQueue.invokeLater( new Runnable() {
#Override public void run() {
// Do actual closing...
}
});
}