I have two basic questions.
I have a GUI project with Java Swing. When I put buttons on the frame and I double clicked them, I had the code of the actionPerformed, but it is blocked.
How can I put there a button and then use it on a actionListener?
My Project is about Server-client (multithread and sockets)
I call one method to reiceve one string that we can write on a JtextField and it stays on a while cicle with PrintWriter and a getOutputStream.
Something like:
do{
...
}while(thisstring!=null || thisstring!="exit")
So.. when I write something and press the button to send it, it stays on the cicle and the button blocks. How can I unblock the button to write something else?
Edit:
I understood the EDT problem, but I can't solve it.
I tried use the Timer but without success, something like that:
int delay = 1000; //milliseconds
ActionListener listener = new ActionListener() {
public void actionPerformed(ActionEvent e) {
//My action calling the Thread class with the while cicle that has the PrintWriter
}
};
new Timer(delay, listener).start();
How can I handle this to do the timer when I press the button?
How can I stay on the that cicle (read the comment line) to send the information by OutputStream every time that one user enter something on the text field?
I know that for example for a console application I use a BufferedReader and then I use the ReadLine() to wait for anything sent from the console, but with GUI interface it freezes all time..
There is a fundamental concept in Java GUI development surrounding which thread in which the developer implements user-interaction processing such as button clicks.
In short, you need to perform your processing outside of the thread that calls your action handling method. This single thread is known as the Event Dispatch Thread (EDT), and if you have logic that runs much more than a few milliseconds, it will prevent the UI from continuing to draw things like the button releasing, etc.
You'll want to move your long-running, socket code off the EDT. Doing so will allow the button to release and let the user interact with other controls (or even the same button).
To avoid duplicating other discussions on the topic, I direct you to this pretty good one. Additionally, this article gives a short overview of threading concepts in Swing.
Regards,
ScottH
According to your comment you have some naming issues there. You need a class that implements the ActionListener-interface like so: class YourListenerClass implements ActionListener, but you could also do that via an anonymous class like new ActionListener {
public void actionPerformed(ActionEvent e) {
//your code for your button here
}
});
when you set your ActionListener.
The crucial thing is that you need to name your method the correct way. It MUST be public void actionPerformed(ActionEvent e) and you definitely have to implement the ActionListener-interface.
The next thing is that you have to register your listener in your button like:
yourButton.addActionListener(new YourListenerClass);
or
insert an anonymous class like I showed to you before.
The 2nd thing sounds like an multithreading issue like I mentioned in my comment. I didnt follow scotth's link, but according to his description this might be a source you want to read to solve any further blocking issues.
EDIT:
Well, at first I didn't want to explain it, because it's quite a chunk of code, but as the problem persists I want to add something about SwingWorkers in my answer.
If you have long running code, it wont help to use a Timer as the code invoked by it will also be on the EDT as it's triggered by an event.
Instead of that you could use a SwingWorker to solve this. This needs some extra code, though.
Here's a simple approach you could follow:
public class WorkingHard{
SwingWorker<String, String> worker;
JButton yourButton = ...;
...
//do some cool stuff, as register those listeners!
...
public void actionPerformed(ActionEvent evt){
if(evt.getSource().equals(yourButton);
// Construct a new SwingWorker
worker = new SwingWorker<String, Void>(){
#Override
protected String doInBackground(){
//do your reading in this method, it will be executed in an own thread
String readText = "i will be read".
/*your reading algorithm, you could also call publish(...) to post your results,
e.g. likewise), then you also have to override process(...). this process will be
thread save, too*/
readText += ... ;
...
return readText;
}
#Override
protected void done(){
try {
//do sth. with your result, now thread safe.
someGuiElement.setText(get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
};
// Execute the SwingWorker; the GUI will not freeze
worker.execute();
}
}
If you want to know more about those workers... there several threads dealing about it, e.g. this one.
Related
I'm making a small game and I've already implemented a save function in which the game is saved (by writing information to a new XML file). The saving takes a couple of seconds and I want to do the following: while the program is saving the game, I want to change the look of the JPanel, and when it is done saving, I want to go back to another page(show another JPanel).
I have the following code:
confirm.addActionListener(new ActionListener () {
#Override
public void actionPerformed(ActionEvent e){
String fileNaam = saveGame.getText();
//This method changes the look of the panel
changePanel();
//This method saves the game
model.saveGame(fileNaam);
//This method takes the user back to a previous page
controller.viewTeamPage();
}
});
What happens is that the game is saved and the user is taken back to the teampage, but the panel is never changed. The changePanel() method does work, so that is not the problem but it seems like it is never executed. I was wondering if somebody knows how I can fix this.
EDIT:
private void changePanel () {
panel.removeAll();
panel.repaint();
panel.revalidate();
}
This is the method to change the look of the panel, for now I just remove everything on the panel to keep it simple.
Also, the saving is not done in a separate Thread, is that something I should look at?
EDIT 2: I fixed it by using a thread to save the game and return to the teampage after the saving is done. See the code below.
confirm.addActionListener(new ActionListener () {
#Override
public void actionPerformed(ActionEvent e){
final String fileNaam = saveGame.getText();
changePanel();
Thread t = new Thread (new Runnable () {
#Override
public void run() {
model.saveGame(fileNaam);
controller.viewTeamPage();
}
});
t.start();
}
});
If you are changing the same panel and not intializing a new panel then the problem i think is that you need to call the panel.revalidate or panel.repaint i think. I made a demo for a Procedural generation project and i had to do this to make my panel change.
Call your save game method from a new thread but don't "join" or "try" to wait for this thread to finish from inside the method actionPerformed();
Make the call to controller.viewTeamPage() after the save game thread is done saving the game. One simple way of doing that would be passing the "controller" object to the constructor of your custom thread so you can make that call after saving the game.
The step 1 is very important in this case because all the calls you are making in the method actionPerformed() are being made in the UI thread, preventing the entire UI from refreshing until the method returns. Even calling repaint() alone, in changePanel(), wont be enough because it just "schedules" a refresh on you panel that will only happen after actionPerformed() returns. If you put the most time consuming call in a separate thread however, the actionPerformed() returns quickly allowing the UI to be refreshed while the game saving thread is doing its job.
To expound a little more, I have a GUI that looks like:
Then I have an action listener on the OK button that starts like:
//OK Button Action Listener
private void okButtonActionPerformed(ActionEvent e) {
//Enable/Disable Buttons
okButton.setEnabled(false);
cancelButton.setEnabled(true);
updateCheckbox.setEnabled(false);
//Move on to a series of other methods here...
Which should, in theory, make this happen:
However, instead, I get the following until ALL methods and other things connected to the OK button are completed:
This obviously can't happen, because the idea is to make the cancel button available and the OK button and several other tick-boxes unavailable for the duration of the program (Image 2), where, instead, it freezes in a half-state (Image 3). Is there any way to combat this?
Every time you execute logic from the GUI you should be using the SwingWorker in the following way:
SwingWorker myWorker= new SwingWorker<String, Void>() {
#Override
protected String doInBackground() throws Exception {
//Execute your logic
return null;
}
};
myWorker.execute();
If you want to update the GUI from inside this logic use InvokeLater:
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
//To update your GUI
}
});
With this you can be sure that both your logic and your GUI stay responsive.
Edit:
You could also use invokeAndWait if this suits your needs more. Link to related answer
//Move on to a series of other methods here...
Make sure you don't block the GUI thread (EDT) with long-running operations. Instead use SwingWorker.
Are you doing some processing on the same thread that's handling the GUI? You might want to look into a SwingWorker thread to do the heavy stuffin the background so your UI remains responsive if so.
Yup, that's because you have blocked with EDT with your other methods.
You need to use another Thread to do the work in the background otherwise the GUI will be blocked.
In Swing applications it is recommended that any long running tasks are carried out on a SwingWorker.
Take a look at the documentation for an introduction.
A SwingWorker will carry out a task that it is given and it can report back to the GUI when it is done. This will be done in a non-blocking way so that you can still use the GUI while the task it being carried out.
If you want to be able to cancel the background task you need to keep a reference to the SwingWorker so that you can call the cancel method. In this case the work method needs to be interruptable, otherwise the task cannot be cancelled.
I've been attempting to write a server program for a game and one issue that I am experiencing is writing to my 'log' (which is just a JTextArea's caption) from another class/thread. Basically, the setup is this:
MainWindow:
-JTextArea with the log.
Threads are started from MainWindow. They may need to output something, and basically what I am after is instead of printing whatever these threads need to output to System.out I can print them to my log, in my MainWindow (which is a JFrame). Is there a way to access the MainWindow from the threads? I don't really know how else to explain this.
Thanks
SwingUtilities.invokeLater() is made for that purpose.
final String labelText = "current label text";
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
// Write your GUI updater code here
// like this
labelOnTheGui.setText(labelText);
}
});
This is the only way you can manipulate the GUI starting the action from a different thread.
I have a Blackjack game that I've made in Java and I want to signal the start of the game by clicking a button. All my action listeners work just fine and all that, but the problem lies in that I can't figure out how to start the game without it running completely within the actionPerformed method. Obviously, a function continuously running within the actionPerformed method will effectively disable the rest of my GUI. Here's a code snippet....
go.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
// START GAME SOMEHOW but must run outside of action listener
}
});
Obviously, a function continuously running within the actionPerformed method will effectively disable the rest of my GUI.
This is a valid observation and shows that you have understand the fundamental rule when working with Swing.
Your game is most likely event driven (correct me if I'm wrong) so the action performed by the button should just set the program in a new state, waiting for further events. This is nothing that should be time consuming, and is typically done directly by the EDT.
Of course, if you want to do a fancy start-new-game animation, that needs to be performed in a separate thread, in which case you simply start the animation thread (I would recommend using a SwingWorker though) from within the actionPerformed method, and then return.
In code, I imagine it would look something like this:
go.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// Remove the menu components
someJPanel.removeAll();
// Show the game table
someJPanel.add(new GamePanel());
someJPanel.revalidate();
someJPanel.repaint();
// done. Wait for further user actions.
}
});
You game should probably start in its own thread and manage that itself (hard to say), but to get you going you could start your game in a new "external" thread, something like this in your actionPerformed:
public void actionPerformed(ActionEvent e) {
Thread thread = new Thread("Game thread") {
public void run() {
startGame(); //or however you start your game
}
};
thread.start();
}
I believe that you want to extend javax.swing.SwingWorker.
The non-ui start-up functionality would run in doInBackground and the done method would be called when it finishes to update the ui.
There's even an example in the javadoc Class Description to update a progressbar with the status of what's happening in start-up.
Since I'm not a CS major, I'm having some difficulties translating my programming wishes into an actual program.
What it basically boils down to is the following: how can I alternate an image on a label, showing each image for an amount of tim specific for each image.
So: say I've images A and B; I'd like the user to see A for 1000ms and B for 200ms. This keeps on looping until a user presses a certain key.
Now, I'm able to load an image onto a panel, quite easily even, and I've managed to catch user input using KeyListener and stuff, which all works quite nicely and alot easier then I had expected. I also know how to use looping constructs like while, for and do..while, but this timer business is shady.
I see all kinds of stuff using threads and what not, I really don't need that. This is not about efficient programming or good code, it's simply about demonstrating something.
Any help would be greatly appreciated!
Use a SwingWorker<Void, Void>. The doInBackground method of the SwingWorker should look like this :
#Override
protected Void doInBackground() {
try {
while (true) {
displayImage(imageA);
Thread.sleep(1000L);
if (isCancelled()) {
return null;
}
displayImage(imageB);
Thread.sleep(200L);
if (isCancelled()) {
return null;
}
}
}
catch (InterruptedException e) {
// ignore
}
return null;
}
private void displayImage(final Icon image) {
SwingUtilituies.invokeLater(new Runnable() {
#Override
public void run() {
// display the image in the panel
}
});
}
The keylistener should simply cancel the SwingWorker.
Here's something that might be a good example:
http://www.java2s.com/Code/Java/Development-Class/UsejavautilTimertoscheduleatasktoexecuteonce5secondshavepassed.htm
I can try to explain the code if it appears confusing
There is nothing necessarily inefficient about using threads when threads are the right tool for the job.
In this case, it would not be unreasonable to create a new class that implements Runnable, which holds a reference to the label you wish to change the image on.
This means that the image could be changed without causing waits on the main application that would cause it to hang until it was done.
You would want to avoid 'Busy Loops' [basically, a while loop with no Thread.sleep() within it], and look to see if there is any needed thread exit criteria