I've built a form with Netbeans's visual editor. When I press one of the buttons it should do the following :
set it to disabled
perform a task that takes some time
when the task finishes the button will be enabled again
However, the following happens:
the button remains in a pressed state until the task finishes
when the task finishes, the enabling/disabling of buttons will be very fast (they will happen, but you won't notice them)
This behaviour is not something I want. I tried using repaint on the JButton, on the JFrame and even on the JPanel containing the button, but I can't seem to get it to do what I want. Some hints?
When you do work in a button callback, you are stalling the GUI painting thread until it completes.
What you need to do is spawn a thread to do the long running task, and then have that thread use SwingUtilities.invokeLater() to update the UI when it completes. Not using invokeLater is not thread safe, and is generally bad mojo.
A basic example is:
button.setEnabled(false);
new Thread(new Runnable() {
public void run() {
// Do heavy lifting here
SwingUtilies.invokeLater(new Runnable() {
public void run() {
button.setEnabled(true);
}
});
}
}).start();
When you do things in a button callback, you are essentially stalling the gui painting thread - not just for the button, but for ANY gui painting. (Try covering the interface with another window and then exposing it again - it won't repaint until the task is finished!)
What you need to do is spawn a thread to do the long running task, and then have that thread use SwingUtilities.invokeLater() to do the enabling of the button. invokeLater forces the button enable to happen in the gui painting thread.
You may want to set a busy cursor or otherwise lock the interface while the long-running thread is operating.
The Concurrency in Swing tutorial from Sun is well worth a read. Excellent explanation and background reading, including the event dispatching thread, using worker threads, etc
You need to do the task that takes some time in a different thread.
The reason the button is blocking is because the work is being done in the same thread that draws the button. Once the work is done the button can do the rest of what you tell it to.
If you use a different thread the thread will go do the task while the drawing code can continue drawing the form.
Related
just a question about SwingUtilities.InvokeLater().
To my understanding, any time I update my Swing interface I need to call SwingUtilities.InvokeLater to get onto the EDT. Does this need to be done if I am attempting to update my GUI from a button listener, as they button events are already on the EDT?
i.e, would i have to..
public void mouseClicked(MouseEvent e) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
//GUI updates
}
});
}
or would I simply be able to...
public void mouseClicked(MouseEvent e) {
//GUI updates
}
Furthermore, Does the same logic apply if I am calling a method on an object that will update the GUI?
any time I update my Swing interface I need to call SwingUtilities.InvokeLater to get onto the EDT
Correct. This includes any time you update the model of the component, since this will also result in the repainting of the component.
Does this need to be done if I am attempting to update my GUI from a button listener, as they button events are already on the EDT?
Again correct. Since the code is automatically invoked on the EDT you do not need to manually add it to the EDT using the invokeLater().
You typically use the SwingUtilities.invokeLater() if your code is executing on a separate Thread and part of that logic needs to update a GUI component.
Updating this message :
Swing event handling code runs on a special thread known as the event dispatch thread. So all of the component(button, checkbox, radio button etc.,) actions are handled on EDT. So no need to have SwingUtilities.invokeLater() inside your button action as it always runs on EDT.
Tasks on the event dispatch thread must finish quickly; if they don't, unhandled events back up and the user interface becomes unresponsive.
So if you are planning to perform a long running task that could affect a GUI inside an action then better go for Worker Threads or Background Threads.
SwingWorker has doInBackground(), done() and process() methods to handle the long running tasks well without impacting the GUI.
Go through below links to get more info
Why does SwingUtilities.invokeLater() cause JButton to freeze?
What does SwingUtilities.invokeLater do?
https://www.javacodegeeks.com/2012/12/multi-threading-in-java-swing-with-swingworker.html
I'm creating a board game using a GUI and JFrames/JPanels where you can play against the computer. I have a method called showPieces() which updates board GUI by changing the image icons on an array of buttons (which are laid out in a grid format). Once the icons have been updated the revalidate() and repaint() methods to update the GUI.
The showPieces() method has a parameter that needs to be passed to it every time it is called.
The main issue I'm having is I want the human to make a move, update the GUI, wait 1 second, the computer makes it's move and then loop until someone wins.
My basic code is the following:
do{
human.makeMove();
gui.showPieces(data);
try {
Thread.sleep(1000);
} catch(InterruptedException ex) {
Thread.currentThread().interrupt();
}
computer.makeMove()
gui.showPieces(data);
}while(playing);
This cause the issue where when the human player makes their move, the GUI will freeze for one second and then after the delay, both moves are made at the same time.
I hope it makes sense, but I'm a novice with Java and may have to look more into threading as I don't understand it well enough.
Thread.sleep() is done on the Event Dispatch Thread which will lock the GUI.
So If you need to wait for a specific amount of time, don't sleep in the event dispatch thread. Instead, use a timer.
int delay = 1000; //milliseconds
ActionListener taskPerformer = new ActionListener() {
public void actionPerformed(ActionEvent evt) {
//...Perform a task...
}
};
new Timer(delay, taskPerformer).start();
As with most all similar Swing questions, you're putting your entire Swing GUI to sleep by calling Thread.sleep(...) on the GUI's event thread (the EDT or Event Dispatch Thread), and when during this period the GUI will not be able to update its images or interact with the user whatsoever. The solution here is not to use Thread.sleep(...) but rather to use a Swing Timer to cause your 1 second delay.
Swing Timer Tutorial.
I have the following Java Code which adds a JRadioButton to a JPanel and handles its mouse click event
JRadioButton offline = new JRadioButton();
offline.setText("Offline Mode");
modePanel.add(offline);
modePanel.setLayout(new GridLayout(2,1));
offline.addMouseListener(new java.awt.event.MouseAdapter() {
public void mouseClicked(java.awt.event.MouseEvent evt) {
offlineClicked(evt);
}
});
The function offlineClicked takes roughly around 1 min to be executed completely.
And until its execution is completed no other actions performed are handled.
All actions performed thereafter seem to go to a Eventqueue and handled FIFO when the offlineClicked has completed execution.
Due to this the UI seems to have gone into a hung state.
What can be done to make swing handle events concurrently and not wait till the last is executed completely.
When the mouselistener event is fired it runs on the event dispatch Thread (the swing gui thead that redraws the screen). If you put logic code in the gui thread then your gui would freeze until the logic completes and returns the gui thread back to swing. You can use swingworker or another option is to simply start a new thread and let the gui thread return so it can let other gui events process. In the new thread do your time consuming logic, it's running off of the event loop so swing won't freeze as it's running async. You MUST run all swing code on the dispatch thread so when the logic is done since you are no longer on the dispatch thread you have to add it to the event queue.
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
// you can now safely use swing components
new frame.setVisible(true);
}
} );
i need to develop java code to have JFrame with a text filed and button.Using Threads,i need to update time for every one minute in the title bar of JFrame.Using Another Thread i need to display textbox value in the console when a button is clicked.I have code for performing both operations (updating time for every min and getting text box value)but i dont know how to add two threads in same class.if anyone knows pls help me out
What you are asking is a dangerous thing to do in Swing. Swing components are not thread-safe and should only be updated from the Event Dispatching Thread (also known as the EDT or Swing Thread). To do this, Swing has utility methods such as SwingUtilities.invokeLater(Runnable) which will execute the code in the Runnable (at some point in the future) on the EDT. The idea is that you place your code to do Swing-things (like update the Title of the JFrame with the time) inside of a separate Runnable and pass it to invokeLater().
To do this, you can create an anonymous Runnable class:
Runnable updateJFrame = new Runnable () {
public void run () {
myJFrame.setTitle("My New Title");
}
};
SwingUtilities.invokeLater(updateJFrame);
Using invokeLater() also ensures that the components get refreshed/repainted properly after they have been updated. (The behavior you are seeing when using statics may actually be a refresh/repaint issue.) The moral of this story is that if you manipulate Swing components on a non-EDT thread, all bets are off.
In a method of a class, I update the same label twice. The first time, it shows the user message to wait, but the second time shows the user the completed message. Something like the following:
MyClass{
myMethod(){
jLabel.setText("Please wait...");
//does calculation
jLabel.setText("Completed successfully!");
}
}
When I run the app, all I see is the "Completed successfully" message. Is the JLabel updating too quickly? How do I control it? I tried using the following but no luck :(
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
jLabel.setText("Please wait...");
}
});
If the calculation is done in the event dispatch thread, then it blocks the thread and prevents it from doing all its repaintings. You must do the computation in another thread, and have this thread change the label text when it ends (in the event dispatch thread, using SwingUtilities.invokeLater, or by using the SwingWorker mechanism). If the computation is really fast, it's not worth it, though, because the second text will appear so quickly after the first one that you won't even notice the first one.
Have a look at SwingWorker, which is designed for such use-cases. Its javadoc contains a useful example.
if you want to delay some Action/Event then use javax.swing.Timer, or wrap your code to the Runnable#Thread,
notice: never use Thread.sleep(int) durring EDT, your GUI freeze until Thread.sleep(int) ended
example for javax.swing.Timer & Runnable#Thread & Freeze GUI by implements Thread.sleep(int) durring EDT here
Possibly because your calculations are happening too fast. Did you try putting a delay after your calc.
Also as Nizet points out above if this is happening in EDT the component will not repaint until end of the thread which means it will take the last set value.