I have a thread which enables and disables a button in certain random time, if the button clicked when it is enabled an action performed will be executed which will change the image of the button. I am concerned about the synchronization here. Suppose the button is about to get disable and got clicked, so now both threads will execute one to disable it and other to change the image. How should I synchronize this?
All Java GUI toolkits (be it Swing, Apache Pivot, JavaFX, AWT, SWT, Android...) are single-threaded. This means that all listeners will always fire in the same thread. So:
no, you don't need to perform any kind of synchronization,
yes, you need to take care so that disabling and enabling the button happens in the gui thread (wahetever it's called). The exact code is toolkit-specific.
Related
I have some JTextComponents with some CaretEvents. I need to disable all the components to prevent user interaction after a certain actions and when that actions are completed reenable those JTextComponents to allow the user to interact again with the GUI. Obviously when the user clicks on a JTextComponent the caret listener performs it's actions and I want to prevent that.
I currently removed the CaretListeners to prevent that and after my internal operations are completed I re-add those CaretListeners.
Is there any other way to prevent that? Such removing the MouseEvents for those components and reassign that later?
One way to disable user interaction is to not allow the text component to receive the program's focus:
myTextComponent.setFocusable(false);
And then later when you want to re-allow interaction, make the same call with the obvious true parameter:
myTextComponent.setFocusable(true);
I'm working on a Java project involving user interface, using the Button class and some action listeners.
I have a few buttons (each with an action listener) and I want to add a timeout to the whole program. That means, if no button was clicked-on in a certain amount of time, a specific action should be performed.
I tried adding it among the basic while loop + isDisposed() function. To my knowledge, this loop checks multiple times whether a button was clicked-on. For some reason, I couldn't get the outcome I wanted.
Is there a way to do so with the classes I mentioned? I also couldn't find any suitable functions in the Button class.
Use a Swing Timer (javax.swing.Timer).
Instanciate it with new Timer(CERTAIN_AMOUNT_OF_TIME, e -> timeoutAction()) (If you have a function timeoutAction), disable repeating with setRepeats(false) and start() it.
When the user clicks a button, call restart() on it.
Also, you’re mentioning the Button class, which is an AWT class. I recommend using Swing’s JButton class instead.
It is highly probable that you are using swing, but since this is not specified, I will give you a general answer, with links to swing examples.
First of all, since all your button clicks will behave in a very similar manner, so you will need a custom ActionListener (example). Your custom action listener should perform the action, but set a timestamp or some kind of date value to the current moment. In parallel, you should have a heartbeat event, which periodically (frequently) runs and compares the current moment with the timestamp set by the last button click. And you can see an example of a periodic task here: How to schedule a periodic task in Java?
I'd like to update GUI elements (JComboBox, JLabel, etc.) from code which shouldn't trigger change event. Is it possible to find out from java.awt.event.ActionEvent or java.awt.event.ItemEvent if the change was caused by an user or by running code like this?
combo.setSelectedItem("my item")
The answer is: no.
But in some cases you can try to analyze the current InputEvent. To get it, use EventQueue.getCurrentEvent(). For example if user has triggered the change on clicking of another component, you can compare the component of the input event and the component of the action event (OK I know: it's unsafe. But in some cases it can help to avoid incrementing of application complexity).
For a button you can get the event modifiers:
int buttonModifiers = evt.getModifiers();
If the button event was generated with a call to doClick() the modifier is 0, otherwise not.
By the way, you can find out such differences relatively easy by logging / printing using evt.toString()
.
I have a simple program that utilizes Java Swing Timer to display an image for 400 miliseconds, in this period of time I just want to stop all ActionListeners or stop taking ActionEvents. I've got 40+ buttons and want a simple way to do this.
Is there anyway to do that in Java?
Can you determine that you are in this "image displayed" state? The image goes up and you set the state to "image displayed" or whatever. Go through your widgets and decide which ones are supposed to be dead while the image is up. Turn them into Observers of this state value. When the state changes, they either enable or disable, as appropriate. The image code doesn't do anything directly to any widget. It just declares that the state is now "image displayed". It's up to the Observers to decide what to do, if anything, with that information.
Or use the GlassPane. That works too. Of course, the GlassPane shuts down everything. If you need to be more selective, you need a more fine-tuned approach.
You can use a temporary GlassPane instance to consume all events by registering empty listeners to it.
Use an undecorated modal JDialog to display the image. Before you make the dialog visible you would start a Timer. When the Timer fires in 400 ms you close the dialog.
I've had similar issues and typically found that its a design issue that got me in that situation. Being the case, I still had to find away around it. To fix the issue, I kept a list of the elements that I wanted to disable (stop listening) and iterated through them at the beginning and end of the timer. For buttons it should be as simple as:
for(Component c : listOfToggledComponents){
c.setEnabled(shouldItBeEnabled);
}
For buttons, this will grey out the button. Similar things happen to other swing components.
I'm using the java swing library to develop a board game called DAO.
The problem is that after the human player makes its move, by clicking on the JButton with the piece image that he wants to play, I call the computer AI routine but inside the mouse event function. By doing this only when the function returns, the computer ends its turn, do the JButtons refresh their Images (setIcon comes in).
I'd like to know how can I force the JButtons to change their image at the moment they are clicked and not only when the mouse event function ends (as I need to handle data inside it).
I've tried all of this
myButtons[i][j].setIcon(xIcon);
myButtons[i][j].revalidate();
myButtons[i][j].repaint();
myButtons[i][j].validate();
None worked.
Thx in advance
You may want to try putting the action performed upon clicking the JButton into a Swing worker. This will allow the task to go on in the background, while the user can still click other buttons, etc.
See http://java.sun.com/docs/books/tutorial/uiswing/concurrency/simple.html.
There is a single thread used for all Swing activity.
Here's the process.
One event appears on the event queue
it is pulled from the queue and executed by The AWT Thread
Any new events created while this is executing are placed on the queue to be held until the currently running AWT event returns.
The event executing returns and the next event on the queue is dequeued and executed.
This means that if you need to do anything that takes more than, say 1/100 of a second or so, you shouldn't do it any thread started from a swing event. Instead, spawn your own thread and return the swing thread to the system so the GUI can be updated.
Now, your thread MUST NOT update any GUI objects! If you need to update a GUI object, use invokeLater to place your code back on the AWT thread.
New Java programmers not conforming to this rule and executing tasks on the AWT thread is almost certainly the biggest reason people think Java is slow.