Develop Reference

Can I call ActionPerformed method from an Event Handler class for JButton?

I have a JButton titled "select"
In the class that creates that JButton and other classes, I want to use an if condition with ActionPerformed method.
Something like(pseudo-code)
if(_selectListener.actionPerformed(ActionEvent)) { //i.e., if select Button is clicked,
//do something
}
Is this possible?
I want to call this method because I have to handle a situation in which a player should be able to choose something by clicking "select" button, or another "scroll" button, and I want to control it using something similar to a bunch of if statements like the one above.
If it is possible, what is the syntax for it? What is the argument ActionEvent?
Thank you!

The easiest and cleanest way is to add a dedicated, specific action listener to each button. That way, when the actionPerformed() method is called, you're sure that the associated button has been clicked, and don't need to test which button has been clicked:
selectButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// handle click on select button
}
});
scrollButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// handle click on scroll button
}
});
Another way is to use a common ActionListener, and use the getSource() method of ActionEvent to know which component triggered the event. Compare the result with each potential button to determine which is the one that has been clicked:
#Override
public void actionPerformed(ActionEvent e) {
if (e.getSource() == selectButton) {
// handle click on select button
}
else if (e.getSource() == scrollButton) {
// handle click on scroll button
}
}
What is the argument ActionEvent?
The answer is in the documentation. Read it.

no you cant call, if needs boolean expression/value, but this method returns void.

Java Swing: Focus issue

I'm making a level editor for my game. I have a property panel where I can modify the selected object its properties. I also have a Save button to write the level xml.
A field-edit is submitted(*) when the editor component lost the focus or Enter is pressed. This is working great, but the only problem is that when I have this sequence of actions:
Edit a field
Press the save button
Because, what happens is this:
I edit the field
I press the save button
The level is saved
The field lost the focus
The edit is submitted
As you can see, this is the wrong order. Of course I want the field to lose its focus, which causes the submit and then save the level.
Is there a trick, hack or workaround to make the field first lose the focus and then perform the action listener of the save button?
Thanks in advance.
(* submit = the edit to the field is also made in the object property)
EDIT: For the field I'm using a FocusAdapter with focusLost:
FocusAdapter focusAdapter = new FocusAdapter()
{
#Override
public void focusLost(FocusEvent e)
{
compProperties.setProperty(i, getColor());
record(); // For undo-redo mechanism
}
};
And for the button a simple ActionListener with actionPerformed`.
btnSave.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
// Save the level
}
});

Hmm ... can't reproduce: in the snippet below the lost is always notified before the actionPerfomed, independent on whether I click the button or use the mnemonic:
final JTextField field = new JTextField("some text to change");
FocusAdapter focus = new FocusAdapter() {
#Override
public void focusLost(FocusEvent e) {
LOG.info("lost: " + field.getText());
}
};
field.addFocusListener(focus);
Action save = new AbstractAction("save") {
#Override
public void actionPerformed(ActionEvent e) {
LOG.info("save: " + field.getText());
}
};
save.putValue(Action.MNEMONIC_KEY, KeyEvent.VK_S);
JButton button = new JButton(save);
JComponent box = Box.createHorizontalBox();
box.add(field);
box.add(button);
On the other hand, focus is a tricky property to rely on, the ordering might be system-dependent (mine is win vista). Check how the snippet behave on yours.
If you see the same sequence as I do, the problem is somewhere else
if you get the save before the lost, try to wrap the the save action into invokeLater (which puts it at the end of the EventQueue, so it's executed after all pending events)
Action save = new AbstractAction("save") {
#Override
public void actionPerformed(ActionEvent e) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
LOG.info("save: " + field.getText());
}
});
}
};

Normally, wrapping your save code into an SwingUtilities.invokeLater() should do the trick. As you already mentioned, this doesn't work? Try this:
private boolean editFocus = false;
FocusAdapter focusAdapter = new FocusAdapter()
{
#Override
public void focusGained(FocusEvent e){
editFocus = true;
}
#Override
public void focusLost(FocusEvent e){
compProperties.setProperty(i, getColor());
record(); // For undo-redo mechanism
editFocus = false;
if (saveRequested){
save();
}
}
};
and for your button:
private boolean saveRequested = false;
btnSave.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
if (editFocus){
saveRequested = true;
return;
} else {
save();
}
}
});
and then your save method:
private void save(){
// do your saving work
saveRequested = false;
}
This only works when your focusLost gets called after your button's action. If suddenly the order is correct, this code will get save() called twice.
But again, wrapping your save() code in your original approach should work, because the save code will execute after processing all events. That is after processing your button click and your focusLost events. Because your focusLost code executes immediately (it's not wrapped in an invokeLater()), the focusLost code should be executed always before your save code. This does not mean that the event order will be correct! But the code associated to the events will executed in the right order.

How to make JComboBox selected item not changed when scrolling through its popuplist using keyboard

I have a JComboBox component in the panel and ItemListener attached to it. But it gets fired after every up/down keypress (when scrolling though opened popup list). I want to change the selected value after the user accepts selection by pressing for example Enter key.
This is not a case when using mouse. When I move mouse over the combobox's list the highlight follows mouse pointer, but selected item is not changed until I press the mouse button. I would like to have the same behavior for keyboard, i.e. moving highlight via up/down arrow does not change selected item, but pressing Enter does.

I believe you should be able to do:
comboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);
after you have created your comboBox instance to get this functionality

In Java 8 they have fixed this behaviour, but only trigger if u set one UI property
UIManager.getLookAndFeelDefaults().put("ComboBox.noActionOnKeyNavigation", true);

the JComboBox.isTableCellEditor method works for arrow movement through the list, but does not work for type-ahead supported by the KeySelectionManager. i.e. you still get ActionEvents for every non-navigation key the user types, as the JComboBox interprets those characters for searching though the model to move to (or move close to) the user's intended selection.
this solution has a drawback in that it changes the action command for mouse clicks, which was a OK compromise for me because the the flow of the GUI forces the user to change the focus away from the combo box
I ended up making a special KeyListener, that relys on changing the combo box's default action command from comboBoxChanged to comboBoxMovement. Here's the line of code I need after my combo box is all initialized:
setExplicitSelectionManager(myComboBox);
... and here is the method and its contained class that do all the work:
private void setExplicitSelectionManager(JComboBox comboBox) {
class ExplicitSelectionManager implements KeyListener, FocusListener {
private JComboBox src;
private KeyListener superKeyListener;
ExplicitSelectionManager(JComboBox src) {
this.src = src;
// we like what the default key listener does, but not the action command
// it uses for ActionEvents it fires for plain text type-ahead characters
this.superKeyListener = src.getKeyListeners()[0]; // we only have one
src.removeKeyListener(superKeyListener); // will be replace right away, below
}
#Override
public void keyTyped(KeyEvent e) {
// basic combo box has no code in keyTyped
}
#Override
public void keyPressed(KeyEvent e) {
// in the default JComboBox implementation, the KeySelectionManager is
// called from keyPressed. I'm fine with the implementation of
// the default, but I don't want it firing ActionEvents that will cause
// model updates
src.setActionCommand("comboBoxMovement");
this.superKeyListener.keyPressed(e);
src.setActionCommand("comboBoxChanged");
if (e.getKeyCode() == 10) {
src.setSelectedIndex(src.getSelectedIndex());
}
}
#Override
public void keyReleased(KeyEvent e) {
// basic combo box has no code in keyReleased
}
#Override
public void focusGained(FocusEvent e) {
}
#Override
// this will also give us the event we want, if the user decides to Tab out of
// the combo box, instead of hitting Enter
public void focusLost(FocusEvent e) {
src.setSelectedIndex(src.getSelectedIndex());
}
}
ExplicitSelectionManager newSelectionManager = new ExplicitSelectionManager(comboBox);
comboBox.addKeyListener(newSelectionManager);
comboBox.addFocusListener(newSelectionManager);
}
... and here's the action performed method
private void comboBoxActionPerformed(java.awt.event.ActionEvent evt) {
JComboBox source = (JComboBox) evt.getSource();
// "comboBoxChanged" is the default,
// so any normal JComboBox can also use this action listener
if (evt.getActionCommand().equals("comboBoxChanged")) {
updateModel(source.getName(), (String) source.getSelectedItem());
}
}

Its the expected behavior with the ItemListener. whenever the displayed value changes the event is fired. For your requirement use an ActionListener.

JComboBox actions

Is there a way to distinguish between a JComboBox's index being changed programatically using setSelectedBoundValue and by clicking on the JComboBox?

This is ugly and truly a hack, but works!
The ActionEvent contains a field modifiers which in this case is the mouse button id. So using that may help you distinguish between setSelectedIndex or setSelectedValue and mouse clicks (by the way setSelectedBoundValue is not a method on JComboBox):
box.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (e.getModifiers() != 0) {
// ~ mouse button pressed ;)
}
}
});

setSelectedBoundValue
Never heard of that method?
Is there a way to distinguish between a JComboBox's index being changed programatically
Not really. You can remove the listener:
comboBox.removeActionListener(...);
comboBox.setSelectedItem(...);
comboBox.addActionListener(...);
You can set your own class variable.
manualSelection = true;
comboBox.setSelectedIndex(...);
manualSelection = false;

Mouse events on an SWT Scrollbar

Using standalone SWT Scrollbars is something of a hack (using this workaround), but it can be done. Here's a snippet:
ScrolledComposite scrolledComposite = new ScrolledComposite(
parent, SWT.V_SCROLL);
ScrollBar scrollbar = scrolledComposite.getVerticalBar();
Shell tip = new Shell(UserInterface.getShell(), SWT.ON_TOP
| SWT.NO_FOCUS | SWT.TOOL);
// ..stylize and fill the tooltip..
Now what I'm trying to do is monitor when the user is interacting with the scrollbar. In particular, I want to know when the user is dragging the scrollbar—and when it has been released—in order to display an Office 2007-style tooltip revealing which page the position of the scrollbar corresponds with.
Presently, I have the following code which displays the tooltip:
scrollbar.addSelectionListener(new SelectionListener() {
public void widgetDefaultSelected(SelectionEvent event) {}
public void widgetSelected(SelectionEvent event) {
tip.setVisible(true);
}
}
It would seem logical then to have the tooltip disappear when the mouse button is released:
scrollbar.addListener(SWT.MouseUp, new Listener() {
public void handleEvent(Event event) {
tip.setVisible(false);
}
});
However, neither scrollbar nor scrolledComposite seem to respond to the SWT.MouseUp event when the user interacts with the scrollbar.
I presently have a workaround that hides the tip after a timeout, but I'm not satisfied with this. Any insights would be most appreciated!

Scrollbar's javadoc said this:
When widgetSelected is called, the
event object detail field contains one
of the following values: SWT.NONE -
for the end of a drag. SWT.DRAG.
SWT.HOME. SWT.END. SWT.ARROW_DOWN.
SWT.ARROW_UP. SWT.PAGE_DOWN.
SWT.PAGE_UP. widgetDefaultSelected is
not called.
So my suggestion is get your tooltip to appear and disappear is to check for the event.detail type.
public void widgetSelected(SelectionEvent event) {
tip.setVisible(event.detail != SWT.NONE);
}

scrollBar.addSelectionListener(new SelectionListener() {
public void widgetDefaultSelected(SelectionEvent e) {
}
public void widgetSelected(SelectionEvent e) {
if (e.detail == SWT.NONE) {
// end of drag
System.out.println("Drag end");
}
else if (e.detail == SWT.DRAG) {
// drag
System.out.println("Currently dragging");
}
}
});
Hope this will help you... But I can see a problem with mousewheel use that throws multiple drag end events...

Paul,
try using addMouseEvent method from a Scrollable object. For example:
Scrollable scrollable = scrollbar.getParent();
scrollable.addMouseListener(new MouseListener () {
void mouseDoubleClick(MouseEvent e) { ... }
void mouseDown(MouseEvent e) { ... }
void mouseUp(MouseEvent e) { ... }
});
Actually, I don't know if this approach will work. But, it's an attempt.
Good luck!