Assume we have the following Swing application:
final JFrame frame = new JFrame();
final JPanel outer = new JPanel();
frame.add(outer);
JComponent inner = new SomeSpecialComponent();
outer.add(inner);
So in this example we simply have an outer panel in the frame and a special component in the panel. This special component must do something when it is hidden and shown. But the problem is that setVisible() is called on the outer panel and not on the special component. So I can't override the setVisible method in the special component and I also can't use a component listener on it. I could register the listener on the parent component but what if the outer panel is also in another panel and this outer outer panel is hidden?
Is there an easier solution than recursively adding component listeners to all parent components to detect a visibility change in SomeSpecialComponent?
Thanks aioobe for your answer - I got here via Google, looking for the same thing. :-) It's worth noting that Component.isShowing() does the same job as your amIVisible() though, so a revised code snippet (including a check on the nature of the HierarchyEvent) might be:
class SomeSpecialComponent extends JComponent implements HierarchyListener {
public void addNotify() {
super.addNotify();
addHierarchyListener(this);
}
public void removeNotify() {
removeHierarchyListener(this);
super.removeNotify();
}
public void hierarchyChanged(HierarchyEvent e) {
if ((e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) != 0)
System.out.println("Am I visible? " + isShowing());
}
}
To listen for this kind of events occuring in the hierarchy, you could do the following.
class SomeSpecialComponent extends JComponent implements HierarchyListener {
private boolean amIVisible() {
Container c = getParent();
while (c != null)
if (!c.isVisible())
return false;
else
c = c.getParent();
return true;
}
public void addNotify() {
super.addNotify();
addHierarchyListener(this);
}
public void removeNotify() {
removeHierarchyListener(this);
super.removeNotify();
}
public void hierarchyChanged(HierarchyEvent e) {
System.out.println("Am I visible? " + amIVisible());
}
}
You could even be more precise in the treatement of HierarchyEvents. Have a look at
http://java.sun.com/javase/6/docs/api/java/awt/event/HierarchyEvent.html
Have a look at the ComponentListener (or ComponentAdapter)
http://java.sun.com/docs/books/tutorial/uiswing/events/componentlistener.html
http://docs.oracle.com/javase/8/docs/api/java/awt/event/ComponentListener.html
And specifically the method:
void componentHidden(ComponentEvent e)
Invoked when the component has been made invisible.
A complete solution would look something like:
inner.addComponentListener(new ComponentAdapter() {
public void componentHidden(ComponentEvent ce) {
System.out.println("Component hidden!");
}
});
If the actions that should be carried out upon hiding is tightly coupled with the SomeSpecialCompnent, I would suggest to let SomeSpecialComponent implement ComponentListener, and add itself as a listener for the ComponentEvents in its constructor.
Another useful way (more related to add/remove operations and perhaps not suitable for your specific scenario) is to override addNotify() and removeNotify().
Related
I realize this is a repeat question, but my circumstances are a little bit different. I need to have a MouseListener in another class that can altar the background color of the object that calls it. Please help me.
public class LeftListPanel extends JPanel {
public LeftListPanel() {
setBackground(Settings.BACKGROUND_COLOR);
setLayout(null);
addPersonalStatsTab();
}
private void addPersonalStatsTab() {
JPanel personalStatsPanel = new JPanel();
personalStatsPanel.addMouseListener(new CustomMouseListener());
JLabel personalStatsText = new JLabel("Text");
personalStatsPanel.add(personalStatsText);
add(personalStatsPanel);
}
Then I have an inner-nested class for the MouseListener because this is the only place this MouseListener will be called.
class CustomMouseListener implements MouseListener {
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
setBackground(Settings.BACKGROUND_COLOR.brighter());
}
#Override
public void mouseExited(MouseEvent e) {
setBackground(Settings.BACKGROUND_COLOR);
}
}
The setBackground(COLOR) lines are those who don't work... this.setBack and super.setBack ARE NOT working in this case.. I'M DESPERATE FOR HELP!
The reason you don't see the background changes is that when you call setBackground, you are de-referring (implicitly) the this object, i.e. the instance of LeftListPanel. So, you are actually changing its background, but you don't see it because inside the LeftListPanel instance there is another JPanel (instantiated at the addPersonalStatsTab method) which occupies the whole visible space (or even it is not visible at all, because of that weird null layout; I don't know exactly).
Fist of all, I recommend to you not to set null as a layout. Chose a proper layout, or let it be defaulted - do not call setLayout(null).
Then, set personalStatsPanel as a private member of LeftListPanel. And when calling to setBackground, use it as the scope reference:
LeftListPanel.this.personalStatsPanel.setBackground(...);
This works, I instead just created a private method where I pass in the panel I want to apply it too.
private void CustomMouseListener(JPanel panel) {
panel.addMouseListener(new MouseAdapter() {
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
panel.setBackground(Settings.BACKGROUND_COLOR.brighter());
}
#Override
public void mouseExited(MouseEvent e) {
panel.setBackground(Settings.BACKGROUND_COLOR);
}
});
}
Thank you all for your time and suggestions :)
You could...
Pass a reference of the component you want changed to the CustomMouseListener
class CustomMouseListener implements MouseListener {
private JPanel panel;
public CustomMouseListener(JPanel panel) {
this.panel = panel;
}
#Override
public void mouseReleased(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
panel.setBackground(Settings.BACKGROUND_COLOR.brighter());
}
#Override
public void mouseExited(MouseEvent e) {
panel.setBackground(Settings.BACKGROUND_COLOR);
}
}
This is okay if you want to use the listener on a limited number of components, but if you want to use the same listener on a number of components...
You could...
Use the source property of the MouseEvent to get which component triggered the event
#Override
public void mouseEntered(MouseEvent e) {
if (!(e.getSource() instanceof JPanel)) {
return;
}
JPanel panel = (JPanel)e.getSource();
panel.setBackground(Settings.BACKGROUND_COLOR.brighter());
}
or, a better solution would be to do something more like...
#Override
public void mouseEntered(MouseEvent e) {
e.getComponent().setBackground(Settings.BACKGROUND_COLOR.brighter());
}
since the information is already provided to you (just not, this returns an instance of Component, so if you need to access the Swing specific properties, you'd still need to cast it).
Why is this approach better?
CustomMouseListener listener = new CustomMouseListener();
panel1.addMouseListener(listener);
panel2.addMouseListener(listener);
panel3.addMouseListener(listener);
panel4.addMouseListener(listener);
panel5.addMouseListener(listener);
panel6.addMouseListener(listener);
panel7.addMouseListener(listener);
because it's agnostic, meaning you can create a single instance of the listener and re-use on multiple components
I'm trying to implement a KeyListener for my JFrame. On the constructor, I'm using this code:
System.out.println("test");
addKeyListener(new KeyListener() {
public void keyPressed(KeyEvent e) { System.out.println( "tester"); }
public void keyReleased(KeyEvent e) { System.out.println("2test2"); }
public void keyTyped(KeyEvent e) { System.out.println("3test3"); }
});
When I run it, the test message comes up in my console. However, when I press a key, I don't get any of the other messages, as if the KeyListener was not even there.
I was thinking that it could be because the focus is not on the JFrame
and so they KeyListener doesn't receive any events. But, I'm pretty sure it is.
Is there something that I am missing?
If you don't want to register a listener on every component,
you could add your own KeyEventDispatcher to the KeyboardFocusManager:
public class MyFrame extends JFrame {
private class MyDispatcher implements KeyEventDispatcher {
#Override
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getID() == KeyEvent.KEY_PRESSED) {
System.out.println("tester");
} else if (e.getID() == KeyEvent.KEY_RELEASED) {
System.out.println("2test2");
} else if (e.getID() == KeyEvent.KEY_TYPED) {
System.out.println("3test3");
}
return false;
}
}
public MyFrame() {
add(new JTextField());
System.out.println("test");
KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
manager.addKeyEventDispatcher(new MyDispatcher());
}
public static void main(String[] args) {
MyFrame f = new MyFrame();
f.pack();
f.setVisible(true);
}
}
You must add your keyListener to every component that you need. Only the component with the focus will send these events. For instance, if you have only one TextBox in your JFrame, that TextBox has the focus. So you must add a KeyListener to this component as well.
The process is the same:
myComponent.addKeyListener(new KeyListener ...);
Note: Some components aren't focusable like JLabel.
For setting them to focusable you need to:
myComponent.setFocusable(true);
InputMaps and ActionMaps were designed to capture the key events for the component, it and all of its sub-components, or the entire window. This is controlled through the parameter in JComponent.getInputMap(). See How to Use Key Bindings for documentation.
The beauty of this design is that one can pick and choose which key strokes are important to monitor and have different actions fired based on those key strokes.
This code will call dispose() on a JFrame when the escape key is hit anywhere in the window. JFrame doesn't derive from JComponent so you have to use another component in the JFrame to create the key binding. The content pane might be such a component.
InputMap inputMap;
ActionMap actionMap;
AbstractAction action;
JComponent component;
inputMap = component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
actionMap = component.getActionMap();
action = new AbstractAction()
{
#Override
public void actionPerformed(ActionEvent e)
{
dispose();
}
};
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0), "dispose");
actionMap.put("dispose", action);
I got the same problem until i read that the real problem is about FOCUS the your JFrame has already added Listeners but tour frame is never on Focus because you got a lot of components inside your JFrame that also are focusable so try:
JFrame.setFocusable(true);
Good Luck
KeyListener is low level and applies only to a single component. Despite attempts to make it more usable JFrame creates a number of component components, the most obvious being the content pane. JComboBox UI is also often implemented in a similar manner.
It's worth noting the mouse events work in a strange way slightly different to key events.
For details on what you should do, see my answer on Application wide keyboard shortcut - Java Swing.
Deion (and anyone else asking a similar question), you could use Peter's code above but instead of printing to standard output, you test for the key code PRESSED, RELEASED, or TYPED.
#Override
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getID() == KeyEvent.KEY_PRESSED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
} else if (e.getID() == KeyEvent.KEY_RELEASED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
} else if (e.getID() == KeyEvent.KEY_TYPED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
}
return false;
}
in order to capture key events of ALL text fields in a JFrame,
one can employ a key event post processor.
Here is a working example, after you add the obvious includes.
public class KeyListenerF1Demo extends JFrame implements KeyEventPostProcessor {
public static final long serialVersionUID = 1L;
public KeyListenerF1Demo() {
setTitle(getClass().getName());
// Define two labels and two text fields all in a row.
setLayout(new FlowLayout());
JLabel label1 = new JLabel("Text1");
label1.setName("Label1");
add(label1);
JTextField text1 = new JTextField(10);
text1.setName("Text1");
add(text1);
JLabel label2 = new JLabel("Text2");
label2.setName("Label2");
add(label2);
JTextField text2 = new JTextField(10);
text2.setName("Text2");
add(text2);
// Register a key event post processor.
KeyboardFocusManager.getCurrentKeyboardFocusManager()
.addKeyEventPostProcessor(this);
}
public static void main(String[] args) {
JFrame f = new KeyListenerF1Demo();
f.setName("MyFrame");
f.pack();
f.setVisible(true);
}
#Override
public boolean postProcessKeyEvent(KeyEvent ke) {
// Check for function key F1 pressed.
if (ke.getID() == KeyEvent.KEY_PRESSED
&& ke.getKeyCode() == KeyEvent.VK_F1) {
// Get top level ancestor of focused element.
Component c = ke.getComponent();
while (null != c.getParent())
c = c.getParent();
// Output some help.
System.out.println("Help for " + c.getName() + "."
+ ke.getComponent().getName());
// Tell keyboard focus manager that event has been fully handled.
return true;
}
// Let keyboard focus manager handle the event further.
return false;
}
}
This should help
yourJFrame.setFocusable(true);
yourJFrame.addKeyListener(new java.awt.event.KeyAdapter() {
#Override
public void keyTyped(KeyEvent e) {
System.out.println("you typed a key");
}
#Override
public void keyPressed(KeyEvent e) {
System.out.println("you pressed a key");
}
#Override
public void keyReleased(KeyEvent e) {
System.out.println("you released a key");
}
});
Hmm.. what class is your constructor for? Probably some class extending JFrame? The window focus should be at the window, of course but I don't think that's the problem.
I expanded your code, tried to run it and it worked - the key presses resulted as print output. (run with Ubuntu through Eclipse):
public class MyFrame extends JFrame {
public MyFrame() {
System.out.println("test");
addKeyListener(new KeyListener() {
public void keyPressed(KeyEvent e) {
System.out.println("tester");
}
public void keyReleased(KeyEvent e) {
System.out.println("2test2");
}
public void keyTyped(KeyEvent e) {
System.out.println("3test3");
}
});
}
public static void main(String[] args) {
MyFrame f = new MyFrame();
f.pack();
f.setVisible(true);
}
}
I have been having the same problem. I followed Bruno's advice to you and found that adding a KeyListener just to the "first" button in the JFrame (ie, on the top left) did the trick. But I agree with you it is kind of an unsettling solution. So I fiddled around and discovered a neater way to fix it. Just add the line
myChildOfJFrame.requestFocusInWindow();
to your main method, after you've created your instance of your subclass of JFrame and set it visible.
lol .... all you have to do is make sure that
addKeyListener(this);
is placed correctly in your code.
You could have custom JComponents set their parent JFrame focusable.
Just add a constructor and pass in the JFrame. Then make a call to setFocusable() in paintComponent.
This way the JFrame will always receive KeyEvents regardless of whether other components are pressed.
I currently have an abstract class which extends JComponent. In this class I have defined a method as follows:
public void makeMouseOverListener(){
System.out.println("Inside make mouseover...");
MouseMotionListener ret = new MouseMotionListener(){
public void mouseDragged(MouseEvent e) {
}
public void mouseMoved(MouseEvent e) {
System.out.println("Mouse Moved");
}
};
this.addMouseMotionListener(ret);
}
I extend this abstract class with a few other objects, and in the constructors of each of those objects I call this method. I always see the first println, but the "Mouse Moved" line never shows up in my console. I also tried directly creating this MouseMotionListener in each constructor, but with the same results. So ultimately my question is, How can I ensure that I get a working motion listener into my objects? Thank you in advance!
The code inside of the new MouseMotionListener( code ) it seems like this ..
**
MouseMotionListener ret = new MouseMotionListener(
public void mouseDragged(MouseEvent e) {
}
public void mouseMoved(MouseEvent e) {
System.out.println("Mouse Moved");
}
});
**
If you're invoking makeMouseOverListener in the constructor of your custom components, then its very likely that the mouse position is never positioned over the component itself. Ensure that the dimension of the component is great than 0 x 0. This can be achieved by using a layout manager. e.g. position the component at BorderLayout.CENTER location.
I need help to understand the event propagation in Swing. I know that each event is handled by only one component. Thus, when I have a panel outside with some child panel inside and I add mouseListeners to both of them, the one of inside will be called. That's nice and that's the expected behavior.
But I don't understand the behavior in the following situation:
inside registers a MouseMotionListener and outside registers a MouseListener. I expect inside to consume all MouseMotionEvents and outside to receive the MouseEvents, because there is no listener for normal MouseEvents on inside. But that's not the case, inside somehow consumes all MouseEvents not only the MouseMotionEvents.
The following code illustrates the problem:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class EventTest {
public static void main(String... args) {
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
JComponent inside = new JPanel();
inside.setBackground(Color.red);
inside.setPreferredSize(new Dimension(200,200));
MouseMotionListener mm = new MouseMotionListener() {
#Override
public void mouseDragged(MouseEvent arg0) {
System.err.println("dragged");
}
#Override
public void mouseMoved(MouseEvent arg0) {
System.err.println("moved");
}
};
// next line disables handling of mouse clicked events in outside
inside.addMouseMotionListener(mm);
JComponent outside = new JPanel();
outside.add(inside);
outside.setPreferredSize(new Dimension(300,300));
outside.addMouseListener( new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
System.err.println("clicked");
}
});
JFrame frame = new JFrame();
frame.add(outside);
frame.pack();
frame.setVisible(true);
}
});
}
}
I could work around the problem by registering a listeners on inside for all events the parent component might be interested in and then calling dispatchEvent to forward the event to the parent.
a) can someone point me to some docs, where this behavior is described? The javadocs of MouseEvent made me think that my expectations were right. So, I need a different description to understand it.
b) is there a better solution than the one sketched above?
Thanks,
Kathrin
Edit: It is still unclear, why Swing behaves this way. But as it looks, the only way to get the stuff working is to manually forward the events, I will do it.
a) By design, Java mouse events "bubble up" only if there in no mouse listener on the child component.
b) You can forward events to another component, as shown here and below.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class EventTest {
public static void main(String... args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
final JComponent outside = new JPanel();
JComponent inside = new JPanel();
inside.setBackground(Color.red);
inside.setPreferredSize(new Dimension(200, 200));
inside.addMouseMotionListener(new MouseAdapter() {
#Override
public void mouseDragged(MouseEvent e) {
System.err.println("dragged");
}
#Override
public void mouseMoved(MouseEvent e) {
System.err.println("moved inside");
outside.dispatchEvent(e);
}
});
outside.add(inside);
outside.setPreferredSize(new Dimension(300, 300));
outside.addMouseMotionListener(new MouseAdapter() {
#Override
public void mouseMoved(MouseEvent arg0) {
System.err.println("moved outside");
}
});
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.add(outside);
frame.pack();
frame.setVisible(true);
}
});
}
}
Very similar to trashgod's answer - you can use a MouseAdapter as your motion listener, and override it to forward any events you want to be handled by the parent. This should only add a minimal amount to your code.
MouseAdapter mm = new MouseAdapter() {
#Override
public void mouseDragged(MouseEvent arg0) {
System.err.println("dragged");
}
#Override
public void mouseMoved(MouseEvent arg0) {
System.err.println("moved");
}
#Override
public void mouseClicked(MouseEvent e) {
outside.dispatchEvent(e);
}
};
// For forwarding events
inside.addMouseListener(mm);
// For consuming events you care about
inside.addMouseMotionListener(mm);
I too couldn't find any way around using the dispatchEvent(e) method. I think you're stuck with that route.
This worked out for me:
Ellipse2D mCircle = new Ellipse2D.Double(x,y,size,size);
void PassMouseEvent(MouseEvent e) {
getParent().dispatchEvent(e);
}
public void mousePressed(MouseEvent arg0) {
if(mCircle.contains(arg0.getX(), arg0.getY())) {
// Do stuff if we click on this object
} else {
// Pass to the underlying object to deal with the mouse event
PassMouseEvent(arg0);
}
}
I'm trying to implement a KeyListener for my JFrame. On the constructor, I'm using this code:
System.out.println("test");
addKeyListener(new KeyListener() {
public void keyPressed(KeyEvent e) { System.out.println( "tester"); }
public void keyReleased(KeyEvent e) { System.out.println("2test2"); }
public void keyTyped(KeyEvent e) { System.out.println("3test3"); }
});
When I run it, the test message comes up in my console. However, when I press a key, I don't get any of the other messages, as if the KeyListener was not even there.
I was thinking that it could be because the focus is not on the JFrame
and so they KeyListener doesn't receive any events. But, I'm pretty sure it is.
Is there something that I am missing?
If you don't want to register a listener on every component,
you could add your own KeyEventDispatcher to the KeyboardFocusManager:
public class MyFrame extends JFrame {
private class MyDispatcher implements KeyEventDispatcher {
#Override
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getID() == KeyEvent.KEY_PRESSED) {
System.out.println("tester");
} else if (e.getID() == KeyEvent.KEY_RELEASED) {
System.out.println("2test2");
} else if (e.getID() == KeyEvent.KEY_TYPED) {
System.out.println("3test3");
}
return false;
}
}
public MyFrame() {
add(new JTextField());
System.out.println("test");
KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
manager.addKeyEventDispatcher(new MyDispatcher());
}
public static void main(String[] args) {
MyFrame f = new MyFrame();
f.pack();
f.setVisible(true);
}
}
You must add your keyListener to every component that you need. Only the component with the focus will send these events. For instance, if you have only one TextBox in your JFrame, that TextBox has the focus. So you must add a KeyListener to this component as well.
The process is the same:
myComponent.addKeyListener(new KeyListener ...);
Note: Some components aren't focusable like JLabel.
For setting them to focusable you need to:
myComponent.setFocusable(true);
InputMaps and ActionMaps were designed to capture the key events for the component, it and all of its sub-components, or the entire window. This is controlled through the parameter in JComponent.getInputMap(). See How to Use Key Bindings for documentation.
The beauty of this design is that one can pick and choose which key strokes are important to monitor and have different actions fired based on those key strokes.
This code will call dispose() on a JFrame when the escape key is hit anywhere in the window. JFrame doesn't derive from JComponent so you have to use another component in the JFrame to create the key binding. The content pane might be such a component.
InputMap inputMap;
ActionMap actionMap;
AbstractAction action;
JComponent component;
inputMap = component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
actionMap = component.getActionMap();
action = new AbstractAction()
{
#Override
public void actionPerformed(ActionEvent e)
{
dispose();
}
};
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0), "dispose");
actionMap.put("dispose", action);
I got the same problem until i read that the real problem is about FOCUS the your JFrame has already added Listeners but tour frame is never on Focus because you got a lot of components inside your JFrame that also are focusable so try:
JFrame.setFocusable(true);
Good Luck
KeyListener is low level and applies only to a single component. Despite attempts to make it more usable JFrame creates a number of component components, the most obvious being the content pane. JComboBox UI is also often implemented in a similar manner.
It's worth noting the mouse events work in a strange way slightly different to key events.
For details on what you should do, see my answer on Application wide keyboard shortcut - Java Swing.
Deion (and anyone else asking a similar question), you could use Peter's code above but instead of printing to standard output, you test for the key code PRESSED, RELEASED, or TYPED.
#Override
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getID() == KeyEvent.KEY_PRESSED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
} else if (e.getID() == KeyEvent.KEY_RELEASED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
} else if (e.getID() == KeyEvent.KEY_TYPED) {
if (e.getKeyCode() == KeyEvent.VK_F4) {
dispose();
}
}
return false;
}
in order to capture key events of ALL text fields in a JFrame,
one can employ a key event post processor.
Here is a working example, after you add the obvious includes.
public class KeyListenerF1Demo extends JFrame implements KeyEventPostProcessor {
public static final long serialVersionUID = 1L;
public KeyListenerF1Demo() {
setTitle(getClass().getName());
// Define two labels and two text fields all in a row.
setLayout(new FlowLayout());
JLabel label1 = new JLabel("Text1");
label1.setName("Label1");
add(label1);
JTextField text1 = new JTextField(10);
text1.setName("Text1");
add(text1);
JLabel label2 = new JLabel("Text2");
label2.setName("Label2");
add(label2);
JTextField text2 = new JTextField(10);
text2.setName("Text2");
add(text2);
// Register a key event post processor.
KeyboardFocusManager.getCurrentKeyboardFocusManager()
.addKeyEventPostProcessor(this);
}
public static void main(String[] args) {
JFrame f = new KeyListenerF1Demo();
f.setName("MyFrame");
f.pack();
f.setVisible(true);
}
#Override
public boolean postProcessKeyEvent(KeyEvent ke) {
// Check for function key F1 pressed.
if (ke.getID() == KeyEvent.KEY_PRESSED
&& ke.getKeyCode() == KeyEvent.VK_F1) {
// Get top level ancestor of focused element.
Component c = ke.getComponent();
while (null != c.getParent())
c = c.getParent();
// Output some help.
System.out.println("Help for " + c.getName() + "."
+ ke.getComponent().getName());
// Tell keyboard focus manager that event has been fully handled.
return true;
}
// Let keyboard focus manager handle the event further.
return false;
}
}
This should help
yourJFrame.setFocusable(true);
yourJFrame.addKeyListener(new java.awt.event.KeyAdapter() {
#Override
public void keyTyped(KeyEvent e) {
System.out.println("you typed a key");
}
#Override
public void keyPressed(KeyEvent e) {
System.out.println("you pressed a key");
}
#Override
public void keyReleased(KeyEvent e) {
System.out.println("you released a key");
}
});
Hmm.. what class is your constructor for? Probably some class extending JFrame? The window focus should be at the window, of course but I don't think that's the problem.
I expanded your code, tried to run it and it worked - the key presses resulted as print output. (run with Ubuntu through Eclipse):
public class MyFrame extends JFrame {
public MyFrame() {
System.out.println("test");
addKeyListener(new KeyListener() {
public void keyPressed(KeyEvent e) {
System.out.println("tester");
}
public void keyReleased(KeyEvent e) {
System.out.println("2test2");
}
public void keyTyped(KeyEvent e) {
System.out.println("3test3");
}
});
}
public static void main(String[] args) {
MyFrame f = new MyFrame();
f.pack();
f.setVisible(true);
}
}
I have been having the same problem. I followed Bruno's advice to you and found that adding a KeyListener just to the "first" button in the JFrame (ie, on the top left) did the trick. But I agree with you it is kind of an unsettling solution. So I fiddled around and discovered a neater way to fix it. Just add the line
myChildOfJFrame.requestFocusInWindow();
to your main method, after you've created your instance of your subclass of JFrame and set it visible.
lol .... all you have to do is make sure that
addKeyListener(this);
is placed correctly in your code.
You could have custom JComponents set their parent JFrame focusable.
Just add a constructor and pass in the JFrame. Then make a call to setFocusable() in paintComponent.
This way the JFrame will always receive KeyEvents regardless of whether other components are pressed.