Unresponsive KeyListener for JFrame

Question

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

User · Answer

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);

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

lol      all you have to do is make sure that   addKeyListener this    is placed correctly in your code

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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                  amp  amp  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

User · Answer

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

User · Answer

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);

User · Answer

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

User · Answer

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

User · Answer

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                  amp  amp  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

User · Answer

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

User · Answer

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

User · Answer

lol      all you have to do is make sure that   addKeyListener this    is placed correctly in your code

[java] Unresponsive KeyListener for JFrame

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