There are a lot of topics on how to capture keystrokes in Java Swing, but I'd like to ask about the best practice. For example, I have a window in which I wish to listen to a keystroke of either F1 or Command-P on a Mac (or CTRL-P on a PC).
Reading The official Javadoc for KeyEvent, it seems that it is a better practice to use Key Typed events rather than Key Pressed or Key Released events, because they are higher-level. This makes sense to me, and I've even found that in order to make sure the program is platform-agnostic, I have to specify a keystroke object thusly:
private KeyStroke ks = KeyStroke.getKeyStroke(KeyEvent.VK_P, Toolkit.getDefaultToolkit().getMenuShortcutKeyMask());
This should allow for capturing of either the Command accelerator key on a Mac, and the CTRL accelerator key on a PC. (I hope I'm using those terms correctly.) So now that I have a KeyStroke object, how do I go about checking it against a KeyEvent object in my KeyListener? And throwing a check for an F1 key event as well only complicates the matter further, though hopefully not too much.
Suggestions?
So now that I have a KeyStroke object, how do I go about checking it against a KeyEvent object in my KeyListener?
You don't use a KeyListener. Swing was designed to be used with Key Bindings.
Check out Key Bindings which contains a program to list the default bindings of each Swing component. It also give some example of how you might create your own ey Bindings. It also contains a link to the Swing tutorial on Key Bindings which explains the whole process in more detail
I am making a simple game(my first time using key reader) and am using WASD inputs to move the character. I want to make it so that if you press, say, W and A at the same time, you go diagonal. Does anyone know how to do this?
Don't use a KeyListener. Swing was designed to be used with Key Bindings.
Either way you can't listen for multiple keys at once so you need to keep track of which keys have been pressed. Since you want to do animation you would generally use a Swing Timer to schedule the animation. Then every time the Timer fires you check which keys are pressed and move you character based on the keys pressed.
Check out KeyboardAnimation.java source code from Motion Using The Keyboard for an example that demonstrates this approach. This article also gives reasons why key bindings are preferred over a KeyListener.
I am trying to write a program that uses key events to activate a method. The code works on Windows machines but when transered to Mac it does no respond to my "Spacebar" being pressed. I presume this is to do with the different key codes used.
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_SPACE) {
System.out.println("SPACEBAR");
grid.stepGame();
}
}
Any ideas how i can get this working on Mac?
Edit - The problem has been solved using the answer below - For note though it seems that on Mac the Frame never automatically regains focus, hence why the keylistener doesn't work is another JComponent is activated.
I'm uncertain as to your particular issue but it's a good bet that if you switch to using key bindings instead of key listeners your issue would disapear.
From the Java Tutorials site:
Note:
To define special reactions to particular keys, use key bindings instead of a key listener.
As an example
// Component that you want listening to your key
JComponent component = ...;
component.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0),
"actionMapKey");
component.getActionMap().put("actionMapKey",
someAction);
When I press "Delete" button on the keyboard, program gets three events - KEY_PRESSED, KEY_TYPED, and KEY_RELEASED. The problem is, in KEY_PRESSED and KEY_RELEASED, parameter "keyCode" is set, but in the KEY_TYPED it is not (in fact, there no meaningful info in that event). With F5 key, it is even funnier - KEY_PRESSED and KEY_RELEASED are registered, but KEY_TYPED never occurs.
The listener was added via Toolkit.getDefaultToolkit().addAWTEventListener(). Using JDK 6.26.
What could be my problem?
EDIT:
Here are the events that happen when Delete key is pressed:
java.awt.event.KeyEvent[KEY_PRESSED,keyCode=127,keyText=Delete,keyChar=Delete,keyLocation=KEY_LOCATION_STANDARD,rawCode=119,primaryLevelUnicode=127,scancode=0] on javax.swing.JButton[,0,0,61x30,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.synth.SynthBorder#50f38cf0,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=javax.swing.ImageIcon#6ae2d0b2,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=0,bottom=0,right=0],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=SVG,defaultCapable=false]
java.awt.event.KeyEvent[KEY_TYPED,keyCode=0,keyText=Unknown keyCode: 0x0,keyChar=Delete,keyLocation=KEY_LOCATION_UNKNOWN,rawCode=0,primaryLevelUnicode=127,scancode=0] on javax.swing.JButton[,0,0,61x30,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.synth.SynthBorder#50f38cf0,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=javax.swing.ImageIcon#6ae2d0b2,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=0,bottom=0,right=0],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=SVG,defaultCapable=false]
java.awt.event.KeyEvent[KEY_RELEASED,keyCode=127,keyText=Delete,keyChar=Delete,keyLocation=KEY_LOCATION_STANDARD,rawCode=119,primaryLevelUnicode=127,scancode=0] on javax.swing.JButton[,0,0,61x30,alignmentX=0.0,alignmentY=0.5,border=javax.swing.plaf.synth.SynthBorder#50f38cf0,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=javax.swing.ImageIcon#6ae2d0b2,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=0,bottom=0,right=0],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=true,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=SVG,defaultCapable=false]
better would be implements KeyBindings
part of keyboard are reserved Keys for built-in JComponent funcionality, more informations from #camickrs UIManager Defaults
depends of reason(s) why you needed implents KeyListener, because for there are lots of another Listeners for various JComponent, that should be filtering or register text changes inside
some of JComponent Models generated Events from Mouse and Keyboard input
From the JavaDoc The "key typed" event. This event is generated when a character is entered. In the simplest case, it is produced by a single key press. Often, however, characters are produced by series of key presses, and the mapping from key pressed events to key typed events may be many-to-one or many-to-many.
You are trying to get the F5 key which is probably not registered as a character being entered. By using the KEY_RELEASED you will consistently get the result you are looking for and the API is behaving as expected.
Key typed events ALWAYS generate '0' as the key code. Look up the method getKeyChar() instead, or (as has been suggested) listen for keyReleased() instead.
getKeyChar(): http://goo.gl/ajH03
A shout out to the Swing gurus out there!!
I've been doing Swing programming for several years but have always been unclear on this.
As you know Swing/AWT gives you several ways to execute a particular action when a button is clicked. I've seen it done several different ways in the applications I've worked on. The project I'm currently working on tends to follow this approach:
someButton.setActionCommand("mycommand");
someButton.addActionListener(listener);
--snip--
public void actionPerformed(ActionEvent event) {
String command = event.getActionCommand();
if (command.equals("mycommand"))
doThis();
else if (command.equals("someothercommand"))
doThat();
etc.
This seems kind of clunky to me - is there any benefit to this style of programming, or is it better to use Swing Actions?
Or are there different situations where the different approaches are better/worse?
IMO, it is better to use separate listeners for Actions.
That way you leave the delegating of what action should happen up to Swing. You don't have to compare Strings to decide what to do.
Having one huge ActionListener for more than one action feels like breaking the pattern to me.
From a design point of view, I think it is better to have one class to handle one specific action for a component as opposed to one class that is a "lets handle everything for all components here" type of design.
Also, if you use Action you can a) apply it to more than one component (e.g. a button and a menu item) b) call setEnable to enable/disable it for all components its attached to and c) Also use it to define various settings on the components its attached to (namely, the text label, the tooltip text, the accelerator key, icon, etc.). This last one is done via the putValue method and calling this method again will change the settings for all components its attached to.
Specifically, I would advise to subclass AbstractAction for your needs.
I know that's demo code but since you're working on this stuff I thought I'd mention that swing tends to be really repetitive if you're not careful.
Using Action classes tends to let you refactor better. In swing, one of the best ways to start is to ensure that NO strings are in your code. Nearly every "New" will be in a loop of some sort, reading from a dataset (Often the dataset is as simple as an array)--Once you start reading from a dataset like that, actions can help you a lot.
You use data to create your action, data to create your control, and data to associate the two--in this way you can end up very close to (or at) 0 lines of code for a new control.
Once you start programming this way and can see the patterns, it's at least as quick as the repetitive way and much less error prone.
its Useful if you have several buttons or components that perform the same action (ie. several exit buttons on the same page will use the same code)
Set them all to the same action command and they will all use the same code in the listener
JButton.addActionListener(this);
JButton2.addActionListener(this);
JButton.setActionCommand("exit");
JButton2.setActionCommand("exit");
public void ActionPerformed(ActionEvent e){
if(e.getActionCommand=="exit")
System.exit(0);
}