I'm trying to listen for a window close event on the parent JFrame of a JPanel. In the WindowClosing event I'd like to de-register a listener to a different component.
Unfortunately the only code I can gaurantee to have run is the constructor for the panel. What this means is that the panel itself doesn't have an ancestor window yet, so simply calling SwingUtilities.getWindowAncestor doesn't work. So what I do is register a hierarchy listener, and in the hierarchyChanged event look for SHOWING_CHANGED event. When that even fires, now I can look for the window ancestor of the panel.
So basically I have the following:
class ShapeControlPanel extends JPanel{
public ShapeControlPanel(){
final ShapeControlPanel me = this;
me.addHierarchyListener(new HierarchyListener() {
#Override
public void hierarchyChanged(HierarchyEvent e) {
if((e.getChangeFlags() & HierarchyEvent.SHOWING_CHANGED) == HierarchyEvent.SHOWING_CHANGED){
SwingUtilities.getWindowAncestor(me).addWindowListener(new WindowListener() {
/* Snipped some empty handlers */
#Override
public void windowClosing(WindowEvent e) {
/* Finally get to remove the handler. */
me.getApparent().removeLocationSelectionListener(me.GUID(), me);
}
});
}
}
});
}
}
Is this sane? Is there a more reasonable way of getting a handle on the frame closing event?
It's not the ugliest thing I've seen (I wouldn't even say it's all that bad), but you have to ask yourself: why does your panel really need to know when the window is closed? It seems to be an odd coupling that would best be removed.
I don't know enough about your context and what you are truly trying to accomplish to suggest an alternative right now. But if a panel needs to know about the container in which it resides, there is probably some bad design with harmful coupling.
Related
I need to write a Java Swing application that will run and act about the same on Linux, Windows and Mac. And for virtually all Widgets I create, I need to add some special handling, including, everything needs to be able to pop up a menu when asked. Even widgets like labels and buttons.
I'm able to catch menu requests by adding:
MouseListener m = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e)
{
if (e.isPopupTrigger())
{
onMenuSummons(); //do my thing
}
}
};
addMouseListener(m);
to the constructor on my extended widget.
But I'm concerned that this is a Linux-only solution. Do I only need to check isPopupEvent() in MousePressed? What about MouseClicked? I could hook both to be sure, but do I run a risk that some platform someday would have isPopupEvent() be true in both functions for the same mouse action?
Ideally MouseAdapter would spare me the question by offering an overridable popupRequest(MouseEvent e), but it doesn't. So what is the always right, works everywhere on all platforms and always will forever solution?
Also, some of the widgets I'm extending may have their own popup menus; I need to suppress those and implement my own. How do I make sure only my own menu is displayed? TIA.
Read the section from the Swing tutorial on Bringing up a Popup Menu for the basic of using menus and popup menus.
To write a MouseListener the basic code is:
class PopupListener extends MouseAdapter {
public void mousePressed(MouseEvent e) {
maybeShowPopup(e);
}
public void mouseReleased(MouseEvent e) {
maybeShowPopup(e);
}
private void maybeShowPopup(MouseEvent e) {
if (e.isPopupTrigger()) {
popup.show(e.getComponent(),
e.getX(), e.getY());
}
}
}
some of the widgets I'm extending may have their own popup menus; I need to suppress those and implement my own.
Also note the the example from the tutorial is older. The newer approach for adding a popup menu to a component is to use:
component.setComponentPopupMenu(....);
Not sure, but since this method only allows a single popup it may replace the default popup?
Okay, so this might be a stupid question, but I'm new to Java and trying to teach myself things the right way before I develop any bad habits.
Anyway, I was writing a program last night that consisted of a custom class extending Frame and a custom class extending Canvas. The main() method is in the canvas class and I create an instance of the frame class there. The problem is that when the program detects a window close event, I can't dispose the frame because I seemingly have no way to access it from outside the main method. And if I try to define it outside of main(), then I can't use it within. So I ended up skipping dispose() and just using System.exit(0). Is this alright? Is it basically doing the same thing anyway? Or is this a problem I need to fix, and if so, any idea how?
Thanks so much for reading,
Cody
You can get a reference to the frame, from the source property of the event:
class MyWindowListener extends WindowAdapter {
public void windowClosing(WindowEvent e){
Frame frame = (Frame) e.getSource();
frame.dispose();
}
}
Alternatively, since this is an anonymous class (presumably) declared within the constructor, you also have access to the enclosing instance, so you can also write it as:
class MyFrameClass extends Frame {
public MyFrameClass() {
this.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
MyFrameClass.this.dispose();
}
});
}
}
Or you can make it simpler still (as your WindowListener does not have a method of its own called "dispose"):
public void windowClosing(WindowEvent e){
dispose();
}
Not a stupid question. Because of the garbage collector its not such a big issue, however, there are some times when you will want to execute some cleanup when a window closes. So some suggestions:
The Window Closing event should be handled from the Frame itself. For instance:
this.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
//code here to perform as the window is about to close.
}
});
And I would suggest that you create a separate class for your main method that will invoke the Frame etc.
This is used to close Jframe with an event handler.
current Jframe
public class LoginForm extends JFrame
{
LoginForm()
{
//Some code for Jframe and its components.
if(Condition)
disposewindow();
}
private void disposewindow()
{
WindowEvent closingEvent = new WindowEvent(LoginForm.this,
WindowEvent.WINDOW_CLOSING);
Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(closingEvent);
}
//you can can use for alternate of dispose()event and it post some event handler **Closing event** ,
// if we can use this closing event to open new window with conditions.
//It means closing child window with closing event, get this flag in main window to make main window as Disable or Enable state
}
//In parent window
#Override
public void windowClosing(WindowEvent arg0) {
// TODO Auto-generated method stub
this.frame.disable();
}
I've got a window and I would like to get notified when the position or the size has changed. Which type of listener is the best to take?
WindowListener didn't work for me.
You can use a ComponentListener which has the componentResized and componentMoved methods.
You might want to try
the HierarchyBoundsListener
myJFrame.getContentPane().addHierarchyBoundsListener(new HierarchyBoundsListener(){
public void ancestorMoved(HierarchyEvent e) {
doSomething();
}
public void ancestorResized(HierarchyEvent e) {
doSomethingElse();
}
see http://java.sun.com/docs/books/tutorial/uiswing/events/eventsandcomponents.html for a full list of listeners that all swing components support.
I have a component (JPanel) inside a Window.
I always get false when calling panel.isShowing(),
when calling from a windowGainedFocus() event (when the parent window gets focus).
I assume that when the windowGainedFocus() event is called, the painting of the JPanel within this Window had not been finished yet.
I was trying to place that call isShowing() on the paint() method of this Window,
but I always get isShowing() = false.
Is there a way I could get an event when the JPanel is fully shown on screen and the isShowing() method will return true ?
Thanks
You should probably best approach this with a hierarchy listener on the panel itself:
panel.addHierarchyListener(new HierarchyListener() {
public void hierarchyChanged(HierarchyEvent e) {
if ((HierarchyEvent.SHOWING_CHANGED & e.getChangeFlags()) !=0
&& panel.isShowing()) {
//do stuff
}
}
});
If you don't want an event but have some specific code that needs to be run after your component has been drawn, you can override addNotify(), which gets called to make the component displayable. Example:
public void addNotify()
{
super.addNotify();
// at this point component has been displayed
// do stuff
}
You component will be fully displayed after you receive WindowListener.windowActivated. You will also run into timing problems and race conditions trying to assign focus before the windowActivated event.
I'm currently trying to receive key events during a drag and drop, but it seems to me that the focus is taken away while dragging so that I can't listen to any key events.
I'm dragging a JComponent subclass that implements KeyListener and requests the focus in the DragSourceListener's dragEnter method, but my assumption is that the focus is taken away from it afterwards.
Now, who's got the focus and how can I take it away back to my JComponent. Or is there a different approach that is more suitable for dnd?
Thank you in advance.
UPDATE:
It's a lot of code necessary to make this work so I'm only going to post some snippets to show you what I'm trying to do:
public class Stone extends JComponent implements Serializable, KeyListener {
public Stone(...) {
//...
setFocusable(true);
addKeyListener(this);
this.dragSource = DragSource.getDefaultDragSource();
this.dgListener = new StoneDGListener();
this.dsListener = new StoneDSListener();
this.dragSource.createDefaultDragGestureRecognizer(
this,
DnDConstants.ACTION_MOVE,
this.dgListener
);
//...
}
//...
public void keyPressed(KeyEvent e) {
System.out.println("Stone: "+e.getKeyCode());
}
//...
public class StoneDSListener implements DragSourceListener, Serializable {
//...
#Override
public void dragEnter(DragSourceDragEvent dsde) {
//...
Stone.this.requestFocus();
addKeyListener(Stone.this);
}
//...
}
}
What happens is that before I'm dragging the Stone component my JPanel has the focus so it receives any keys I'm pressing.
During the drag I can't listen to any pressed keys(so I don't know who's got the focus) even though I'm requesting it when in dragEnter() and after I release the Stone any key events are send to the Stone.
It's probably not important for the question but to illustrate what I'm doing here's a screenshot:
image showing the "drag" http://img685.imageshack.us/img685/1884/pico.png
(Here I'm dragging the Stone from the collection below to the game field on the top). In this state I don't know how to find out what keys are pressed. I need to figure this out in order to be able to rotate the Stone.
Not sure who has focus during a drag and drop. But an alternative solution to your problem would be to add a KeyEventDispatcher for your Stone class to the KeyboardFocusManager. From the JavaDoc:
The KeyboardFocusManager is both a centralized location for client code to query for the focus owner and initiate focus changes, and an event dispatcher for all FocusEvents, WindowEvents related to focus, and KeyEvents+.
+ my emphasis.
Basically we use similar sort of code to intercept KeyEvents before they hit the Component that has focus.
Just gave it a quick test for your particular drag and drop context and it seems to work alright (as long as your application has focus within the operating system). Essentially something along the lines of:
Public Stone(...) {
// ...
KeyboardFocusManager fm = KeyboardFocusManager.getCurrentKeyboardFocusManager();
fm.addKeyEventDispatcher(
new KeyEventDispatcher() {
public boolean dispatchKeyEvent(KeyEvent e) {
System.out.println("Key Press: " + e.getKeyChar());
return false;
}
}
);
// ...
}
You will need to do a bit of leg-work on enabling and disabling when the user is no longer dragging and dropping as my test currently prints all the time.
I also wonder if it is possible to use the KeyboardFocusManager to determine who actually ends up with focus during a drag and drop?
Anyway, I hope this gives you a few new ideas to try.