Focus problem in 1.4_2 after JPopupMenu show

Question

Hi, there:
I have an application, with a JTextField when that textfield gained focus, a popup menu is shown, and when it lost focus, the popup menu is hidden.
My focus listener class is listed below, where popup is JPopupMenu, and function displayPopup() is just to call show() in JPopupMenu:
     class MyFocusListener extends FocusAdapter {
          public void focusGained(FocusEvent e) {
               System.out.println("focus gained.............");
               displayPopup();
          public void focusLost(FocusEvent e) {
               System.out.println("focus lost ..............");
               popup.setVisible(false);
     }Everything works fine in jdk 1.3 version. In jdk1.4_2 version, I met following issues:
1. whenever the text field gained the focus, the application keeps calling "focusGained()", and "focusLost()" functions endlessly (it seems the system keeps sending those focus events endlessly);
2. if I removed that "popup.setVisible(false)" in focusLost, then, it seems no other component can gain the focus anylonger.
So, very appreciated if anyone can give me some help, is that a bug in 1.4.2 or is there any way to work around?
Thanks a lot
David

Answer 1

The reason is that in 1.4.2 each time you show a popup over a text field, it trades focus back and fourth with the text field a few times (2-3 times) before it is fully shown.
That means you gain focus... diaplay a popup -> which fires 2-3 more gain/lost focus -> and on each of those, you show a popup -> infinite loop.
Here is the overall tip: Don't try to show/hide popups based on foucs events. Make them controlled by something else, like clicking events.
If you must do this, you can use a timer to avoid the issue. Just make sure you are using showPopup(Component,x,y) in your displayPopup() method!
class MyFocusListener extends FocusAdapter {
  long lastTimeGainedFocus = -1L;
  public void focusGained(FocusEvent e) {
    long currentTime = System.getCurrentTimeMilliseconds();
    if(lastTimeGainedFocus == -1L || currentTime - lastTimeGainedFocus > 100) {
      displayPopup();
    lastTimeGainedFocus = currentTime;
  public void focusLost(FocusEvent e) {
     // do nothing here... popup should hide itself
}