Java Swing和JComboBox事件

Question

I have a JComboBox with multiple values in it. I need to be able to detect when the user clicks the JComboBox but does not change the currently selected item.

Neither itemStateChanged nor actionPerformed fire when this happens.

What event should I be using?

Answer 1

How about recording the combo box's state when the mouse button is pressed, and comparing it to the value the box has when the mouse button is released?

• attach a MouseListener to the JComboBox
• override the mousePressed() method to record the box's state to a temp variable
• override the mouseReleased() method to compare the box's value to the temp variable's value

At this point, it's a simple equality check.

Answer 2

Add a MouseListener to the JComboBox using its addMouseListener method. You will want to extend MouseAdapter and override only the mouseClicked method.

Answer 3

What if the user users the keyboard to open the popup and then uses the escape key to close the popup?

I would use a PopupMenuListener. This should handle both mouse and keyboard actions. The concept would be the same as other suggestions. When the popup is displayed you save the selected index. When is closes you compare the selected index to see it it has changed.

Answer 4

I was looking specifically at right mouse click on items, so it's a slightly different problem. But the solution for me was to

1. Subclass JComboBox substituting getCellRenderer( ) with a subclassed DefaultListCellRenderer .

2. In the cell renderer intercept getListCellRendererComponent() which has boolean isSelected , boolean cellHasFocus parameters and can be used to watch for mouse events and do list.setToolTipText() .

I'm sure the non-final selection change will get there, where it can be intercepted.