JComboBox：ActionListener设置但getSelectedItem返回null

Question

我设置了一个jcombobox和actionlistener，填充了combbox，我选择了下拉名称，并且getSelectedItem保持返回null作为值：

  

ContactComboBox.addActionListener（new ActionListener（）{

        @Override
        public void actionPerformed(ActionEvent e) {

            ContactComboBox = (JComboBox) e.getSource();
            if ("comboBoxChanged".equals(e.getActionCommand())) {
                final Employee primary = (Employee) ContactComboBox.getSelectedItem();
                LOG.debug("Getting current contains for primary combobox {} ", primary);
                if (primary != null) {
                    primary.setPrimaryContact(true);
                    for (Employee emp : getEmployeeListCopy()) {
                        if (!emp.equals(primary)) {
                            primary.setPrimaryContact(false);
                        }
                    }
                }
            }
        }
    });